Fume Hood White Papers

Fume Hood Sash Glass: What Do Standards and Specifications Require?

Robert Haugen, Ph.D., Flow Sciences


The most obvious barrier between a lab worker and a potential experimental accident is the fume hood sash. Ideally, we want such a sash to protect the researcher from eruptions, spatters, and other dangers present in typical reactive chemistry.

Like many other issues involving materials of construction, fume hood glazing comes in a variety of designs and specifications.

The writer will set forth the glass types available for fume hood construction and discuss standards typically used to help specify this glass in a useful manner. It will also be noted that some safety glass types now specified are neither preferred nor reliably defined.

These issues of vagueness lead to confusion among lab planners and specifiers attempting to describe fume hood glass that is appropriate for a given application.

Sash Glass Options Often Specified for Chemical Fume Hoods:

  • Annealed glass: While annealed glass is never used in fume hoods 23, its manufacturing process gives us a clue about various strengthening procedures we will later describe in detail.

Annealed glass is glass produced without internal stresses imparted by heat treatment, i.e., rapid cooling, or by toughening or heat strengthening. Glass becomes annealed if it is heated above a transition point then allowed to cool slowly, without being quenched. Glass is treated with heat in order to change its properties by the annealing process. Annealed glass is the most common glass used in windows. Annealed glass is also known as a standard sheet of float glass.”22

“Glass which has not been annealed is liable to crack or shatter when subjected to a relatively small temperature change or mechanical shock. Annealing glass is critical to its durability. If glass is not annealed, it will retain many of the thermal stresses caused by quenching and significantly decrease the overall strength of the glass.”22

So annealed glass, because of its method of manufacturing, is free of irregular internal stresses which can make glass fragile and more brittle. The product we start with in any strengthening procedure is therefore stress-free and capable “as is” of reliable use for many construction purposes.

1) Laminated Glass:

This form of safety glass is designed to hold together when shattered2. Laminated glass is typically constructed from annealed glass lites with a layer of some kind of plastic in the middle (interlayer). The interlayer is typically PVB (Polyvinyl butyral) or EVA (ethylene-vinyl acetate). Both interlayer types form a bonded interface with the glass, making a sandwich that is very difficult to penetrate or shatter. Either interlayer material type tends to hold the glass together when the panel becomes damaged through impact.

Most specifications sent to Flow Sciences for quotation call out a PVB interlayer and a total glass –interlayer-glass thickness of not less than 7/32”. Flow Sciences uses nominal ¼” glass as our standard.

2) Tempered Glass:

If we start with stress-free annealed glass, we can re-heat this glass and rapidly cool it in a manner that puts a regular and uniform stress pattern into the glass structure. “Glass of any shape that has been subjected to a thermal treatment process characterized by uniform heating followed by rapid uniform cooling to produce compressively stressed surface layers is called tempered glass.” See ASTM C1048 for additional information.7

As a result of its safety and strength, tempered glass is used in a variety of demanding applications, including passenger vehicle windows, shower doors, architectural glass doors and tables, refrigerator trays, mobile screen protectors, as a component of bulletproof glass, diving masks, and various types of plates and cookware. 4

In chemical fume hood applications, extreme heat would require tempered glass which does not fracture due to heat until about 450o F. Laminated safety glass may crack at or above 160o F. When tempered glass does break, the entire sheet winds up in tiny glass shards due to the uniform stressed structure that increases its resistance to impact.

At least one major fume hood manufacturer6 is currently using ¼” tempered glass fume hood sashes. Flow Sciences and most other North American manufacturers use laminated safety glass.

3) Laminated-tempered Glass:

“Laminated/Tempered glass is a hybrid of two strong types of glass: Laminated glass, which consists of two glass panes with a thin, clear vinyl layer in between that prevents the glass from shattering on impact, and tempered glass, which has been heat-treated to make it harder and more durable than standard glass.9

This type of glass appears occasionally in fume hood specifications. It creates several problems for companies seeking to provide fume hoods with this glass:

  1. Fume hood design requires glass parts of non-standard dimensions (sash, bypass panels, light lens, etc.). All glass lites to be used to make a piece of lami-temp must be first pre-cut into two sets of pieces from non-tempered glass. These lites are then tempered in an oven to create thin (~2 mm) tempered glass panels. Each matching pair of panels must then be laminated together using a PVB interlayer. Typically, this safety glass must have a total thickness of no more than ¼”. Unfortunately, one cannot start with a big sheet of lami-temp glass and cut it, because the cutting motion will cause the piece to shatter at the instant the surface is scratched. Therefore, one must start with pre-cut lites of annealed glass, temper them, and then laminate matching tempered pieces together.
  2. The method described above of manufacturing each piece of laminated-tempered glass is time and labor consuming. Lites this thin are difficult to temper and then laminate due to breakage and other issues. There is no alternate way to make custom cut pieces with any better efficiency. Most fume hood manufacturers find the cost and manufacturing risk of this product prohibitive for standard product, and only offer this option if specified by the customer.

4) Other types of glass occasionally used in fume hoods.

Infrequently, other types of fume hood sash glass have been specified:

  1. “Bullet proof” glass is usually a combination of polycarbonate (Lexan) and glass in layers. The illustration below shows a cross section of this product comprised of two glass layers and three layers of polycarbonate film.11

    This material is usually sold in thicknesses greater than ¼” The department of defense has specified this product be used in some marine fume hood applications. Again, the constituent glass parts must be made separately and then joined together for each piece as the product cannot be cut once fabricated.

  2. Fire-Rated Wired Glass is infrequently specified for laboratory hoods. Years ago, the researcher saw a fume hood similar to ones shown below at the University of Illinois with wired glass throughout. There can be serious problems with this product.

The presence of the wire mesh appears to be a strengthening component, as it is metallic, and conjures up the idea of rebar in reinforced concrete or other such examples. Despite this visual implication, wired glass is actually weaker than unwired glass due to the incursions of the wire into the structure of the glass. Wired glass often may cause heightened injury in comparison to unwired glass, as the wire amplifies the irregularity of any fractures. This has led to a decline in its use institutionally, particularly in schools.12

The Influence of Various Standards on Fume Hood Glazing:

1) ANSI / AIHA Z 9.513 is the over-arching standard for fume hoods and other lab containment equipment. It calls out other standards within its arc of proper lab outfitting including fume hood containment testing and materials, including glass. ANSI AIHA Z9.5 states that fume hood sash glass should be shatterproof (no standard referenced).

No other codification, identification or mention of sash glass material or other glazing practices in fume hoods is mentioned in this entire standard. Not much help here!

2) SEFA 1 14 is a different standard written by members of the Scientific Equipment and Furniture Association.

Section 4.1.8, 2016 States: “Most lights are fluorescent tubes housed outside the hood chamber and separated by a vapor resistant safety glass panel in the top of the hood. The standard does not specify what type of safety glass should be used and what standard should be applied. Not much help here either!”

3) ANSI Z97.1 – 2015 15 delineates the most comprehensive list of definitions and standards for various forms of safety glazing:

a) Laminated

b) Tempered

c) Organic coated

d) Plastic

It must be emphasized, however, that no definition of laminated-tempered glass is offered herein.18

ANSI AIHA Z97.1 offers separate methods for testing laminated and tempered glass, but says nothing about testing or certifying laminated-tempered glass, even though there are major differences in the cracking, initiating energy, and thermal behavior of these materials.

This section is reproduced below to show how the standard does not specifically address laminated-tempered safety glass:

Note: Even though the above text of Z97.1 reviews SEPARATE methods for “shot bag” testing laminated and tempered safety glass, by industry convention, any laminated glass made up of any kind of glass lites is regarded as laminated glass and is tested using column two criteria of the ANSI Z97.1 – 2015 standard. Flow Sciences obtained samples of lami-temp glass 8mm thick for testing and evaluation. Each sheet came with the permanent label shown in the photo below:

There is inherent confusion in this label. Note the “HS” in the expression TEMPERED/H.S. It turns out that tempered glass comes in several categories, including HS (heat-strengthened) and FT (fully tempered). Here is a definition from the literature of HS and FT grades:

“The most dramatic and important difference between heat strengthened and tempered glass is in the post breakage characteristics of the two products (i.e. break pattern). If heat strengthened glass (HS) should break, the pieces will be relatively large and tend to remain in the glazing system until removed. Tempered glass, on the other hand, is designed to break into innumerable small, roughly cubical pieces. In fact, it is this break pattern that qualifies tempered glass as a safety glazing material. However, because of the break pattern, tempered glass is much more likely to evacuate the glazing system immediately upon breakage. Responsible design professionals must consider the tendency of tempered glass to evacuate the opening upon breakage and the consequences must be acceptable. Responsible parties know that there is always a possibility of glass breakage. The glass construction must be designed with a low probability of breakage, typically less than 8 panels per 1000 panels, but if the glass does break, the glass design must be done in a manner so that the breakage consequences are acceptable.” 20

A more direct explanation is offered by Vitro Architectural glass22:

“There are two different types of heat-treated glasses, heat-strengthened and tempered. The similarities between the two include:

  • Production using the same processing equipment
  • Heating the glass to approximately 1,200 degrees Fahrenheit, then force-cooling it to create surface and edge compression

The differences between the two glasses are as follows:

  • With tempered glass, the cooling process is accelerated to create higher surface compression (the dimension of force or energy per unit area) and/or edge compression in the glass. It is the air-quench temperature, volume and other variables that create a surface compression of at least 10,000 pounds per square inch (psi). This is the process that makes the glass four to five times stronger and safer than annealed or untreated glass. As a result, tempered glass is less likely to experience a thermal break.
  • With heat-strengthened glass, the cooling process is slower, which means the compression strength is lower. In the end, heat-strengthened glass is approximately twice as strong as annealed, or untreated, glass.”

Heat-strengthened (HS) laminated-tempered glass shatters into relatively large pieces when cracked, held together by the plastic interlayer.

This breakage pattern is actually better in some applications than an FT laminated panel, which would totally fracture into tiny cubes held together by the interlayer. Such broken panels of FT lami-temp could drop or sail into a work area like a “wet blanket.” See photo below:

4) ASTM C1048-18 also describes various types of tempered and laminated glass.

The C1048-18 abstract states the following:

“This specification covers heat-treated flat glass – kind HS, kind FT coated and uncoated glass used in general building construction. Glass furnished under this specification shall be of the following conditions: condition A – uncoated surfaces, condition B – spandrel glass, one surface ceramic coated, and condition C – other coated glass. Flat glass furnished under this specification shall be of the following kinds: kind HS – heat-strengthened glass shall be flat glass, either transparent or patterned, in accordance with the applicable requirements, and kind FT – fully tempered glass shall be flat glass, either transparent or patterned in accordance with the applicable requirements. All fabrication, such as cutting to overall dimensions, edgework, drilled holes, notching, grinding, sandblasting, and etching, shall be performed before strengthening or tempering and shall be as specified….”

Note the last sentence above: once glass is tempered, it may not be cut. This material cannot be dimensionally field modified. Incidentally, nowhere in this standard is laminated-tempered glass mentioned.

5) 16 CFR 1201: This is part of the larger standard Code of Federal Regulations Title 16: Commercial Practices. Part 1201 is the Safety Standard for Architectural Glazing Materials. It contains the principal set of rules and regulations issued by federal agencies regarding commercial practices for glass.

Discussion: Where Are We left?

On the positive side, American manufacturers are given clear ways to label and classify laminated, tempered, or laminated-tempered safety glass. The operative standard here would be ANSI Z97.1. Additional information on classifying tempered safety glass is provided in ASTM C1048.

Below is the label marked on every sheet of standard laminated safety glass Flow Sciences receives, cuts, and then uses in the Saf T Flow fume hoods manufactured here in the United States. Among other standards, note ANSI Z97.1 is prominently referenced. Tempered, laminated, and lami temp glass are certifiable under the same standard using different pass-fail criteria.

On the negative side, customers occasionally want a different glass product than laminated or tempered. As contradictory as it sounds, the common practice is to test lami temp using the laminated test criterion, not the tempered criterion.

The tests and descriptions for lami-temp glass neglect to specify whether the “tempered” glass used is FT or HS. Several construction specifications call out laminated-tempered glass and say nothing about this issue. The following two examples demonstrate how these vaguely defined and poorly established distinctions can cause serious problems with fume hood glass specifications:

1) A major University requested laminated-tempered glass. It requires 91% transmission or better, Category II compliance under 16 CFR 1201, and a permanent marking from SGCC delineating compliance with listed standard. The specification says nothing about the degree the lites must be tempered.

There is another problem with the same specification: The specified requirement for testing using 16 CFR 1201 Category II criteria states Category II glass must be used in one of the following building components: shower doors, bathtub doors, sliding glass doors (patio type), storm doors or combination doors that contain any piece of glazing material greater than 9 square feet in surface area, doors that contain any piece of glazing material greater than 9 square feet.” CFR 1201 is therefore not applicable using this specification because none of the included Category II materials are fume hood sashes.

As stated earlier, the CFR 1201 Category II dimensional requirements come from the construction industry, where larger thin pieces of FT laminated-tempered glass, when stressed, turn into a one-piece “wet blanket” and may fall out of their frame on a building exterior and become a massive and dangerous falling object.17 The writer therefore believes the large-piece dimensional size requirements are designed to encourage thicker glass panels that will not fall out of their frames when they become shattered. Even though fume hoods are not one of the limited list of products specified in this standard, it is easy to see why CFR 1201 limits the use of laminated-tempered safety glass even in building and construction applications.

Flow Sciences has not wished to use lami-temp glass ¼” thick for fume hood sashes because either (or both) glass lites comprising a panel could easily crack and precipitate a collapse of the entire panel into a single mass of shards which will then potentially fall out of the sash frame in one piece.

2) A second specification for fume hood sash glass was found to call out lami-temp that would comply with ANSIZ97.1, grade B impact performance.

Grade B impact performance is clearly defined in the standard and easy to evaluate whether the two panels used in the structure are glass or tempered glass. As with most fume hood manufacturers, Flow Sciences has its laminated ¼” sash glass fully certified using ANSI Z97.1 to this procedure and will gain no improved impact performance going to lami-temp panels.

In summary, Flow Sciences has found limited advantage in the lami-temp product for many of the reasons cited above. If laminated-tempered glass must be used it should be grade HS since damaged panels have larger pieces less likely to fall out of the framing system. The remaining issue is fully tempered and heat strengthened are poorly differentiated in the standards.

FSI has found laminated glass serves most lab needs better than tempered or lami-tempered products. Laminated glass also has a well-established and regularly-applied standard which makes it useful for upholding our ISO 9001:15 consistency and standard compliance. Under present guidance from relevant standards, HS Lami-temp may not!



1) The researcher found three types of glass most commonly used in fume hoods: Laminated, tempered, and laminated-tempered.

2) Two types of glass, bullet proof and wired glass, are of minor importance in today’s fume hood market.

3) Fume hoods customarily use laminated or tempered safety glass. Both are typically furnished in either 7/32” or ¼” thicknesses depending on the manufacturer. Both may be tested for compliance using separate criteria in ANSI Z97.1.

4) In distant third place, is the sometimes-specified laminated-tempered safety glass. While such glass has improved performance at high temperature and better impact resistance than laminated glass, it is very complicated to quickly supply or replace and impossible to certify using a standard relevant to fume hood applications. There is an understandably larger cost for the lami-temp manufacturing process which involves factory cutting and piecing together the tempered pieces into the final laminated product.

5) One final point needs to be made regarding fume hood glass standards. The origin of a standard is important when deciding how to apply it to a component of a manufactured product. Department of transportation standards should test products that transport things. The construction industry should use standards related to building products. The fume hood industry, through appropriate groups, should promote or develop glass standards relevant to glass component safety in fume hoods.

As a fume hood manufacturer, FSI must seriously consider glass standards specifically related to fume hoods and their unique safety challenges. This final consummate issue will be developed in a future white paper!

1. “Fume Hood Incident”, MIT 7/2017, https://ehs.mit.edu/site/fume-hood-incident-july-2017

MIT Environment, Health & Safety Office; 265Massachusetts Ave, N52-496Cambridge, MA 02139

2. “Laminated Glass”; https://en.wikipedia.org/wiki/Laminated_glass; 1/21/2019

3. Maryland Glass Doors and Window Repair; http://mdglassdoorsandwindowrepair.com/laminated-glass

4. “Tempered Glass”; https://en.wikipedia.org/wiki/Tempered_glass; 12/5/2018; italicized portion in the text is a direct quotation from this citation.

5. 55 Glass Supply; https://www.55glass.com/temperedglasslosangeles.php;

6. CampbellRhea Lab Shield Fume Hoods; https://www.iciscientific.com/category/labshield;

7. ANSI Z97.1-2015; American National Standard for Safety Glazing Materials Used in Buildings -Safety Performance Specifications and Methods of Test

8. http://www.build.com.au/laminated-glass

9. https://www.onedayglass.com,

10. https://www.youtube.com/watch?v=KvFoNG7pXdk

11. http://security.tssbulletproof.com/bullet-resistant-glass-vs-window-security-film

12. https://en.wikipedia.org/wiki/Safety_glass


14. SEFA 1- 2017, p57 section 4.8.1

15. ANSI Z97.1 – 2015, Sections 4 and 5

16. Partial direct quotation from ABSTRACT of ASTM C1048-18

17. https://www.glassonweb.com/article/post-breakage-strength-testing-overhead-laminated-glass-applications

18. ANSI Z97.1-2015, Section C

19. https://ehs.berkeley.edu/lesson-learned-dry-scraping-causes-chemical-explosion

20. http://ravensbyglass.co.uk/wp-content/uploads/2015/04/Ravensby-Glass-Technical-Document.pdf, Ravensby Glass, UK

21. http://glassed.vitroglazings.com/topics/heat-strengthened-vs-tempered-glass

22. http://www.glazette.com/Glass-Knowledge-Bank-79/Annealed-Glass.html

23. Kewaunee, Jamestown, Hamilton, Mott, Flow Science, Labconco specifications all refer to either Laminated or Tempered safety glass for fume hood sashes.

Director of Product and Technology Development

Robert K Haugen  currently designs chemical laboratory containment equipment and develops new relevant technologies for Flow Sciences Inc.in Leland, North Carolina. He has also held positions at Kewaunee Scientific, Jamestown Metal Products, and St. Charles Manufacturing in similar capacities for 31 years. Previously, he did analytical chemical work at the University of Illinois (DNA, wastewater, and crop research) and Lawrence Livermore Labs in California (nuclear weapons research).

Dr. Haugen began his career as a curriculum writer for the Illinois Office of Education, developing texts on energy, urban management, and industrial pollution topics.

He received all his degrees from the University of Illinois in Urbana-Champaign, and is currently a member of the American Society of Heating, Refrigeration, and Air Conditioning Engineers, the American Chemical Society, and the National Fire Protection Association. He has participated in the development of both ASHRAE 110-1995 and the current 2016 update.

Chemical Fume Hoods : Four Truths about Price

Dr. Robert K. Haugen
Flow Sciences, Inc.



Flow Sciences manufactures containment equipment for the pharmaceutical, chemistry, and education communities. Like many manufacturers serving these customers, we try to build products that work. Particularly with safety equipment, we believe providing protection from fumes and toxic powders is a mission worthy and beneficial to mankind.

We do not believe the question of price to be unimportant, sacrilegious, or presumptive. It is however complicated, misunderstood, and in some cases misapplied, particularly regarding lab containment and safety equipment.

We propose here to review four truths about lab safety equipment pricing. At the end of this examination, the author will demonstrate how to view pricing in a comprehensive and useful manner.



Truth one : Before we evaluate a price, we must know how complete the price is.

Flow sciences makes six major categories of containment devices. While each category has unique characteristics, they all share elements and capabilities that influence their price.

Because chemical fume hoods are a staple both in labs and generally in the construction industry, we will focus on fume hood prices as reflective of how price has become a confusing issue in the entire containment industry.

Many times, a “standard fume hood price” does not even include the cost of a work surface. In a specify/provide marketplace, when something is not called out, it is not provided. Buyer beware! In the same market, base cabinets upon which the fume hood rests are only quoted if specified. Most companies making this product charge for shipping from the factory to the jobsite, but make this a separate line item.

All electrical equipment (lights, velocity alarms, fans, fan switches, etc.) are also typically extra. Finally, the equipment shipped must be de-trucked and distributed to rooms, then installed. Many times such expenses are hidden somewhere in a quotation, or ignored.

Before we look a price, at least all these elements highlighted above must be identified and included.

Truth two : Before we evaluate price, we must know if “extra” features we may depend upon are included.

Newer, more advanced aerodynamic fume hoods inherently contain fumes at lower face velocities and will require much lower volumetric throughput to operate. Do you care? Paying about 20% more for an energy efficient hood may cut annual energy costs in half1. Over a 15-year hood life span, this may save $50,000 in energy costs, or three times the original hood cost!

I’d care!

Some hoods are designed to be repaired and maintained easily, others are not. Some hoods have built-in framing and hardware allowing easy addition of monkey bars, most do not. Some hoods have a standard interior working depth over 24”, many do not. Some hoods have interior access panels that cannot dislodge during a fire or explosion, many do not.

The Flow Sciences fume hood has a standard slide-out work top for easy maintenance and standard pre-plumbed flexible service lines for easy repair and service outlet modification during hood life. Are these features important to you?

Truth 3 : Unless a hood contains fumes effectively, it is less than worthless! Institutional liability, personnel injury, and documentable expectations are all reasons why lab accidents and exposure to chemicals are to be avoided at all costs!

Does your recently purchased fume hood come with a test report showing it has been verified through testing to keep even small concentrations of a tracer gas from invading the worker’s breathing zone? Most reputable manufacturers can readily furnish such data for standard product2. Some manufacturers like Flow Sciences furnish reports for custom products too3.

Providing such a report on custom units costs money. Is it worth more money to memorialize the performance of a new containment device? Avoid an injury? Prevent procedural re-dos and litigation at your facility?

Many times in the heat of a legal battle over injury liability, institutions have blamed managers, instructors, and even victims for inviting accident exposure4. What is not realized is most lab safety equipment companies have written and produced safety manuals and videos  explaining proper research technique with their equipment. Flow Sciences has such materials. We have also published many papers on our website detailing tests we do3 and how this research demonstrates containment of our equipment during programmed use 4. Is this data something your company would value?

Truth 4 : If the reader already understands truths 1-3, the question at this juncture is, how can I get an equipment price that includes all the relevant factors discussed above which are important to my research?

The answer to this question may require you develop a written product specification that takes all the guesswork out of quoting your containment device properly. The writer is not talking here about a manufacturer’s proprietary specification, but a spec that truly reflects customer requirements and the complexities discussed so far in this paper. 4

Each subcontractor needs to know where their responsibility begins and ends. Performance of the product should be primary. Metal gauges and number of hinge knuckles secondary.

Many manufacturers have written specifications for their containment products. Flow Sciences publishes theirs in CSI Standard Format, Microsoft Word. We recommend using the FSI specification as a template, and modifying it to call out exactly what is needed in the product you intend to purchase.


These are the four truths. Satisfy them and your price will be meaningful and accurate:

  • Inclusiveness : All relevant price elements specified and included
  • Features : Specify and include features important to you
  • Safety : Specify and include materials on equipment operation, proper installation, and safe use
  • Memorialization : Provide documentation of performance under specified conditions.

So, how much does it cost? Apply the four truths reviewed above. They might just set you free!


  1. https://www.flowsciences.com/fume-hood-energy-savings-low-hanging-fruit/, Fig1,
  2. Summary, Containment Testing of Saf T Flow Chemical Fume Hoods, 4/1/19, Flow Sciences Inc., Dr. Bob Haugen
  3. Phase – Off. An Evaluation of a Flow Sciences, Inc. Fume Hood in The Containment of Solids, Liquids and Gases, Allan Goodman and Robert Haugen, Flow Sciences, April 2019 Gase
  4. https://dailybruin.com/2014/10/17/uc-spends-almost-4-5m-in-laboratory-fire-case/
  5. https://www.flowsciences.com/vav-equipment-specified-laboratory-hoods/

For More Information – Contact Us

Evaluating a Chemical Fume Hood for Containment of Solids, Liquids, and Vapors Using ASHRAE 110, HAM, and ISPE Methods

Allan Goodman, Ph.D., Flow Sciences
Robert Haugen, Ph.D., Flow Sciences


Flow Sciences has more than three decades of experience in designing, manufacturing and testing powder containment devices, predominantly for the pharmaceutical industry. These enclosures have evolved from small balance containment devices connected to remote blowers, to a variety of custom and standard products.

This increased product diversity has been achieved while maintaining the necessary features required for superior containment and airflow conditions conducive for enabling highly sensitive operations such as microbalance weighing and mixing and reacting chemicals.

No product reflects this sophistication more elegantly than the chemical fume hood. Originally designed around 350 years ago to contain accidents and prevent bad odors in the laboratory, the fume hood has become a device that can routinely produce control levels of vapors down to the part-per-billion level. This is particularly important because many researchers may be unaware of the toxicity or even the identity of chemicals routinely produced in experimental chemical reactions.1

In the United States, the primary containment measurement methodology for fume hoods since the late 1970’s has been ASHRAE 110. The latest version of this test, ANSI / ASHRAE 110-2016, uses an SF6(g) diffuser and mannequin with air sampler to determine a tracer gas presence in the breathing zone of a mannequin.2 A limitation of the ASHRAE test is that it is mostly static in nature and, other than the Sash Movement Effect (SME) component, involves no human interaction. In spite of these limitations, most manufacturers of fume hoods sincerely believe that containment of SFgas under the ASHRAE test conditions is a reasonable predictor for particulates as well as vapor containment.

This argument remains unconvincing for many of our customers. Indeed, many industrial hygiene organizations and personnel have not recommended the use of fume hoods for powder manipulation operations of any kind. It is therefore necessary to find new tests which quantify performance and limitations for fume hoods in the context of finely divided powders.

We have therefore chosen here to meld existing techniques centered around ASHRAE 110 with widely-accepted particulate containment measurement techniques4. This combined regimen was then directly applied to a 4’ fume hood so results of all tests could be compared with each other.  If results were found to be consistent, a new combined test using all three phases of matter could be established.

The test results obtained here allow us to make some rather positive preliminary conclusions in this regard.


Flow Sciences offers a wide range of enclosure types, including the ‘Saf – T Flow’ series of fume hoods.  The FAF483055VAA fume hood has a vertical sliding sash enclosure, and airflow through the unit is achieved using a duct system to an exhaust fan with air leaving the building. (Figure 1)

Testing of the unit was broken out into the following components:

  • ASHRAE-110
    • Face Velocity
    • Smoke Visualization
    • Tracer Gas
  • HAM
  • Surrogate Powder / Solvent

The ASHRAE-110, SF6HAM and surrogate material tests were performed at the Flow Sciences facility in Leland, NC.

Other than the SME, the ASHRAE-110 test is static in nature, while the other components are dynamic and require human interaction in and around the face opening of the fume hood. The various tests use different materials, allowing the tests to be used independently, to validate containment performance of the fume hood, or compared to one another to determine each test method as a predictor of the level of containment offered by the equipment.



Materials used for the testing of the fume hood are either used in standard testing or are acceptable surrogates.  Sulfur hexafluoride is the tracer gas used for the ASHRAE testing and is released at a constant rate determined by the ASHRAE-110 standard.  Lactose is an acceptable surrogate powder as defined by the ISPE good practice guide – Assessing the Particulate Containment Performance of Pharmaceutical Equipment.  Methylene chloride was chosen as the solvent as it is fairly volatile at ambient temperature and does not have appreciable solubility capacity for lactose.  For both of the surrogate materials, sufficient quantities were utilized to provide a robust benchmark challenge to the containment capability of the fume hood.

Test MaterialAppearanceParticle SizeDensity (g/cm3)Quantity Used
Sulfur hexafluorideColorless Gas~ 3.12Å diameter0.00624L / min
Methylene Chloride (DCM)Colorless liquid or gas~ 2.94Å diameter1.33 (l), 0.0035 (g)3 x 250 mL
Lactose MonohydrateWhite, crystalline powder<250 µm (≥99%)1.543 x 100g
For comparison, air has a density of approximately 0.0012 g/cm3

Table 1. Summary of test material attributes.

The initial factory acceptance test followed the standard ASHRAE110 and ANSI/AIHA Z9.5 testing protocols using Sulfur Hexafluoride(SF6)as the tracer gas. The following tests were performed:

1)an average airflow velocity at the face opening

2)small and large volume smoke tests

3) a tracer gas test.

The ANSI/AIHA Z9.5 standard testing for the tracer gas was followed, using the generally accepted 50 ppb threshold for factory acceptance.  The tracer gas used in the experiments was 99.95% pure sulfur hexafluoride, set at a flow rate of 4.0LPM.  The tracer gas ejector system is equivalent to that of the ASHRAE-110 standard ejector system.  Table 2 shows an overview of the test results.


Average Airflow Velocity (fpm)80.75 ± 4.95
Low Volume Smoke RatingGood
Large Volume Clearance Time (s)25
Average TracerGas Reading (ppb)Static0.00

Table2. Summary of general performance testing

It is possible to convert ppb of sulfur hexafluoride directly to units more commonly used in the industrial hygiene field through the following conversion factor:

1ppb = 5.98 µg/m3

Therefore, it is possible to calculate the release rate (inside) and escape concentrations (outside) of the sulfur hexafluoride during testing.  Table 3 shows the release rate concentration and the Short Term Exposure (STE) and Time Weighted Average (TWA) levels of the tracer gas during HAM testing.

Release rate concentration364,1612.18e6
Escape STEL2.8016.74
Escape TWA0.0150.087
Numbers are generated using the following values – CFM of unit tested @80.75 LFPM = 387.90; STE during 2.5 minutes sampling time; TWA based on STE and 8-hour work day.

Table3.  Summary of ASHRAE testing converted to common OEL values.

Surrogate Testing:

All sampling was performed in accordance with the following: best Industrial Hygiene practices; the guidelines published in Section II, Sampling, Measurement, Methods, and Instruments, of the Federal Occupational Safety and Health Administration (OSHA) Technical Manual; and the ISPE APCPPE Guideline.

All samples were collected using filters and portable pumps. Some pumps were stationary both inside and outside the containment area, others were mounted on the experimental subjects as in figure 4 below.  “Loaded” filters were then analyzed using validated analytical methods by a contract analytical laboratory accredited by the American Industrial Hygiene Association (AIHA).

In this study, lactose, an industry accepted surrogate, and methylene chloride (DCM) were utilized to determine the expected containment that a fume hood of this type would provide during manipulation of similar compounds during normal work practices.  These operations included weighing, dissolution and filtering.

A detailed description of the procedural steps used in this test is available from the manufacturer but is considered beyond the scope of this paper. Suffice it to say, tared weighing, dispensing, vacuum filtration, data recording, and cleanup were the key steps. Table 4 shows a summary of the quantities of surrogate materials manipulated, the concentration of powder generated inside the fume hood and the level of material that ‘escaped’ from the fume hood during operations.  As can be seen, for both of the surrogate materials utilized, no filters showed measurable quantities escaping.

OperatorSurrogateAmount Handled by OperatorAmount Collected on Outside Filters (escape) (µg)
1Lactose100 g<0.002
DCM250 mL<10
2Lactose100 g<0.002
DCM250 mL<10
3Lactose100 g<0.002
DCM250 mL<10

Table 4. Summary oftotal surrogate collected on filters outside fume hood.


During testing, a single filter was located inside the enclosure to measure the airborne concentration of lactose.  Since only a single filter was used, the concentration for each operator was assigned to be the same.  For DCM, volumes were measured at the start and end of the process for each operator. The difference in volume was used as a means to determine a worst case concentration of vapor (assuming total evaporation).5


Table 5 shows a summary of ‘Short Term Exposure’ (STE) and ‘Time Weighted Average’ (TWA) levels for each operator with both surrogates, both inside and outside of the fume hood.  These values are useful in determining the suitability of control devices as various ‘Operator Exposure Bands’ (OEBs) exist and are often determined by the end user. (N.B. The TWA is based on the concentration determined for the STEL and an 8-hour work day).

OperatorPowderConcentration Inside (STE) Max Outside (STE) (µg/m3)Concentration Inside (TWA) Max Outside (TWA) (µg/m3)
1Lactose5.64 (µg/m3)ND0.38 (µg/m3)ND
DCM61.90 ppmND4.12 ppmND
2Lactose5.64(µg/m3)ND0.31 (µg/m3)ND
DCM55.29 ppmND3.00 ppmND
3Lactose5.64 (µg/m3)ND0.33 (µg/m3)ND
DCM50.20 ppmND2.93 ppmND
ND – Levels were below reporting limit for analysis (2 ng for lactose; 10 µg for DCM)

                       Table 5.Summary ofsurrogate concentrations inside and outside fume hood.


Table 6 shows a summary of the total number of samples collected and exposures to surrogate materials for all operators.  Of the twenty-seven samples taken for each surrogate material for all operations, no samples showed detectable levels outside of the fume hood.

Powder TestedTotal Number of SamplesBreathing Zone SamplesArea Samples
Total NumberNumber With Detectable QuantitiesTotal NumberNumber With Detectable Quantities

Table 6. Summary of operator.


From all of the data presented, it can be seen that the Flow Sciences Saf-T fume hood series, when used with good laboratory practices offers exceptional containment of potentially harmful substances. In static testing, the fume hood contained tracer gas to an average level of 0.00 ppb, well below the ANSI/AIHA Z9.5 standard threshhold for factory acceptance testing.

In the dynamic version of the tracer gas testing, or HAM testing, again the unit performed very well, with escape of the tracer gas at an average of 2.80 ppb.  This suggests two things:

  1. That the fume hood provides exceptional containment even under situations more accurate of the desired use;
  2. That the static and dynamic tracer gas tests of Flow Sciences’ fume hoods are indicative of the level of containment provided.

During the surrogate testing, a more aggressive challenge was performed using two materials designed to mimic ‘real world’ operations.  With both the ‘powder’ and ‘vapor’ surrogate materials, the fume hood offered superb containment.  No filters from subjects or the test room showed measurable amounts of surrogates outside the fume hood.


An extensive evaluation of the containment capability of an FAF483655VAA from the Saf-T Flow series of fume hoods offered by Flow Sciences, Inc. was performed using both static and dynamic testing conditions.  In each of the tests performed, the level of material ‘escaping’ from the fume hood was significantly lower than concentrations generated inside.  This is particularly important when the vastly different physical characteristics of the test materials is considered.  Additionally, the static versus dynamic testing using the tracer gas showed excellent correlation, suggesting that either test is predictive of the containment capability of the fume hood.  Furthermore, the containment shown during the very aggressive surrogate powder testing show that this style of fume hood is capable of offering excellent protection to personnel during tasks of the nature described.

Overall, the Flow Sciences fume hood, when used in conjunction with good lab practices, is capable of providing workers with the protection they need for applications using solids, liquids and gases.6


  1. https://www.cdc.gov/niosh/docs/2012-147/pdfs/2012-147.pdf
  2. https://webstore.ansi.org/standards/ashrae/ansiashraestandard1102016
  3. http://ateam.lbl.gov/hightech/fumehood/doc/LBID-2561-HAM_SidebySide.pdf
  4. https://ispe.org/publications/guidance-documents/assessing-particulate-containment-performance
  5. The concentration of DCM was calculated based on the total volume loss of the liquid during each operator’s process and is assumed to be constant throughout the whole process.The total loss was converted to an average loss per minute based on duration of task.  Using Ideal gas volumes (22.4L/mol) a vapor volume per minute was calculated.  This was then converted to a ppm concentration based on the volume of air flowing through the fume hood.
  1. A full report containing all of the information presented here including the surrogate test protocol can be obtained by contacting Flow Sciences, Inc. at 1-800-849-3429.

Director of Product and Technology Development

Robert K Haugen  currently designs chemical laboratory containment equipment and develops new relevant technologies for Flow Sciences Inc.in Leland, North Carolina. He has also held positions at Kewaunee Scientific, Jamestown Metal Products, and St. Charles Manufacturing in similar capacities for 31 years. Previously, he did analytical chemical work at the University of Illinois (DNA, wastewater, and crop research) and Lawrence Livermore Labs in California (nuclear weapons research).

Dr. Haugen began his career as a curriculum writer for the Illinois Office of Education, developing texts on energy, urban management, and industrial pollution topics.

He received all his degrees from the University of Illinois in Urbana-Champaign, and is currently a member of the American Society of Heating, Refrigeration, and Air Conditioning Engineers, the American Chemical Society, and the National Fire Protection Association. He has participated in the development of both ASHRAE 110-1995 and the current 2016 update.

Fume Hood Fire Issues above the Duct Collar

Dr. Bob Haugen
Director of Product and Technology Development
Flow Sciences, Inc.


We have already looked at accidents inside fume hoods and posed several questions that might rush through one’s mind directly after a fume hood fire erupts 1.

From this earlier paper referenced above and an additional literature search we will examine the following issues in this second paper:

  • What construction and installation techniques must be observed while selecting and installing a fume hood that will reduce the chances of a fume hood fire spreading to the remaining lab space and possibly the entire building?
  • If a hood fire starts, should fume hood fans be switched off? (Issue unresolved in first paper)1
  • What kind of ductwork should be used for chemical fume hood exhaust?

The author reviews these key issues in the remainder of this paper.

Key Issues:

1) What construction and installation techniques must be observed while selecting and installing a fume hood that will reduce the chances of a fume hood fire spreading to the remaining lab space and possibly the entire building?


Any fume hood fire will interact with the room it is in. The suspended ceiling in such a lab is a key feature in determining how such a fire will spread. Flames may travel up through the fume hood into the duct system in this scenario. Let’s look at how such a ceiling is installed and what it is supposed to do during a fire.

Suspended ceilings made from fire-rated rectangular tiles are often used in lab construction as a way of retarding fire progression by preventing fires in a room from quickly spreading upward and affecting the room ceiling, which would accelerate the spread of fire to the floor above.

It has been found that such a ceiling must have all tiles in place to perform this function. Open rectangular spaces left during maintenance or replacement destroy the entire protective strategy.  Once through such an opening, fire and heat can rapidly spread horizontally and upward thereby propagating the flame to the immediate floor above.

If the fume hood liner material is breached with either cracks due to heat or dislodged plumbing access panels, very bad things happen! The hood fire can channel up the “chimneys” formed by the space between the outer steel shell of the fume hood and the hood liner material into the suspended ceiling cavity.

An actual dislodged access panel (Figure 5) is shown above. The panel is smaller than its circled opening and is fit into the cutout with a gasket. In this photo, the gasket has been dislodged by explosive force, causing the panel to fall through the opening, allowing a fire pathway upward.  In figure 6, a screwed-in panel larger than the covered opening resists explosive displacement.

In no case should interior fume hood plumbing access panels be smaller than the opening they cover. Gasketed material used to “seal” such openings should be avoided. More generally, access panels and gaskets should never be manufactured from a material which melts or can be distorted into a shape that can fall or be pushed through the hole they are covering.

Once a fire breaks through the hood wall liner material or access openings, it is free to move upward. Figure 7 shows two hoods soffeted into a suspended ceiling; an open gap above this hood will allow flames to enter the suspended ceiling cavity, ruining its effectiveness.  A finished suspended ceiling to the wall is preferred construction! (figure 8) This fume hood installation has a clear separation between ceiling and hood superstructure, preserving the fire retardant characteristics of the finished ceiling.

If a hood fire spreads into this suspended ceiling cavity, it will move horizontally relatively undeterred. Since many labs have “walls” that terminate at the suspended ceiling, these areas are often vast and untidy fire throughways.

NFPA 45 Section requires sprinkler systems in all NEW labs in accordance with NFPA 13. NFPA 13 states complete suspended ceilings should have sprinklers below such a ceiling. Incomplete ceilings, sometimes called “cloud ceilings”, may require sprinklers above and below the suspended ceiling line. Differentiation here is a bit unclear.  Obviously, the area above a ceiling should be properly protected by sprinklers, in a manner consistent with NFPA 13 and local code.

The general vulnerability of suspended ceiling design was summarized by Francis L. Brannagan as follows:

In the first edition of Building Construction for the Fire Service (1971), I pointed out the basic deficiency of this system: the loss or failure of one tile exposes the entire floor to the fury of the fire below. I was told by a U.S. General Services Administration (GSA) fire protection engineer that the GSA never built a building for its own account with this type of construction.”

To summarize, laboratory suspended ceiling design should not include an opening for the fume hood superstructure to “fit through”. A complete suspended ceiling should always be placed above the entire lab, including the fume hood superstructure. Such a complete suspended ceiling will resist flames traveling from the inner containment area of a fume hood into the painted steel outer shell where they can easily “chimney up” past the fume hood superstructure.

For this reason, contractors should never use the fume hood superstructure as an anchoring point for a suspended ceiling in a lab. A gaping hole above the hood in the suspended ceiling results. This condition obviously exacerbates the spread of any fume hood fire through the suspended ceiling space.

There is at least one very notable example of how suspended ceiling spaces can become involved in quickly spreading lab fires. It happened in 2012 in Tulsa Oklahoma:

The historic Barnard School Building went up in flames about 5 a.m. on September 5. When firefighters arrived, the building exploded, rocking midtown Tulsa and sending eight firefighters to the hospital.

After a week-long investigation, officials said the fire and explosion resulted because of “construction related to the installation of an exhaust vent in the lab area,” according to a news release.

The explosion occurred because the fire had been smoldering in the void between the chemistry lab ceiling and the floor of the room and hallway above, the release said.

Investigators said the fire migrated north under the hallway floor into the classroom, and the crawl space below where it vented from the classroom window. The resulting smoke explosion or “backdraft” occurred when oxygen was introduced into the area by the firefighters entering the room to extinguish the fire.

News 6 Tulsa 14 September 2012.

2) If a hood fire starts, should fume hood fans be switched off or fire dampers be activated? (Issue unresolved in first paper)1

First, we go to the latest NFPA 45 standard to determine if dampers should be automatically closed in hoods in the event fire is present in the duct:

NFPA 45 clearly prohibits fume hood fire dampers. In addition, a clause was added this year ( stating flow control dampers added for other reasons in a fume hood exhaust duct must fail open.

On the issue of exhaust ventilation being turned off in case of a fire, NFPA 45 section 7.5.11 states:

While NPPA does not state why this requirement is so strongly set forth (in all cases shall is used), there are many well-known realities in play here:

  1. Stopping flow through a fume hood exhaust duct during a fire would insure all the combustion byproducts would erupt back into the lab area. (carbon monoxide, aromatic hydrocarbons, soot, other “bad actors”.
  2. In a hood fire, a functioning fume hood exhaust offloads heat as well as fumes. In the short term, an exhaust cutoff would increase the temperature inside the containment cavity assuring faster compromise of this structure.
  3. Escaping lab personnel need fresh air, which will be drawn into the lab in direct proportion to the exhaust that is drawn from it.
  4. To some degree, this question has almost become academic as fewer and fewer fume hoods are specified with fan on-off switches in the first place.

Given these issues, we conclude fume hood exhaust shall not be switched off in a fire situation!

3) What kind of ductwork should be used for chemical fume hood exhaust?

Again NFPA 45 speaks, albeit equivocally, to this question:

While hood interiors and ductwork are limited to a flame spread <25, ductwork must also be compatible with conveyed materials (

If lab designers were hoping to be given specific help on duct type by NFPA 45, they would have been severely disappointed by section Particularly in large projects with diverse labs, this rather vague section on duct compatibility assumes chemists all do the same thing and there is a duct type that is omni-resistant. Neither of these assumptions are true.

Ductwork made from different materials behave differently. Here are examples:

1) Stainless steel ductwork is great, except with halogen acids like HCl (one of the most common reagents).

2) PVC ductwork is great for acidic fumes like HCl (g), but certain types soften at 250o

3) Galvanized steel ductwork (the least expensive option) maybe acceptable for milder applications unless corrosion scenarios become present when the quantities of exhausted corrosives are dramatically increased by some new application.

How can an Architect/Designer assure a building’s safety when ducts may cease to conform with section of NFPA 45 as new chemists, projects, and missions change routinely used chemicals being exhausted into original ductwork within the lab building?

Flow Sciences always asks application questions of our customers exactly because of issues like these noted above. What is your application? How much reagent(s) are exhausted each week? Are you considering energy conservation by reducing exhaust volumes? What are the chances your applications will significantly change?

Obviously, when manufacturers ask such questions, we protect ourselves and our customer from receiving the wrong product for the application.  Building-wide exhaust issues are always a much larger question generally abandoned at the doorstep of building maintenance. As VAV and other low volume technologies become retrofitted, further reducing exhaust flow for fume hood procedures, corrosive exhaust concentrations will increase. Ducts installed for more dilute fume concentrations may become severely challenged for this reason alone!


1) From a fire safety standpoint, a well-designed fume hood must have a containment cavity built with materials having a flame spread < 25 using ASTM E84.

All interior access cutouts should be covered with liner material with a similar low flame spread. Side wall interior access panels must be larger than the cutout and held in place with screws rather than gaskets, unless said gasket will not burn, melt, or come loose in a fire.

In addition to this precaution, the hood must never be installed as part of the suspended ceiling support system.  A suspended ceiling should go above a fume hood and never through it!

2) A fume hood exhaust system should never be shut down during a hood fire event. Dampers should not be closed.  Not automatically, not manually.

NFPA 45 is clear on this issue. The effects on lab personnel and room fire Involvement rate of disabled exhaust systems are typically worse than if the system is allowed to run.

3) Chemical exhaust ducts should have an ASTM E84 flame spread < 25.

While any duct must be compatible with materials being exhausted, facilities should record the duct types used so when fume hood applications change with time, new uses may be checked for compatibility with the existing ducts. Where necessary, non-zero flame spread ductwork must be fire shielded as described in NFPA 45. Commonly used duct materials are stainless steel, PVC, and galvanized steel. Each material has limitations and advantages which may be reviewed with respect to lab exhaust use profiles.


In summary, we have seen that fume hood fires must be seen in the context of what goes on above the hood as well as in it. Fans, ductwork, and the maintenance of a complete suspended ceiling all play a role in preventing serious laboratory fires.


  1. Fume Hood Fires, Robert Haugen, Flow Sciences White Paper, 8/2018, https://flowsciences.com/fume-hood-firessmoke-heat-and-finally-illumination/
  2. Making Sense of Laboratory Fire Codes, Richard Palluzi, AIHCE Journal, pp 54-58
  3. University of Hawaii Fined $115,000 for lab explosion, C&EN News, Sept 29,2016
  4. Overview of the International Mechanical Code, International Code Council, 2018, https://www.iccsafe.org/products-and-services/i-codes/2018-i-codes/imc/
  5. https://www.fireengineering.com/articles/print/volume-158/issue-4/departments/the-ol-professor/suspended-ceilings.html, FRANCIS L. BRANNIGAN, SFPE (Fellow), the recipient of Fire Engineering’s first Lifetime Achievement Award, has devoted more than half of his 63-year career to the safety of firefighters in building fires. He is well known as the author of Building Construction for the Fire Service, Third Edition (National Fire Protection Association, 1992) and for his lectures and videotapes. Brannigan is an editorial advisory board member of Fire Engineering.
  6. https://www.huffpost.com/entry/chemistry-fire-video-lab-sprinklers_n_3314085
  7. Flow Sciences floor mount fume hoods
  8. https://publicsafety.tufts.edu/ehs/fire-safety/
  9. http://www.expertconstructioninc.com/acoustical.html
  10. This is a photo of the Flow Sciences Saf T Flow fume hood sidewall access panel. Other manufacturers emulate this design.

Robert K Haugen currently designs chemical laboratory containment equipment and develops new relevant technologies for Flow Sciences Inc. in Leland, North Carolina. He has also held positions at Kewaunee Scientific, Jamestown Metal Products, and St. Charles Manufacturing in similar capacities for 31 years. Previously, he did analytical chemical work at the University of Illinois (DNA, wastewater, and crop research) and Lawrence Livermore Labs in California (nuclear weapons research).

Dr. Haugen began his career as a curriculum writer for the Illinois Office of Education, developing texts on energy, urban management, and industrial pollution topics.

He received all his degrees from the University of Illinois in Urbana-Champaign, and is currently a member of the American Society of Heating, Refrigeration, and Air Conditioning Engineers, the American Chemical Society, and the National Fire Protection Association. He has participated in the development of both ASHRAE 110-1995 and the current 2016 update.

The Galaxy of Containment Devices

Robert K. Haugen, Ph.D.

Director of Product and Technology Development

Flow Sciences, Inc.


The galaxy of laboratory containment devices is incredibly diverse.


While many segments of this industry have developed their own categories of classification 1, no overarching system of categories has ever been developed for the entire lab containment equipment industry.


We offer such a model here and invite others to reflect upon it and offer comments on any refinements you deem necessary. The most powerful enemies of any model are time and discovery.


Nevertheless, here is our 2019 attempt to conquer the galaxy!



We believe most lab containment products can be fit into one of these five categories: 1) Chemical Fume Hoods, 2) Powder / Pharmaceutical Containment Devices, 3) Biological Safety Cabinets, 4) Special Purpose Glove Boxes, and 5) Local spot ventilation.


Remember, these five areas are broad categories. Depending upon the given area, many sub-categories are likely. We examine each category closely below:


  1. Chemical Fume Hoods:

These units are almost always permanently installed in a certain location inside the laboratory. Their main purpose is the containment of vapors created during chemical reactions. Exhaust is typically carried out of the building and into the air via an exhaust stack. In limited circumstances, this exhaust may be filtered and subsequently exhausted or sent back into the laboratory.


A chemical fume hood is defined in ASHRAE 110-2016 2 as “a box-like structure enclosing a source of potential air contamination, with one open or partially open side, into which air is moved for the purpose of containing and exhausting air contaminants. A laboratory hood is generally used for bench-scale laboratory operations but does not necessarily involve the use of a bench or table.”



a) Counter top exhaust hoods:

These hoods are the most typical chemical exhaust unit and have many applications. They are almost always permanently installed in one location.

b) Floor-mount & purpose-built large exhaust units


These large devices usually serve as containment housings for large machinery and processes. These containment devices are so large that their exhaust requirements far exceed standard fume hood specifications. Such units may have filtered input air and exhaust and may be designed for production level distillation/refluxing, portable virulent disease treatment, or kilo-scale applications.


The writer presents the following as examples of Large Equipment Enclosures:

2.  Powder, Pharmaceutical Containment Devices:

The devices in this category are primarily used in the formulation and analysis of dry, finely divided pharmaceutical powders. Because such applications under the wrong conditions can easily create a dangerous environment for process workers and scientists, surrogate powder testing in areas within 25 feet of such containment structures are typically specified at or below 10 nanograms per cubic meter.

Designing such a pharmaceutical containment device with unfiltered exhaust air leaving the building through exhaust stack is virtually never done.

These pharmaceutical containment devices come in a wide variety of sizes, filter options, and materials of construction. Flow Sciences estimates over 6,000 “standard” products are available considering these options alone!

As noted in an earlier article10,this widely divergent collection of containment units may also be linked together into process arrays to keep HAPI’s isolated during research or production procedures.

3.  Biological Safety Cabinets:


Biosafety cabinets are defined as “an enclosed, ventilated laboratory workspace for safely working with materials contaminated with (or potentially contaminated with) pathogens requiring containment.” Several different types of BSC’s exist, differentiated by the degree of biocontainment required.4 Most biosafety cabinets send exhaust through HEPA particle filters and return this air to the laboratory or exhaust it outside. Without getting too far into the weeds, three classes of BSC’s exist:


a) Class I:


These cabinets provide personnel and environmental protection but no product protection. In fact, the inward flow of air can contribute to contamination of samples. Inward airflow is maintained at a minimum velocity of 75 ft. / min (0.38 m/s). These BSCs are commonly used to enclose specific equipment (e.g. centrifuges) or procedures (e.g. aerating cultures) that potentially generate aerosols. BSCs of this class are either ducted (connected to the building exhaust system) or unducted (recirculating filtered exhaust back into the laboratory).

b) Class II:


Class II cabinets are the most commonly used in clinical and research laboratories. These cabinets provide personnel and product protection since makeup air is HEPA-filtered. There are five types of these units: Type A1, Type A2, Type B1, Type B2 and Type C1. Each type’s requirements are defined by NSF International Standard 49. About 90% of all biosafety cabinets installed are type A2 cabinets.

Principles of operation use motor driven blowers (fans) mounted in the cabinet to draw directional mass airflow around a user and into the lower interior front air grille – protecting the operator. The air is then drawn underneath the work surface and back to the rear vertical baffle, then up to the top of the cabinet where it passes through the high efficiency particulate air (HEPA) filters. A column of HEPA-filtered air is then blown downward, over products and processes to prevent contamination. Air is also exhausted through a HEPA filter, and depending on the Type of Class II BSC, the air is either recirculated back into the laboratory or pulled by an exhaust fan through duct work and expelled from the building.


c) Class III:


The Class III cabinet, sometimes called an isolator, is generally only installed in settings where contamination is particularly undesirable. It is specifically designed for work requiring USP requirements for sterility under chapter 1211. System shown below uses an HO2 generator for decontamination. Gloves attached to the front prevent direct contact with hazardous materials.

4) Special Purpose Glove Boxes

Glove boxes are also used in many divergent scientific areas not associated with the tightly-defined discipline of Biosafety and NSF 49.


a) Hybrid Glove Boxes

Flexible hybrid units which add minimal air flow and removable front panels to the Biosafety model have been used in several different pharmaceutical applications involving High Potency Active Pharmaceutical Ingredients (HPAPI’s), including compounding and sampling.

b) Specialized atmospheric glove boxes with very limited exhaust

Many chemical and radiological applications require either very dry or oxygen-free conditions. This condition can be achieved with either a pure nitrogen or inert gas atmosphere. Such applications include pyrophoric substances, hygroscopic materials, and radioactive metals that oxidize aggressively. As a consequence of such a sealed environment, containment is also achieved.

c. Integrated Glovebox arrays for HPAPI Processing

With HPAPI (High Potency Active Pharmaceutical Ingredients) or API materials, it is frequently advantageous to link process-specific modules together so an entire process of formulization can take place inside an isolated, multi-step environment. The number and types of such modules that can be linked together is virtually without limit.

5) Local Exhaust Ventilation:

Several types of localized ventilation serve the research needs of the 21st  Century. The functional caveat of these technologies is that they are an inexpensive technique for managing less toxic fumes or heat using an exhaust source in an area not confined by walls or a sash. As such, their “containment” effectiveness is very limited.

These units show effective localized removal of heat and non-toxic odors with reduced exhaust requirements compared to chemical fume hoods. Canopy hoods and funnel exhaust systems are examples of this containment type.


a) Canopy Hoods:

Canopy hoods are effective with high temperature fumes in close proximity to the canopy. They are far less effective if fumes are emitted at room temperature or more than 18” vertically away from the canopy.

These systems are most effective with very small quantities of fumes where the exhaust port can be maneuvered very close to the fume emission point. If these conditions are not met, these devices will not be effective.


Another Model Reveals Similar Containment Groups!


While I was working on this paper, Ray Ryan and myself were also trying to sort containment groups by function and protection.This was being carried out to support the expanding need for SEFA standards (SEFA is Scientific Apparatus and Furniture Association) for newly emerging products.


Here is an array of products defined by whether devices protect personnel, product, or both.

Over this model, I have circled the categories where Flow Sciences has products. Again, we are covered in three of the four product categories identified, only missing devices that protect products, but not personnel. This diagram confirms our company’s commitment to protect personnel, while offering us the opportunity to develop new products which keep products clean while not protecting personnel (uncircled tree). Many electronic component manufacturing fields emphasize this uncircled category.

Summing It Up:

There is a huge variety of laboratory containment devices. We can group these devices into either five or four categories depending on which model of classification we use. One model sets forth types of commonly grouped containment devices. The other model classifies containment devices that protect product, personnel, or both.

Containment groups are summarized below first by established groups, and second by product/personnel protection characteristics.

Cat #Cat. NameProduct MarketsContainment Level FSI Products
Ed. & Gen Chem.PharmaNuclearBio
Established Areas Model
1Chem. Fume HoodsXXXX< 0.05 PPM 1Y
2Powder containment XX <0.05 PPM 1Y
3Biosaf. CabXX XNSF Listed 2Y,(Cl.1 only)
4Special Purp Glv. Boxes XXX< 0.05 PPM 1, 5Y
5Local non contained ventilationX   Various 4, 5Y
What’s Protected Model
1Personnel ProtectionXXXX< 0.05 PPM 1Y
2Product Protection (6)   (Ag. & Chip)Iso Class 5 7N
3Personnel & Product Protection XXX< 0.05 PPM 1, ISO Class 5Y

  1. Defined by ASHRAE 110 2016; control Level set in AIHA Z 9.5
  2. Pass all tests NFF 49 or equivalent
  3. For localized canopy and funnel exhausters, there are no US standards for containment
  4. ASHRAE 110-2016
  5. Surrogate powder testing also frequently done with different levels of acceptance
  6. Since this class of product blows air outward into the lab, it does not protect the worker but does bathe the product in HEPA filtered air, keeping it free of contaminants.
  7. Iso Class 5, an ISO class 5cleanroom is designed to allow no more than 3,520 particles equal to or larger than 0.5 microns per cubic meter of air. This equates to a Class 100 cleanroom under the Federal Standard 209E, which allows for 100 particles (0.5 microns or larger) per cubic foot of air.

Any company in search of a mission statement or identity may find the “FSI Products” column in the chart illustrative. It will show areas of competence and involvementin the containment. Conversely, it highlights areas of non-involvement which may also be new market opportunities.

Remarkable! A search to develop a market model has led to a way to define mission and highlight growth opportunities. This galaxy gives back!




  1. Biosafety cabinets, for instance
  2. ANSI / ASHRAE 110-2016, American Society of heating, refrigeration, and Air Conditioning Engineers, p.4
  3. Flow Sciences, Haugen, Critical Considerations when Selecting a Vented Balance enclosure, 2018, P. 2
  4. https://en.wikipedia.org/wiki/Biosafety_cabinet
  5. The Eagleson Institute https://www.eagleson.org/products/productdetails/?id=31
  6. http://fumehoodstore.blogspot.com/2014/01/largest-fume-hood-genie-scientific-has.html
  7. Installed isolation area in pharmaceutical lab (Flow Sciences)
  8. When connecting a FS Fan/Filter to house exhaust, Flow Sciences recommends the use of a Thimble Connection to provide safe exhausting of the Fan/Filter Housing. Since each Fan/Filter Housing has a built-in fan downstream from the filter, the connection should be made with the Flow Sciences’ Thimble Connection which has been designed to be slightly larger (5″ID) than the discharge duct from the Fan/Filter Housing which is 4″ OD. The thimble is then fitted with 4″ID flex hose which runs to the general exhaust. The house exhaust should pull more CFM that the Fan/Filter is exhausting. For example, if the Fan/Filter Housing is exhausting 100 CFM, Flow Sciences recommends the General Exhaust be set to 115 CFM. The purpose of this is to prevent fluctuations in the general exhaust from adversely affecting the performance of the enclosure.
  9. flowsciences.com

Designing and Testing Containment Systems for High Potency Active Pharmaceutical Ingredients,  Dr. Robert K. Haugen, Director of Product and Technology Development), 2018, Flow Sciences Inc.; https://flowsciences.com/designing-testing-containment-devices-used-high-potency-active-pharmaceutical-ingredients/

Director of Product and Technology Development

Robert K Haugen  currently designs chemical laboratory containment equipment and develops new relevant technologies for Flow Sciences Inc.in Leland, North Carolina. He has also held positions at Kewaunee Scientific, Jamestown Metal Products, and St. Charles Manufacturing in similar capacities for 31 years. Previously, he did analytical chemical work at the University of Illinois (DNA, wastewater, and crop research) and Lawrence Livermore Labs in California (nuclear weapons research).

Dr. Haugen began his career as a curriculum writer for the Illinois Office of Education, developing texts on energy, urban management, and industrial pollution topics.

He received all his degrees from the University of Illinois in Urbana-Champaign, and is currently a member of the American Society of Heating, Refrigeration, and Air Conditioning Engineers, the American Chemical Society, and the National Fire Protection Association. He has participated in the development of both ASHRAE 110-1995 and the current 2016 update.

How Does the FSI Fume Hood Stack up on The Top Ten Lab Worker Needs?


Lab Manager magazine1 recently published a feature entitled Survey Says. In this article was a section called What You Need to Know Before Buying a Fume Hood.”   Ten factors were named in over half the lab managers surveyed. We will review and analyze these factors and discuss how Flow Sciences addresses them. Whatever we’re doing, most of our customers seem to like it a lot!


In the December 2018 Lab Manager, the article Survey Says, cites the top ten things managers look for in a chemical fume hood:

We decided to look at this “top ten list” and see how the Flow Sciences fume hood stacks up. We discovered that these sought-after qualities really lead to a shopping list of features, most of which are standard on the Saf T Flow hood…..read on!

Top Ten features reviewed:

1 – Performance of Product:

Before performance can be discussed, Flow Sciences always asks our customer what application is being undertaken in the fume hood.

This is very important. Most containment manufacturers have valuable and worthwhile tests they perform on standard product. These tests may be generally useful, but not relevant if the customer, for example, requires a hood with a larger than standard sash opening. Or if the chemicals being used in the hood have unique characteristics that require special linersor wash-down systems.

Many lab managers may not realize that these factors, if not considered, will lead to poor performance or dangerous conditions. Once special needs are considered, Flow Sciences can provide testing information on standard product, or run tests on the modified hood and document the effectiveness of the modifications.

Both of the non-standard products shown above had outstanding containment both on ASHRAE 110-2016 and the “HAM” test developed by Tom Smith of 3-Flow and Lawrence Berkeley National Lab 2.

2 – Durability of product.

Flow Sciences believes fume hoods should have a minimum serviceability of twenty years. If lightly used, most fume hoods made in the US will last this long. If hoods must be moved or modified within this time period, or if they are heavily used, or used for applications different than those specified, they may not last one year, or never work at all!

We illustrate below several design “weak points” of many common fume hoods sold today and better ways to design a more robust product.

        A – Fume hood sash system. Such a system should work reliably, need few service adjustments, and never break down. Shown below are examples of an inferior and a good sash counterbalance system:

        B – The fume hood support frame should be a stand-alone heavy-gauge system! If equipment collapses or a fire breaks out, such a system prevents hood collapse if key liner panels get broken!

        C – Flexible Plumbing is important today. It used to be plumbing in fume hoods was hard- piped. Such plumbing had solders which could rattle loose in shipping and leak when hooked up to pressurized services in the lab. Newer plumbing is flexible with no welds at all! This system hooks up quickly to mated pressurized fittings in the field. Also this flexible system allows service gasses to be changed or modified if research requirements change!

        D – Flexible Counter Top Design! This top actually slides out for replacement or repair. The lift-up airfoil allows cords to be routed to outlets without resting on the airfoil top where the sash will run into cords every time it is closed!

3 – Safety and health features. The primary purpose of a chemical fume hood system is user safety. Features of design and construction should work as a system to assure this. We recommend any fume hood demonstrate safety by compliance with at least five published standards:


        A – ASHRAE 110 2016. The use of a gas diffuser inside the fume hood and a mannequin with a breathing zone detector to assure that less than 0.05 ppm (Parts per million) of tracer gas gets into the breathing zone of the mannequin during a five-minute test.

        B – The Human as Mannequin Test. Cited earlier, the test uses a gas diffuser and simple lab equipment inside the fume hood which is manipulated by a test subject with a breathing zone sensor. A pass/fail reading of less than 0.05 PPM (parts per million) should again be used.

        C – The UL 1805 Standards. Widely accepted in the US and Canada, UL 1805 sets forth both a physical testing regimen for safety glass, epoxy work tops, and liner materials and an outline for internal wiring of the fume hood. Most major fume hood manufacturers comply with these standards, products in conformity must have a UL 1805 compliance tag visible somewhere on the fume hood exterior.

        D – Surrogate Powder Containment and Balance Stability data for fume hoods involved in pharmaceutical weighing and dispensing procedures. More and more fume hoods are involved in procedures where pharmaceutically active compounds are manipulated. These materials do not diffuse in the same way vapors and gasses do. If such materials are used in a fume hood, containment data regarding powders must be provided using an appropriate test room and collection equipment. Procedures should reflect the types of manipulation to be used by the customer.

        E – ISO 9001:2015 Certification of the manufacturing facility. All materials and procedures must be trackable and verifiable to assure construction material, flame spreads, certifications, and other assembly issues relevant to the safety and durability of the equipment are solidly documented.

4 – Easy to Clean. Any chemical fume hood should be easy to clean. For scrupulous cleaning, fume hood components must be chemically resistant and easy to access for cleaning.


A – Chemical resistivity. All paints must be certified against the SEFA (Scientific Apparatus Manufacturers’ Association) standard set forth in SEFA 8-M-2010. In this standard, paints are tested against scratching, abrasion, and chemical resistivity. Liners must meet NFPA Class A flame spread requirements.

        B – Access to all exposed surfaces. All exposed surfaces inside the fume hood containment area must be completely accessible for cleaning. Illustrations below show how this is achieved in the Flow Sciences product:

5 – Ergonomic ease of operation. Several features help satisfy this criterion. The glass top panel allows complete vision of the hood interior. Great for tall distillation columns or thermometers on tall equipment. The chain drive sash is easier to move up and down than any other system and does not wear out. Either bright T-5 fluorescent lighting or high output LEDs are available for clear vision of the very deep 25 7/8” hood interior. Base cabinets or a table for seated work are available. We also have built in a very stable anchoring system for scaffolding. All our standard hoods come with this anchoring system. To maximize flexibility needs inside a lab, Fume hoods are available in 1’ width increments from 3’ to 8’.

6 – 7 – 10 – Value for Price Paid, Low operating costs, Cost of ownership


These three lab manager survey questions are so interwoven, that the author will lump them together for analysis. The sixth and seventh issues, value and operating cost, cannot accurately be discussed as separate items. When one purchases a fume hood, the hood purchase price is just the tip of the iceberg4 as far as operating cost.

As seen in the graph above from an article written last year, a “low cost” hood inherently consumes more energy than a hood designed to save energy by exhausting less air. Over just five years, the engineered hood (red line, higher first cost) has consumed $30,000 of energy, while the low cost hood has consumed $64,000! (This is not a good way to save $2,700 on purchase price!)


In fact, even asking someone to evaluate hood price/value and energy savings separately is a fatal error! The author invites anyone interested to read the cited article and the various mathematical inputs that fostered the graph shown above.


So value, properly evaluated, must include energy efficiency!


Let’s now look at the tenth survey questioncost of ownership.  This tenth item on Lab Managers survey list is clearly also part of the discussion we are now having regarding value and energy efficiency. The author regards valueand energy efficiency as inputs into discerning cost of ownership!


Here’s the headline: Cost of ownership will always favora contemporary, engineered energy-efficient fume hood! As an example, the Flow Sciences energy-efficient hood has remarkable containment down to 60 FPM at an 18” sash opening. Check out these containment graphs:

6’ Fume hood containment at 60, 80, and 100 FPM:

The bottom line? This fume hood persistently shows comparable very low control levels on the ASHRAE 110-2016 test regardless of face velocity within the 60 FPM to 100 FPM range!

FINALLY, a hood that can operate at very low face velocity without diminished containment capability! Engineering and design make a difference. Engineering and design save exhaust. Engineering and design yield the lowest cost of ownership!

8 – Service and Support. This issue is really important and is underrated on the list by the rankings provided. A lab safety item like a fume hood cannot even begin its life without being “checked out” after installation to be sure it is functioning properly. One must use knowledgeable resource people who can compare how a fume hood is supposed to work with how it is actually Knowledgeable service at Flow Sciences begins with “ask Robin”. Through this contact person, a high level of service and customer support are achieved by referencing telephone questions to the appropriate engineer. This service has received the highest customer reviews. Our 800 service number is part of the fume hood label!

This may be why our best customers keep coming back with additional orders, while praising our customer service! 6

9 – Warranty.  All mechanical and electrical components of the Saf T Flow fume hood are guaranteed against defects for a period of one year from the date of receipt. A warranty form and card are included with manuals for each unit sold.


In addition to this rather limited issue, Flow Sciences has always “gone the extra mile” with our customers on answering questions, providing information on replacement parts, or sending out safety videos or other materials that may have been lost after the product was delivered and installed.



The Flow Sciences Saf T Flow fume hood is a laboratory safety product. We have shown here how it addresses laboratory managers’ ten top criteria for a successful safety product. These fume hoods perform the tasks lab managers identify as important. They are durable, safe, easy to maintain, and ergonomically designed. They are of very high value and exhibit a very low cost of ownership compared to similar products. These fume hoods are impressively warranted to do their intended job. And Flow Sciences has an exemplary record of post-sale customer support.


As long as our customers keep smiling, we will keep providing the finest containment equipment in the industry!



  1. Lab Manager Magazine, 12/2018, p57
  2. Side-by-Side Fume Hood Testing, Human-as-Mannequin Report, 2004, California Energy Commission, Sartor, Sullivan, Bell, Smith, et.al., p9
  3. On June 17, an explosion in a chemistry lab at the University of Minnesota injured graduate student Walter Partlo. He was making trimethylsilyl azide, starting with 200 g of sodium azide. The incident originated in lack of hazard awareness, school representatives say, and the department response focuses on identifying hazardous processes and communication. http://cenblog.org/the-safety-zone/2014/07/more-details-on-the-university-of-minnesota-explosion-and-response.
  4. The Fume Hood Product Life Cycle, A Cost of Ownership Analysis, Haugen, 2018, https://flowsciences.com/fume-hood-product-life-cycle/
  5. Typical email praise: ” I just wanted to reach out to let you know that I have dealt with many technical support and parts associates in our industry over the years and none have been more helpful or pleasant than Robin Williams. I have never been disappointed in the high quality service that Flow Sciences provides. I look forward to meeting both you and Robin at the upcoming CETA conference in Memphis.

Have a great day!”

Director of Product and Technology Development

Robert K Haugen  currently designs chemical laboratory containment equipment and develops new relevant technologies for Flow Sciences Inc.in Leland, North Carolina. He has also held positions at Kewaunee Scientific, Jamestown Metal Products, and St. Charles Manufacturing in similar capacities for 31 years. Previously, he did analytical chemical work at the University of Illinois (DNA, wastewater, and crop research) and Lawrence Livermore Labs in California (nuclear weapons research).

Dr. Haugen began his career as a curriculum writer for the Illinois Office of Education, developing texts on energy, urban management, and industrial pollution topics.

He received all his degrees from the University of Illinois in Urbana-Champaign, and is currently a member of the American Society of Heating, Refrigeration, and Air Conditioning Engineers, the American Chemical Society, and the National Fire Protection Association. He has participated in the development of both ASHRAE 110-1995 and the current 2016 update.

Perchloric Acid Fume Hoods: Questions & Answers



No technology in fume hood design is more unique or stranger than the perchloric acid fume hood. This white paper describes the utility of perchloric acid in many modern applications. While perchloric acid is useful in chemistry, it is remarkably hazardous in unique ways. These hazards must be recognized, designed for, and supported with appropriate applications, equipment, and regular maintenance.


After reviewing this acid and its uses, the writer will examine questions regarding proper fume hood use and controversies which appeared recently in a Linkedin discussion of these matters by a variety of scientists involved with perchloric acid research. He will then suggest different approaches for addressing these questions.

Perchloric acid, HClO4,can be symbolized in a variety of ways as shown above. It is a liquid at room temperature with a melting point of -17OC and boiling point of 203OC.

A major part of perchloric acid is the perchlorate ion, [ClO4]-1. This ion is very unstable and can, depending on reaction conditions, give off oxygen, free radicals, or combine with other reactants containing carbon to form organic peroxides.

An organic peroxide is a carbon-based compound containing a “peroxy” group (two oxygen atoms joined together -O-O-). It is the double oxygen of the “peroxy” group that makes organic peroxides both useful and hazardous. The peroxy group is chemically unstable, and can decompose with varying degrees of severity.1   Many times these peroxides are explosive.


Today, ”perchloric acid is mainly produced as a precursor to ammonium perchlorate, which is used in rocket fuel. The growth in rocketry has led to increased production of perchloric acid. Several million kilograms are produced annually. Perchloric acid is one of the most proven materials for etching of liquid crystal displays and critical electronics applications as well as ore extraction and has unique properties in analytical chemistry.


In addition, it is a useful component in etching of chrome.”2

Perchloric acid in industry and in fume hoods:

Perchloric acid has a brutal history of causing industrial accidents:


“On February 20, 1947, in Los Angeles, California, 17 people were killed and 150 injured when a bath, consisting of over 1000 liters of 75% perchloric acid and 25% acetic anhydride by volume, exploded. The O’Connor Electro-Plating plant, 25 other buildings, and 40 automobiles were obliterated, and 250 nearby homes were damaged. The bath was being used to electro-polish aluminum furniture. In addition, organic compounds were added to the overheating bath when an iron rack was replaced with one coated with cellulose acetobutylrate. A few minutes later the bath exploded.” 7

While not a lab event, this tragic scene highlighted the magnitude of the danger of perchloric acid reactions with organic chemicals.


To guard against other such events, perchloric acid fume hoods and related equipment allow the safer laboratory use of this chemical in smaller quantities. Perchloric acid fume hoods use a wash-down system daily or after a procedure is complete. In most cases, this requires emptying the fume hood and running a hood-ductwork wash-down cycle of at least ten minutes. Ventilation elements of this process are shown below:

In improperly maintained perchloric acid fume hoods, white powder may appear inside the fume hood or ductwork as shown below:

Such organic perchlorate salts or organic peroxide powder residue may be explosive. Once chemical hazard specialists are summoned to analyze similar situations, they may empty the hood, run a back baffle wash-down cycle, and then gently remove any material remaining within the containment area with a sponge and water, discarding the rinse water down the wash down trench at the hood back. Other more serious procedures may be applied depending on the diagnosis of the material and other involved elements of the duct system (like ductwork problems in frame 3 above).


What the literature states about perchloric acid fume hood hazards:

  • ANSI-AIHA Z9.5 2012 addresses this acid in perchloric fume hoods:

Other sections of AIHA Z 9.5 address in detail how ductwork must be made of chemically resistant materials, washed down, and not ganged together with other types of fume hoods.

The 2012 standard position on perchloric acid use shown above is much more permissive than the 2003 version of the same procedure outline which is stated below (slightly different number for same section):

Note that the newer standard does not regard perchloric acid as a peroxide fume-former at lower temperature if the concentration is less than 72% because its vapor pressure in lower concentrations is too low to cause fume release at room temperature. The new standard primarily focuses on the acid’s inherent vapor release properties and reactions known to be hazardous in lower concentrations.

We need to understand the implications of this important change. The author reviewed other sources of information regarding lower temperatures and peroxide presence.

It turns out, other sources in the literature significantly differ with the “new” section 3.2.5 in their view of perchloric acid procedures and which ones pose a threat to safety.

  • The University of Calgary states a more cautious approach to perchloric acid at concentrations less than 72%. In its formal perchloric acid procedure5, the following is noted:


”Perchloric acid (60-72%) acts and reacts with alcohols and certain other organic compounds to form very unstable perchlorate esters at room temperature.”


Other reactions with lower concentrations of perchloric acid are also mentioned in this document.



  • The University of Illinois has published a background paper on its website citing three known conditions where concentrations of perchloric acid less than 72% can cause problems 6.
    • Perchloric acid forms an azeotrope with water at a concentration of 72.5% perchloric acid. Therefore, aqueous solutions do not form anhydrous perchloric acid by evaporation. However, dangerous anhydrous perchloric acid can form when an aqueous solution is subjected to strong dehydrating conditions such as exposure to concentrated sulfuric acid, acetic anhydride, or phosphorous pentoxide.
    • At elevated temperatures, vapors from perchloric acid can condense on surfaces in the ductwork of the hood, where they form perchlorate salts that are often highly shock-sensitive and that pose a serious explosion hazard.
    • Perchloric acid reacts with alcohols and certain other organic compounds to form highly unstable and explosive perchlorate esters.
  • In A Guideline for the Use of Perchloric Acid and Perchloric Acid Fume Hoods, The British Columbia Ministry of Energy and Mines concludes: A fume hood designated for the use of perchloric acid must be used when handling or performing a reaction with perchloric acid. There are risks of fire and/or explosion should perchloric acid contact incompatible materials or perchloric acid vapors, released by the heating of perchloric acid, condense and crystallize on laboratory surfaces. Using a proper perchloric acid fume hood with a wash-down system is imperative in preventing inadvertent contact with incompatibles and the formation of perchlorate salts. Perchlorate salts are highly explosive and sensitive to shocks and vibrations, including the normal working vibrations of a fume hood.”

This conclusion is definitive, affirmative, and emphatic. No qualifiers based on the concentration of perchloric acid.

The author’s conclusion: As a manufacturer of perchloric acid fume hoods, Flow Sciences recommends all perchloric acid be used inside a perchloric acid fume hood unless the user of such a hood (and institution) can definitively assure conditions during the procedure afford no risk. Risks are present when perchloric acid is heated or when several types of reactions produce organic peroxides. For these reasons, the author takes strong exception to the 2012 revisions to Z 9.5. We particularly disagree with the omission of this 2003 phrase from the later 2012 document:


“The immediate supervisor and institutional/corporate responsible person (e.g. Safety officer/Chemical Hygiene Officer) always should be notified before these substances are used.”


While the vapor pressure of the perchloric acid at room temperature is not significant in solutions of less than 72%, aerosol electrochemical or digestive reaction products may dry to perchlorate salts or other materials which may collect as a powder inside the fume hood and ductwork. Such deposits may be explosive!

Conversations online regarding whether a perchloric acid hood is really necessary:


These conversations occurred on my Linkedin page during the week of February 11, 2019:


  • Two researchers commented after I aired a video on a functioning perchloric acid fume hood in late January9:
  1. I personally think DUCTLESS FUME HOOD is better. It’s cost efficient, the carbon can also filter poisonous fumes. The filters are actually changed to curb that, and at the same time I am also making my opinion from cost efficiency. I am willing to learn more from an experienced professional though.
  2. Perchloric acid fume hood… Interesting!!! I’m currently using Alkaline fume hood that neutralizes acidic fumes.


Author’s comment: Unless very dilute concentrations of perchloric acid are being used, the author does not recommend the use of ductless activated charcoal filters for perchloric acid procedures. Being a pure carbon source, the charcoal may capture perchloric acid fumes or aerosols and form organic peroxides with the charcoal filter material itself! Such a reaction could be a redox reaction independent of the acidity of the ingested material. We recommend a careful analysis of this possibility before using the technology outlined by both researchers.

  • A researcher needed more clarificationon when perchloric acid hoods are needed and how they should be exhausted.


Hi Robert, Good Day, Perchloric Acid Fume Hood Performance Demo was really good.  We have following doubts and need clarification. Is it necessary to use separate fume hood for perchloric acid applications?   If we are using very minimum qty. of perchloric acid does the fume hood really need wash down systems?


Author’s comment: Whenever perchloric acid use involves very dilute concentrations, the author recommends careful review by Health & Safety before such acid is used in a standard fume hood. Be mindful that lab research or procedures may changeand invalidate any rationale used to avoid perchloric acid fume hood technology.


To the additional concern regarding exhaust exclusivity, most published authorities on this matter believe that the perchloric acid exhaust system should always be kept separate from other chemical exhaust streams.

The British Columbia Ministry of Energy and Minesstates:

”Ductwork for perchloric acid hoods and exhaust systems should take the shortest path to the outside of the building and should not be in the same manifold as other exhaust systems. Horizontal ductwork should be avoided as it creates difficulties for drainage and spray coverage. If unavoidable, horizontal runs should be as short as possible, with no sharp turns or bends, and sloped to ensure drainage.”


The possibility that perchloric acid fume hood exhaust in a mixed exhaust stream could react with fumes and residues from non-perchloric reactions is worth avoiding at all costs. 8

  • A prominent international pharmaceutical company’s Procurement and Environmental Health and Safety officer emailed me the following question: “As you are probably aware ANSI Z9.5 – Laboratory Ventilation, 3.2.5, requires perchloric acid fume hood when handling anhydrous perchloric acid >85%.  Also the requirements under NFPA 45 – 2015: Standard on Fire Protection for Laboratories Using Chemicals, 12.1* Perchloric acid heated above ambient temperatures shall only be used in a chemical fume hood specifically designed for its use…

Does Flow Sciences recommend this fume hood for applications using concentrated perchloric acid (>72%) and/or heating perchloric acid only?   Would you recommend a normal chemical fume hood for use in situations such as preparing dilutions of 4.0ml of 70% Perchloric Acid in 4L of water about once a month?”

This question is entirely justified and arises out of the new language set forth by AIHA Z9.5 already discussed. The officer even copied the newer version of section 3.2.5 into the email inquiry.

Author’s comment: This legitimate question actually turned this white paper into a different and more focused direction! I am grateful the issue was put to me in such an inescapably direct manner.


My answer to this question is therefore also the summary of the entire white paper.

  • I believe ANSI AIHA Z9.5 2012 section 3.2.5 is a step too far in its implied recommendations regarding perchloric acid fume hoods. It is true that the standard requires 85% or greater concentrations of HClOshall always be used in a perchloric acid fume hood. (3.2.5 left column). It is also true that the standard recommends perchloric acid digestions (no concentration mentioned, right column) be conducted in perchloric acid hoods. It is also true that an opened bottle of 70% perchloric acid at 20o C cannot evolve gaseous HClOin quantities capable of reacting with incompatible organic compounds.


No claims are made in the right or left column regarding any other issues involving dilute or concentrated HClO4.

  • So what’s the big deal? The standard is carefully written so that AIHA offers no opinion or recommendation on any other perchloric acid application outside of heating, digestion procedures, or opening a bottle of 70% HClO4 and observing it. Consequently, where is the larger responsibility to designate containment equipment for all remaining reactions? ANSI/AIHA/ASSE Z9.5-2012 currently sets forth no guidance whatsoever on this.


The AIHA Z 9.5 2003 Standard did offer guidance. It was clearly stated in the right column:

“The immediate supervisor and institutional/corporate responsible person (e.g. Safety officer/Chemical Hygiene Officer) always should be notified before these substances are used.”


Even though this “should be” recommendation has not been placed in the 2012 version of 3.2.5, the author believes liability for accidents will inevitably become the legal responsibility of those in charge at involved facilities. As a manufacturer, Flow Sciences continues to believe standard hoods should not become the home for the majority of perchloric acid procedures not now addressed by ANSI AIHA Z9.5 2012. Applications involving perchloric acid should be rigorously examined and past experience heeded before any perchloric procedure is undertaken in a standard chemical fume hood. SOP’s should be agreed to and circulated. Signage should be agreed to and posted. Maintenance should be regular and documented. And most importantly, those supervisors assigned responsibility for such experiments and procedures should monitor and supervise all operations closely.

Anything less puts the administrator and staff at increased physical and legal peril!

One more photographic comment is necessary to summarize this paper. We began by reviewing the uses of perchloric acid. Among these uses, the most prominent is production of ammonium perchlorate, an ingredient in solid rocket fuel. Here are three photos of the PEPCON chemical plant in Henderson Nevada before and after a small fire ignited part of the Ammonium Perchlorate being stored there.

Safety specialists must get the chemistry right in perchloric acid research and production. The perchloric acid fume hood and its use are of primary importance to this mission. Those who manufacture lab safety products, promulgate safety standards, and enforce them must work together toward this goal.

Director of Product and Technology Development

Robert K Haugen  currently designs chemical laboratory containment equipment and develops new relevant technologies for Flow Sciences Inc.in Leland, North Carolina. He has also held positions at Kewaunee Scientific, Jamestown Metal Products, and St. Charles Manufacturing in similar capacities for 31 years. Previously, he did analytical chemical work at the University of Illinois (DNA, wastewater, and crop research) and Lawrence Livermore Labs in California (nuclear weapons research).

Dr. Haugen began his career as a curriculum writer for the Illinois Office of Education, developing texts on energy, urban management, and industrial pollution topics.

He received all his degrees from the University of Illinois in Urbana-Champaign, and is currently a member of the American Society of Heating, Refrigeration, and Air Conditioning Engineers, the American Chemical Society, and the National Fire Protection Association. He has participated in the development of both ASHRAE 110-1995 and the current 2016 update.

Footnotes: (Italics with accompanying footnote indicate a direct quotation from the cited text)

  1. https://en.wikipedia.org/wiki/Organic_peroxide
  2. https://en.wikipedia.org/wiki/Perchloric_acid
  3. http://www.fabricatedplastics.com/case/perchloric-acid-scrubber-system/
  4. Excerpted from twin City Fan and Blower Brochure, 2012, Minneapolis, MN.
  5. Perchloric Acid Fume Hoods, Revision, University of Calgary, 2/7/2003
  6. https://www.drs.illinois.edu/SafetyLibrary/PerchloricAcid
  7. https://en.wikipedia.org/wiki/Perchloric_acid
  8. A Guideline for the Use of Perchloric Acid and Perchloric Acid Fume Hoods, British Columbia Ministry of Energy and Mines, 2016
  9. https://www.linkedin.com/in/robert-haugen-22918546
  10. https://sma.nasa.gov/docs/default-source/safety-messages/safetymessage-2012-11-05-pepconexplosion.pdf?sfvrsn=ceae1ef8_6

Venting Fume Hood Base Cabinets - A Better Way



Frequently, customers have used fume hood exhaust to ventilate hood base cabinets. The author finds both the need for this practice and the designs for them are frequently not well thought-out.

Alternate rationales and approaches to this ventilation method are reviewed with clear-cut recommendations.

The Historical Rationale for Cabinet Ventilation:


An acid cabinet contains jugs of concentrated acid which can give off fumes if improperly stored with loose caps or drying spills on the jug exterior. Solvent cabinets store solvents which could contribute to a lab fire if internal solvent fumes caught fire. For years, lab designers have assumed these issues could be addressed by gently pulling air through these cabinets and into the fume hood. No fumes; no danger. It’s as simple as that!


The Realities of Specified cabinet ventilation:


Reflecting this concern, cabinet vents have been called out in construction specifications for laboratory chemical fume hoods with base cabinets. Here is an example of a construction specification for a cabinet vent for flammable (solvent storage) cabinets:


“Chemical hoods shall have ventilated base cabinets that comply with NFPA 30, with a built-in partition for separation of incompatible chemicals. Except in ADA hoods, the cabinet shall be able to hold four liter sized bottles on both the top and bottom shelves. 1


However, NFPA 30 says the following about vented fume hood cabinets containing flammables 2:


9.5.4* Storage cabinets shall not be required by this code to be ventilated for fire protection purposes. If a storage cabinet is not ventilated, the vent openings shall be sealed with the bungs supplied with the cabinet or with bungs specified by the cabinet manufacturer.* If a storage cabinet is ventilated for any reason, the vent openings shall be ducted directly to a safe location outdoors or to a treatment device designed to control volatile organic compounds (VOCs) and ignitable vapors in such a manner that will not compromise the specified performance of the cabinet and in a manner that is acceptable to the authority having jurisdiction.


The need for venting corrosive (acid) storage cabinets is also defined by some institutions. The University of Wisconsin sets forth the following: 3


Optional chemical storage cabinets: For those fume hoods provided with VENTED under counter chemical storage cabinets to reduce odor, each cabinet shall be connected to a 1.5-inch diameter vent tube which penetrates and is sealed to the fume hood countertop. The tube shall also be sealed to the chemical storage cabinet in the rear side wall and terminate behind the fume hood baffle.5


One may note the lack of detail in this description. Critical data such as cabinet exhaust rate is completely ignored. 4


With the lack of such specificity, lab equipment providers have been left with a default definition of a vent tube running from the cabinet through the work top into hood baffle area. An illustration of the approach is shown below 5:

Two comments need to be made here regarding these illustrated approaches:

1 – Neither acid cabinets nor solvent storage cabinets use this approach consistently. In the field, such cabinets frequently have no ventilation system whatsoever!


The author attempted to find some photographic evidence online that vents from cabinets into fume hoods were still being used; I found limited photographic examples.  Below, note examples I did find:

Clearly, this default approach is not universally used.

2 – Justification for such a venting procedure is questionable.

Let’s take each cabinet type separately and examine the problems with venting it using a tube into the fume hood rear:

  1. Acid cabinet venting:
  • How much air will go through such a cabinet using the vent system with specifications, as described previously?


The cross section of this pipe is (pi)r2=0.752 X 3.14 = 1.76 sq. in = 0.0122 sq. ft.

At a hood face velocity of 100 fpm, CFM = V*A = 100 * 0.0122 = 1.12 CFM

A 36” base cabinet has an internal area of 22” X 34” X 36” =26,928 Sq. inches, or     15.6 cubic feet. This leads us to have a cabinet with 1.12/15.6 = 0.07 air changes per minute (ACM); or 4.3 Air Changes per hour. When the door of the cabinet is opened, it would have a face velocity of 1.12 CFM/8.5 sq. feet = 0.13 FPM. Hardly capable of containing any fumes!

  • Is there any way to stop the escape of these fumes without the vent? We have just shown this type of vent is barely effective with venting fumes from cabinet acid spills and incapable of preventing fumes from escaping if the cabinet door is opened! There is little rationale for using such a vent system which attempts to piggyback cabinet ventilation of the fume hood exhaust.

More robust ventilation may be achieved by venting such a cabinet through the baffle area at the hood top. In this region of the baffle, there is a larger negative static pressure and therefore more “draw” on the base cabinet vent port. A schematic of such a system is shown below:

One can also use shelf liners inside the cabinet made from inexpensive cement board which is primarily limestone Ca(OH)2, a base. Such a sacrificial panel can neutralize (ionize) small drips of acid, and reduce fumes. All Flow Sciences acid cabinets come with this feature as standard.


Additionally, it is highly recommended that standard operating procedures (SOP’s) include steps mandating the cleaning of liquid acid off of glass containers and firmly closing each cap (ensuring a sufficiently tight seal) before returning the containers to the acid cabinet.



  1. Solvent Cabinet Venting:
  • The “flow” through the cabinet with a 1.5” vent does not facilitate a sufficient volumetric flow rate to remove spilled solvent vapors from the cabinet. See [1. a) 1)]


  • Solvent cabinet doors, unlike acid cabinet doors, have no vent holes. As noted above, the double-walled cabinet is supposed to keep heat out to prevent cabinets from allowing their contents to burn in a general lab fire. As a practical matter, these cabinets are virtually air-tight when closed. This means that the 1 CFM throughput calculated with the louvered acid cabinet would be even lower with the non-louvered solvent cabinet.


In the defense of NFPA, the association included in NFPA 30 the required way to vent a solvent cabinet, and it is not with a vent kit through the work top. See below 8:

Figure 2: NFPA recommended solvent cabinet ventilation technique


While this method assures more robust ventilation, it increases airflow through the cabinet, which will increase the amount of heated air running through the cabinet in a combustion area.


Keep in mind, a solvent cabinet is designed to keep heat out during a lab fire.6 It is UL 1275 tested with a heated oven that elevates external cabinet temperature to ~1300OF over 10 minutes while cabinet internals must stay under 350oF. This test is purposely run with NO ventilation through sealed bung holes! 7

Imagine repeating this test with an actively ventilated solvent cabinet. Now air being passed through the cabinet from a burning environment at a severely elevated temperature would elevate the temperature of the cabinet interior.  In this case, higher levels of cabinet exhaust will draw more fire-heated air into the solvent cabinet. This is definitely at cross-purposes with the cabinet’s design intent!


This entire analysis is also summarized in many catalogs, including Grainger, who point out:

Don’t Vent Unless You Have To

 “While cabinet manufacturers may provide the bungs for ventilation purposes, venting flammable liquid storage cabinets is NOT required or even recommended by any federal regulatory agency. Cabinet manufacturers include venting bungs for users who may be required to vent by state or local codes, individual company policies, insurance carrier policies or any other authority having jurisdiction (AHJ).”


So, is there any way to stop the escape of solvent fumes without the vent? There really is not, particularly when NFPA does not require venting and mandates elective vents use an independent fan as shown in figure 2. Again, SOP’s in various facilities may recommend different things. But always use approved solvent containers. and clean up spills to prevent fire-friendly conditions in the lab!



  1. Do not ever use a through-the-top vent system and expect the safety of an acid cabinet to be improved. If local standards require this venting procedure, do your best to design countermeasures to neutralize the added risk.


Always use sacrificial shelf liners that neutralize acid. Enforce SOP’s that require closing acid bottles tightly. Consider one of the more robust method of ventilating the cabinet discussed in this paper.


  1. Do not ever use a through-the-top vent system and expect the safety of a solvent cabinet to be improved. Venting in this manner is an arguably futile containment strategy based on the low airflow through such a vent.


If local standards require a venting procedure, follow NFPA recommendations as set forth in NFPA 30, and do your best to design countermeasures to neutralize the added risk.


It is likely fire authorities will prefer the separate remote fan method outlined above that is advocated by NFPA 30. In addition, enforce SOP’s that require special solvent canisters with spring closures, and clean up spills inside the cabinet immediately!

3. One final note regarding the fume hoods in all of the above examples. A separate question exists about whether such fume hoods should be left running or turned off during a fire. You can imagine this question is even more complex and significant than base cabinet ventilation.We will discuss this issue in an upcoming White Paper.

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  1. Laboratory safety Design Guidelines, University of Medicine and Dentistry of New Jersey, 1/3/2007
  2. NFPA 30, 2012 Edition, p 30-28
  3. University of Wisconsin Department of Environment6al Health and Safety, Acid Cabinet Specification, (Un Dated), https://ehrs.upenn.edu/health-safety/lab-safety/lab-design-equipment/acid-cabinet-specification
  4. SEFA, as of 2017, does not set forth anything more than a discussion about where cabinet may be justified, without ever stating the mechanism for how it is to be achieved.
  5. Thermo Scientific Hamilton Air Flow Products, 2010, p.105, 106
  6. The 10-minute time limit limit iwas decided as time enough in a fire to evacuate personnel and to allow sprinklers to activate. file:///C:/Users/drbob.FSIDOMAIN/Desktop/TT-Safety-Cabinet-Performance.pdf
  7. The time temperature curve as defined by ASTM E119, UL 263 and NFPA 251 are virtually all the same: The curve starts at 68°F (20°C) at 0 minutes, continues to 1000°F (537°C) at 5 minutes, and for safety cabinets finishes at 1300°F(704°C) at 10 minutes as measured on the outside above the flame. The actual flame touching the cabinet can measure ≈1600°F (871°C)., file:///C:/Users/drbob.FSIDOMAIN/Desktop/TT-Safety-Cabinet-Performance.pdf
  8. Flammable Liquids Storage Cabinets, Part 2 of 2, Bob Benedetti, Principal Engineer, Flammable Liquids, NFPA. Campus Fire Safety eNews Zone, p8, 2011

Director of Product and Technology Development

Robert K Haugen  currently designs chemical laboratory containment equipment and develops new relevant technologies for Flow Sciences Inc.in Leland, North Carolina. He has also held positions at Kewaunee Scientific, Jamestown Metal Products, and St. Charles Manufacturing in similar capacities for 31 years. Previously, he did analytical chemical work at the University of Illinois (DNA, wastewater, and crop research) and Lawrence Livermore Labs in California (nuclear weapons research).

Dr. Haugen began his career as a curriculum writer for the Illinois Office of Education, developing texts on energy, urban management, and industrial pollution topics.

He received all his degrees from the University of Illinois in Urbana-Champaign, and is currently a member of the American Society of Heating, Refrigeration, and Air Conditioning Engineers, the American Chemical Society, and the National Fire Protection Association. He has participated in the development of both ASHRAE 110-1995 and the current 2016 update.

Fume Hood Fires…Smoke, Heat, and (Finally) Illumination!


  1. A fire breaks out in your fume hood.
  2. What do you do?
  3. Should you put it out? Should you run? Should you turn off the hood fan?
  4. Should you activate the building fire alarm?
  5. Wait a minute! Are YOU on fire????

Very little exists in one place to answer these questions. Policies actually differ. Accountabilities are sometimes unclear. This White Paper examines all these issues in as clear and direct way as possible. One thing is clear: these questions need to be thoughtfully addressed before the fire starts!

The Historical Perspective:


UCLA had a tragic safety episode in 2008. A fume hood lab fire killed Sheri Sanji, a research assistant. Any lab safety incident, including a fire, is likely preventable. Fire is a very publically visible symptom of poor lab safety. It is up to those engaging in research to assume front-line responsibility for their own safety. Fire is one kind of accident that occurs in fume hoods; many other misadventures are also possible inside such a containment area.

Michael Wrightcorrectly analyzes the proper safety perspective for such tragedies: “Our own (safety) investigations are about causation and prevention, not guilt. We believe in accountability, and we support civil and criminal penalties where they are appropriate – as I would argue they are here (UCLA). But that’s not our goal. The real issue is how we prevent such tragedies in the future. And from what I have seen, academic labs have a ways (sic.) to go. I don’t know any industrial lab director who would claim that he or she is not responsible for safety. PI’s (Principal Investigators) are equally responsible.  We won’t make progress where they don’t acknowledge it.”

Unfortunately, many laboratories are not organized effectively to collect safety data, let alone improve adverse conditions.

Chemical fume hoods found in high school, junior college, and college chemistry labs are found to have many more accidents than hoods in commercial labs.2

One study by Dow, DuPont, and Corning cites an OSHA report concluding a college researcher is eleven times more likely to be hurt than a researcher in a commercial lab. Reasons pertain to cultural differences between how educational and commercial labs operate, safety priorities taking second place behind academic research goals, and countermeasures only being considered after something goes wrong.

John K. Borchardt confirms the differences between academic and commercial lab settings and their respective safety records on lab fires and accidents in 2013: 3

“Industrial and government labs generally have good safety records based on personnel training, safety inspections, and maintenance of equipment. However, the frequency of academic research laboratory accidents is more than ten times that in industrial labs.”

Chart 1 shows the types of lab accident incidents reported and the frequency of their occurrence. Explosions and thermal burns were the second most frequent type of incident, encompassing injuries caused by exposure to extreme heat such as from a burner or hot water.

Chart 2 shows the types of injuries resulting from these lab incidents. Burns and lacerations together accounted more than one-half of all reported injuries.

The dominant percentage of burns and lacerations in lab accidents are significant. Burns and lacerations are typical in fume hood fires. We can anecdotally fathom this situation from the ten examples cited in the chart below:

Ten Fume Hood Fires and Explosion Examples Located by Google:

#DateLocationCasueltiesCauseRemedies in FutureWeb Address
112/28/2008UCLA1 DeadImproper Procedure, lack of Protective clothing, Uninformed AssistantsDrills, more visible equipment, train personnelhttps://en.wikipedia.org/wiki/Sheri_Sangji_case
21/7/2010Texas Tec.1 Serious injuryMaking too much chemical, PI uninformed of SOP, removed explosive compound from hood to grind, BOOMUse SOP, wear lab coat, wear gloves & lab coat & eye protectionhttps://www.depts.ttu.edu/research/integrity/CSB-response/downloads/TTU_EHS_accident_report.pdf
310/27/2011Texas Tech0 InjuriesExplosion of acid waste storage bottles stored under fume hoodDo not allow acids and organic solvents to be mixed in same bottleshttp://today.ttu.edu/posts/2011/10/statement-concerning-second-laboratory-accident
411/13/2015UC Berkeley1 InjuryExplosion of a drypowder while being scraped from filter per SOPFollow SOP and scrape while wet. Wear protective gear and double-glove, fix SOP.https://ehs.berkeley.edu/lesson-learned-dry-scraping-causes-chemical-explosion
53/16/2016U Hawaii, Manoa1 injury, arm amputationPost Doc Investigator ignited 49 L tank with explosive gas mixture of

O2, CO, and H2 with spark

15 safety violations & $115K fine. See the article for details!

Virtually all SOP’s ignored

6Spring 1997U Kentucky1 student minor injuryhalogenated organicsolvents were involved, but the exact cause may never be known.Do not mix solvent and nitric acid (see footnote 5)http://www.ilpi.com/safety/explosion.html


79/29/2011U of Maryland2 Students 1st and 2nddegree burnsWaste acids mistakenly added to an organic reagent bottle.Do not re-purpose reagent bottles as waste containers. Upgrade SOP. Have instructor review before experiment.http://cenblog.org/the-safety-zone/2011/09/explosion-at-the-university-of-maryland/


84/26/07U Cal Irvine1 student, first degree burn and cut as he raised FH sashExplosion of diethyl ether and toluene derivatives on a hot plate.Tolunesulfonochloride SOP needed improvement. Temperature too high on hotplate.

Find alternate for diethyl ether.



93/2012Texas Tech U0 InjuriesSulfur-Metal reaction in waste bin on floor outside fume hoodProperly segregate waste materials. Improve SOP’s. Consult with EH&Shttps://www.depts.ttu.edu/research/integrity/lessons-learned/march-2012.php
106/24/14Oak Ridge Nat. Lab0 Injuries; 6 evacuatedSpontaneous hotplate activation ignited a fire in hood while unattended. Another possibility is postulated below using a photograph of the incident in questionUnplug equipment when not in use.https://opexshare.doe.gov/lesson.cfm/2014/6/24/4332/Deflagration-and-Fire-from-Malfunctioning-Lab-StirrerHot-plate/?responsive=false


This information can be summarized as follows:

1. Fume hood fires are a significant problem mostly found in institutions of higher learning and academic research.

2. Based on post-accident analysis, reasons for accidents include:

  • Little or no training of lab personnel on operating critical research and safety equipment
  • Little knowledge of the properties of the chemicals involved
  • Poorly formulated or non-existent SOP’s
  • No peer (or supervisor) review of proposed procedures
  • Little knowledge of required yields or separation procedures
  • Poor or non-existent in-lab supervision of the student/researcher
  • Poor monitoring and disposal of lab waste
  • Poor lab attendance record-keeping which blurs accountability
  • Failure to keep reacting materials inside the fume hood containment area
  • Failure to properly remove discarded chemical waste from the fume hood or underlying base cabinets
  • Failure to institute safety procedure changes after any given accident. Three of the ten accidents in the chart above all were similar and all occurred at the same institution within three calendar years.

3. Finally, we need to step back from any procedure before it is done and ask four questions:

  • What, exactly, are we doing?
  • How are we doing it? Can experiment be done in a short period, or will several staged sessions be required?
  • What could go wrong?
  • Where are safety resources?
    • Extinguishers; which should be regularly inspected and assigned to the work area accordingly by fire class (e.g. A, B, C, D, etc.)
    • Fire Blanket
    • Drench shower
    • Fire alarm
    • Master power switch and gas shut-off
    • The exit; should always remain unlocked and accessible


Going back to the questions posed in the abstract, none can be answered without having a safety plan similar to the one outlined above. 4

Answers to Abstract questions:


What do you do? Should you put it out? These questions are addressed in the bulleted list from the previous section. If a clear list of materials and an understandable procedure have been established, many difficulties will have already been defined and anticipated, including whether extinguishing the fire itself is a good idea.

Should you run? You should probably walk to some or all of the items in the list, depending on contingencies already considered in the planning stage of the experiment.

Should you turn off the hood fan? Fire and facility ducting practices in different areas of the USA affect the answer to this question. Some areas require hood exhaust fans be automatically disabled if duct smoke or heat is detected. In many other places, local codes require ducts be heat-isolated and fans remain operating during smoke and heat detection. Checking with mechanical personnel at your facility will help determine procedures to be used in a given facility.

Should you activate the building fire alarm? Know fire alarm activation policies, but in cases of an active fire in a lab, the answer to this question will most often be yes.

Wait a minute! Are YOU on fire???? Here, we really need to step backward a bit, ANY experiment with fire dangers present, should never be done solo. Using a fire blanket or other personal protection usually requires two people to be effectively carried out. The one death outlined above occurred with other individuals in the same lab working on other projects (e.g. UCLA, line one on table above). These individuals were not informed about the nature of the disaster-destined procedure and predictably participated ineffectively in the emergency.


  1. Michael Wright, Director SHE, United Steelworkers 10/5/2018, American Chemical Society CHAS web conference
  2. Jon Rvans, Royal Society of Chemistry, Safety First?, 2014, https://www.chemistryworld.com/features/safety-first/7413.article
  3. Running Your Labs Like a Business, John Borchardt, 2008, Lab Manager Magazine, https://www.labmanager.com/business-management/2008/07/running-your-lab-like-a-business#.XBkYj1xKiM9
  4. SUPPLIMENTAL: EduRiskTM provides education-specific risk management resources to colleges and schools, and is a benefit of membership with United Educators (UE) Insurance, 2014, https://edurisksolutions.org/WorkArea/DownloasAsset.aspx?id=1894…135


  1. University of Kentucky Fire (Chart, Item 6)

Director of Product and Technology Development

Robert K Haugen  currently designs chemical laboratory containment equipment and develops new relevant technologies for Flow Sciences Inc.in Leland, North Carolina. He has also held positions at Kewaunee Scientific, Jamestown Metal Products, and St. Charles Manufacturing in similar capacities for 31 years. Previously, he did analytical chemical work at the University of Illinois (DNA, wastewater, and crop research) and Lawrence Livermore Labs in California (nuclear weapons research).

Dr. Haugen began his career as a curriculum writer for the Illinois Office of Education, developing texts on energy, urban management, and industrial pollution topics.

He received all his degrees from the University of Illinois in Urbana-Champaign, and is currently a member of the American Society of Heating, Refrigeration, and Air Conditioning Engineers, the American Chemical Society, and the National Fire Protection Association. He has participated in the development of both ASHRAE 110-1995 and the current 2016 update.

Scale-Up Chemical Syntheses and Larger Fume Hoods: How History Inspires Present Realities


For years, there has been a demand for large fume hoods and other containment devices to handle bulky process equipment. Many types of experiments are placed in these hoods: syntheses involving distillation columns, reflux reactor flasks, and racks of analytical vessels like Kjeldahl digestion flasks.


This paper reviews the types of large fume hoods now available, typically desired units, applications such fume hoods are used for, and the changes and improvements made in these units in the past three decades.

Typical Large Fume Hoods


Years ago, standard floor-mount fume hoods were called walk-in hoods. Nobody should walk into/work inside these units, but equipment on carts would frequently be pushed into these units for manipulation.

One major difference between bench hoods and floor-mount hoods is sash and exhaust requirements. Floor mount hoods are sized at 50% open. This means the desired face velocity (80 FPM, for example) is calculated with the bottom vertical sash closed.The primary reason for this restricted opening is to avoid the extraordinary amount of air that would be required to have a floor-to-roof opening running at an acceptable face velocity. Since exhaust air HVAC expenses can be higher than $10/CFM-year, most users are averse to running these hoods with the sash fully open.

The Floor-Mount/Bench-Top Hybrid:

Frequently, a fume hood “halfway” between a bench hood and a floor-mount is the best choice. This fume hood may be used with tall distillation or chromatography columns, or with bulky equipment which never needs to be wheeled anywhere. This hood is frequently called a distillation fume hood orhigh-boy.

Present Realities:

Obviously, floor mount hoods are far less frequent in modern labs than bench hoods. When one is purchased, there is a high likelihood there is a specific purposefor the device. In other words, such a hood needs to be closely evaluated before it is sized and constructed. As stated in a recent published paper *3*, applications should always help define the containment device.

This general principle has a specific effect on floor-mount and distillation fume hoods. They are often defined by the sizeof the equipment inside. Examples for floor-mount fume hoods follow:

     1. Dimensions (particularly height and depth)

    2. Additional Features (special spill protection, grounding strips, etc.)

     3. The need to verify containment of all unique aspects using ASHRAE 110

     4. Custom installation instructions where required to adapt hood to known access passageways (see below):


  • Large floor-mount fume hoods have a long history in laboratories. They are built larger to accommodate large lab equipment or processes and come in a variety of sizes and accessories.


  • Unlike more conventional bench fume hoods, these hoods will normally be customized to accommodate specialized experiments or procedures. It is highly recommended that such fume containment devices be customized to fit the intended application.


  • The ideal floor-mount fume hood must always:


  1. Be built to fit the application
  2. Be containment-tested, preferably while performing its intended function.
  3. Be sold with a manual that focuses on its specific purpose, use, assembly, and maintenance specifications.


  1. Primary Containment for Biohazards: Selection, Installation and Use of Biological Safety Cabinets, 3rdEdition, September, 2007, p. 6
  2. https://flowsciences.com/performance/
  3. Necessity is the Mother of Innovation, Haugen https://flowsciences.com/necessity-is-the-mother-of-innovation/


Director of Product and Technology Development

Robert K Haugen  currently designs chemical laboratory containment equipment and develops new relevant technologies for Flow Sciences Inc.in Leland, North Carolina. He has also held positions at Kewaunee Scientific, Jamestown Metal Products, and St. Charles Manufacturing in similar capacities for 31 years. Previously, he did analytical chemical work at the University of Illinois (DNA, wastewater, and crop research) and Lawrence Livermore Labs in California (nuclear weapons research).

Dr. Haugen began his career as a curriculum writer for the Illinois Office of Education, developing texts on energy, urban management, and industrial pollution topics.

He received all his degrees from the University of Illinois in Urbana-Champaign, and is currently a member of the American Society of Heating, Refrigeration, and Air Conditioning Engineers, the American Chemical Society, and the National Fire Protection Association. He has participated in the development of both ASHRAE 110-1995 and the current 2016 update.

Shipping, Assembling, and Installing Bulky Exhaust Equipment in a Lab Facility




Dr. Bob Haugen,

Flow Sciences; 10/22/2018


Many people who design labs or work in them may have little idea of how hard it is to get large equipment set up and working in a modern lab environment!


The trades responsible for these feats are often not appreciated for what they do. This paper will review ways to minimize installation issues (expenses) before products are deliveredusing many of the same steps discussed in previously published papers1:


Even though delivering, unloading, staging, distributing, and assembling are required steps in all lab construction,there are design aspects of lab equipment that can contributeto its successful field installation.



While this whole delivery issue is separate from the manufacturing phase of heavy lab equipment, a product cannot become useful until it travels from the on-site delivery trailer to the actual lab areain the facility where it is to be installed.


I have seen cases where a matter of inches prevented a product from making a hallway turn or being loaded into an elevator. If no advance planning has been undertaken, local contractors are often forced to either partly disassemble the equipment or temporarily disassemble the building itself. These adventures can be costly if necessary arrangements have not been anticipated.


Flow Sciences and other lab equipment manufacturers have actually taken steps in product design to minimize the kind of distribution difficulty outlined above.


Flow Sciences fume hoods, base cabinets, and plumbing components are modularized in design so various sub-parts are easy to separate and move to the installation site independently when the whole unit cannot make it in one piece.

Below is an actual field example. This large multi-sashed unit was disassembled for carrying to the user’s laboratory in the lab elevator and then re-assembled.

In another case, a floor-mount fume hood was divided into three separate pallets of materials to avoid disrupting hallway traffic and tight corners at a working lab. Not only did this step allow installers to identify components, the manual gave easy-to-follow re-assembly steps reviewed in the next section!


Documenting this procedure is typically covered in the owner/operator manual. Because we now all operate in the age of electronic media, FSI can modify or expand a standard manualto include assembly/disassembly instructions based on customer input. Our inside sales team was alerted by the customer receiving this floor mount fume hood that the path to the target lab included sharp corners and low ceilings. See below special assembly pages included in this floor-mount fume hood manual.


Flow Sciences and other equipment manufacturers have moved toward flexible plumbing within the fume hood itself 2, 3, 4because such fittings and plumbing eliminate hard plumbing with fragile sweat solder joints which can break free during transit. Plumbing is also easily attached to threaded connectors already installed by the building plumber. Again, this option is outlined in the manual.

Electrical devices provided with the product are Pre-Wired in all cases to a junction box. Schematics and wiring diagrams are in the installation manual.

Miscellaneous information on safe fume hood use, velocity alarms, cabinets are all in their respective manuals included with shipment.


Errors may not occur ifthere is clear and comprehensive communication between the manufacturer and lab customer! Fine laboratory equipment is out there, but knowing where it comes into the buildingand where it must gomust be clearly understood by all parties in the manufacturing/installation process. Large equipment is, well, LARGE.


It may need to go up elevators, through narrow hallways, and into labs through narrow doors. In many cases this requires partial disassembly, distribution, and reassembly at the installation location. These challenges may exist in both new construction and inevitablyin operating labs requiring new equipment.


In spite of these challenges, the modular design technologies of newer lab equipment and more flexible electronic literature and communication formats offer hope for large exhaust equipment to be installed quickly with few problems.


Other issues with new, large equipment include incorporating new exhaust systems into building air balance, adjusting heating and cooling loads for thermostatic control, and making certain additional duct runs are incorporated into the building structure.



Director of Product and Technology Development

Robert K Haugen  currently designs chemical laboratory containment equipment and develops new relevant technologies for Flow Sciences Inc.in Leland, North Carolina. He has also held positions at Kewaunee Scientific, Jamestown Metal Products, and St. Charles Manufacturing in similar capacities for 31 years. Previously, he did analytical chemical work at the University of Illinois (DNA, wastewater, and crop research) and Lawrence Livermore Labs in California (nuclear weapons research).

Dr. Haugen began his career as a curriculum writer for the Illinois Office of Education, developing texts on energy, urban management, and industrial pollution topics.

He received all his degrees from the University of Illinois in Urbana-Champaign, and is currently a member of the American Society of Heating, Refrigeration, and Air Conditioning Engineers, the American Chemical Society, and the National Fire Protection Association. He has participated in the development of both ASHRAE 110-1995 and the current 2016 update.

Necessity is the Mother of Innovation


Generally speaking, scientific equipment manufacturing companies that correctly perceive and then meet research customer needs will succeed. Researcher-manufacturer cooperation is vital to such success. The two entities must have a real conversation about what the researcher uses as a process and how current containment is either ineffective or not present. The designer-manufacturer then makes recommendations and proposes a solution. In many cases this proposed solution must be far more than a quotation. It must also include enough information to let the customer visualize how this product will facilitate the researcher’s application.

Problem-solvers must be involved on both sides of the interaction!

This paper cites four examples of problems Flow Sciences was able to address with a variety of standard products with unique modifications. In each case, the mutual success of our customer and Flow Sciences was achieved.

Case 1: The fume hood with a nearly invisible work area.

A research company had a basement laboratory with a custom fume hood designed to handle several volatile and corrosive organic chemicals. The equipment was older, and it was also very difficult to use because of its poorly illuminated interior and small viewing window eclipsed with glove ports.

Because this customer was overseas, a large amount of email communication was involved in answering the following questions, all of which need attention for any custom application fume hood:

1) What was purpose of the device and the processes conducted in it?

2) What are the dimensions of the current unit?

3) What chemicals are used in the device?

4) What voltages and phases of electricity are used inside this device?

5) Are explosion-proof fittings required?

6) Who is our contact person to approve final drawings?

7) Are there shipping requirements or preferences?

On similar work for any containment device manufacturer, a lengthy number of emails or phone calls is typical, particularly if you involve contractual issues such as price, delivery, and scope. What is not typical is to get into application issues as thoroughly as Flow Sciences does in its communication.

From an email exchange that exceeded 50 messages and responses, Flow Sciences determined that a modified standard fume hood could handle the customer’s application with augmented visibility, containment, and value. We were able to get approval drawings agreed to and begin manufacture shortly after our questions (and theirs) were answered. See the photos below:

The original unit was stainless steel with two glove ports through a fixed window. The gloves in the fixed glass panel consumed most of the existing glass area allocated to viewing the workspace. A hinged outward-swinging access door on the original unit was awkward to use and increased containment issues as well.

The new unit was constructed from a combination vertical/horizontal sash Saf-T Flow fume hood with two panels. One panel housing the gloves was fixed in the sash frame, the other was a narrow sliding glass panel only 17” in width.  The entire sash could be unlocked and raised vertically for cleaning and set-ups, however the hood was designed to ventilate with only the 17” wide horizontal sash available for adding samples to the hood. This sliding element caused no loss of containment when the door was opened and closed during ASHRAE 110 testsdone at the Flow Sciences facility in Leland, North Carolina. Additionally, the custom 5’ unit was energy efficient, requiring an exhaust volume of only 233 CFM with no detectable containment loss under a variety of additional test conditions!

Case 2: The hood that suffered containment loss when heated procedures were used inside:

Many times, we are confronted with customers who find their current fume hood unable to accommodate high-temperature reactions when the sash is closed under VAV (variable air volume) operating conditions. When high temperature, VAV, and a unique procedure are all involved, Flow Sciences always asks our customer about the chemicals & procedures used and then uses the ASHRAE 110 test procedures to test containment using this process. These “seven questions” were reviewing above in case 1.

In the case depicted in Fig. 3, containment of the hood was evaluated in using the ASHRAE 110-2016 test methodwith a modified location and temperature of the diffuser. These tests were witnessed by the customer.

The hood passed all tests (figs. 4 & 5) with no detectable tracer gas leaving the containment area.

Case 3: Waste removal from animal cages.

Animal waste isolation and removal is a concern in virtually all research animal applications.

Again, we got answers to all seven questions already discussed in Case 1 from the customer. The review of these answers revealed two unique aspects of this application:

  • The need to insert and remove cages from the work area (A large vertical opening was therefore provided.)
  • The need for a mechanism for isolation and removal of the waste. We recently provided such a unit that is shown below which contained well under various tests: (Note the wide funnel port and wheeled-in carrier container below.)

This fume hood met the process criteria of the customer and provided an easy way to isolate the waste and dispose of it while minimizing waste contamination issues. The stainless steel interior allows simplified cleaning regimens with strong disinfectants.

The customer received documentation of great ASHRAE 1101, Human as Mannequin2, and low face velocity containment results for this unit. This hood became one more tested and proven solution for animal cage cleaning Flow Sciences can offer customers!

Case 4: Hazardous chemicals requiring interconnecting hoods with pass-through features

This particular fume hood almost appeared to be an exception to “listening to a customer” because it started with Flow Sciences receiving a detailed, written specification and limited ability to discuss the specification with the customer. The conditions of the quotation specified this condition.

We were able, however, to answer many of the seven questions by “asking” the specification.

We knew, for instance, the fume hood dimensions (question 2). We knew this particular fume hood array was to be used to analyze several caustic substances never to be removed from the hoods during analysis (question 1).Electrical outlets and voltages were called out (questions 4 & 5). We were also told in the specification which services were to be provided and where they were to be placed (indirectly, question 1). We were even given a paint vendor to use and which color was to be provided (again, a strong question 1 indicator). The construction contact was listed in the specification (questions 6 & 7).

While not ideal, this way of quoting and eventually testing a containment device represents a scenario which is encountered frequently.  There are three things which the manufacturer can do when direct customer contact is not possible:

  1. When no humans are present, “ask” the specification! Any relevant specification detail should be used to justify the eventual product design.
  2. Be certain a detailed sign-off drawing is approved before unit construction begins.
  3. Test, test, test! Assume containment is critical and include standard containment tests plus movement of hood internals and manipulative tests such as the Human-As-Mannequin (HAM) test.

ASHRAE 110 and the HAM containment tests were run with excellent results. (Figs. 11-13)

There are obvious shortcomings when manufacturers and customers do not or cannot directly talk to each other. The manufactured product will reflect an anticipated, rather than a spoken need. Changes from original research intent to what is needed at the time of purchase order approval are not possible. Back-charges, change orders, and delays during the installation process all become more likely. In spite of these things, some positive results can still be achieved largely based on the ability of the specification to “answer” key questions.


This white paper began with a discussion about how communication is necessary for complex containment solutions to be reached between a research entity and an equipment manufacturer.  The first three examples in this paper show effectively how such containment challenges rarely involve a catalog of equipment or a pre-written job specification. The last example demonstrates how success can still be achieved if the specification is used as a basis of assessing product requirements.

Still, the best guarantor of success is direct communication. People must talk to each other about specific applications and containment requirements. Once such a conversation has occurred, a substantive containment approach may be confidently agreed upon. Such an agreement must include enough information to let the customer visualize how this product will facilitate the application.

Problem-solvers clearly must be involved on both sides of such an interaction! Several key steps must take place before any complex containment issue can be sorted:

1) The customer’s application must be stated by the customer and acknowledged by the manufacturer.

2) A modified containment device must then be proposed.

3) This device must be constructed based on sign-off drawings approved by the customer. This device must be shown to work with the application using recognized test procedures which sometimes may require modification.

If all of the above goes well, both the customer and the manufacturer benefit!


  1. ASHRAE 110-2016 – Methods of Testing Performance of Laboratory Fume Hoods, American Society of Heating, Refrigeration, and Air-Conditioning Engineers, 2016.
  2. Side-by-Side Fume Hood Test Using ASHRAE 110 and “Human as Mannequin” to Compare Performance of a Jamestown Conventional Fume Hood and a LBNL High Performance Hood, Lawrence Berkeley National Laboratory, California Energy Commission; March 21, 2005.


Contact Flow Sciences


Common Fume Hood Containment Problems


For many years, the containment/lab exhaust industry has frequently heard the phrase “my fume hood doesn’t work!”

Most of us who start our careers being frustrated with this comment eventually learn that it is a cry for help from people who want effective exhaust and are focused on the most tangible element of the exhaust system, the exhaust hood. Technically, the customer is 100 percent correct. If fumes escape from the containment area, the hood is not working. We only need to add two words to make the sentence both technically and comprehensively correct: “the fume exhaust system is not working!”

While there are “bad” fume hoods 1, anything wrong with the entire system (exhaust fan, ductwork, building configuration, make-up air, automated regulative dampers) may cause a lack of containment in a hood. As fume hood manufacturers, we strive to make our hoods robust; that is capable of surmounting minor issues in other lab exhaust system components. However, major system issues 2 will always be a threat to system containment.

The situations described below involve fumes being detected in labs. This scenario is frequently discovered or verified with the ASHRAE 110 containment test. A complete description of this test is beyond the scope of this paper, but it can be summarized as diffusing a tracer gas, usually sulfur hexafluoride (SF6), into a fume hood. A sensor is placed in the breathing zone of a mannequin 3” past the hood sash plane. If SF6 is detected in the mannequin breathing zone at a concentration at or above 0.050 ppm, the tester and colleagues start looking for things that may be adversely affecting fume hood containment.

1. Some early hood designs would release contained fumes because fumes would get trapped between sash glass and bypass when the sash was raised. This is just one of many examples.  

2. Duct leaks, debris in ductwork, broken fan belt, and stuck VAV dampers are some examples.


This paper will look at six “case studies” chosen from a lifetime of lab experiences. From these examples, I will suggest a procedure for “fixing” field problems with containment that frequently occur. Each case study is a specific example of the corresponding category on the chart which follows the six examples.

1. Exhaust Fan will not operate.

Once, during a vacation break at a university, I was attempting to field test fume hoods for containment but could not turn the units on. The hoods had no individual “on-off” switches. I was left trying to stare at yet-to-be labeled circuit breakers, one or more of which activated the hoods. I finally discovered the fans were “three phase” units requiring electric three-point relays connect all three hot leads to the fan at once. Once these relay switches were found and made operable, the fans started. This experience taught me that anyone assigned to test construction site exhaust systems in the field should pre-arrange to have a building superintendent present to get things running. It is no fun to have to return to a jobsite a second day because nobody familiar with the system was there to turn the complex exhaust system on during the first visit!

2. Unexpected corrosion in a fume hood producing no other telltale symptoms.

Many years ago, an oil exploration firm was beginning research work in a new lab complete with new hoods. It was the very first VAV (variable air volume) set-up I had ever seen. Although the lab was full of fume hoods, it was surprisingly quiet due to the VAV system’s automated reduction in flow rate. Not to mention, I didn’t smell anything bad!

I noticed that, by design, the hoods had no bypasses at the superstructure top. These bypasses were common in the hood industry at this time because it allowed constant volume systems to open an alternate air route into the hood cavity at the top of the unit while closing the sash. This feature mitigated large face velocity increases when one closed the hood sash. But this was a VAV  hood. It reduced exhaust air intake as the sash closed, eliminating the need for a bypass. Therefore, contaminant fumes were exhausted using a lower volume of air. The constant volume bypass system, and a VAV alternate, are illustrated below:

The closed bypass hood and damper system worked remarkably well. When I tested the face velocity, it remained constant until the only remaining opening was the 1” airfoil slot.

100 feet per minute (FPM) all the way down. (Remember, this is an early system!)

Yet all the stainless steel equipment inside the hood appeared to be turning rust-red after less than two weeks use. The only application these hoods were being used for was digesting limestone in small watch glasses on hot plates with 20% hydrochloric acid. Most of the time during this procedure, the sash was closed.

We calculated 49 cubic feet per minute (CFM) as the total hood exhaust during closed sash operation (all through the bottom air foil slot). This exhaust was equivalent to about 1 air change per minute (ACPM). This rate was not enough to ventilate the hydrochloric acid vapor from the hood interior, which resulted in corrosion. After further experimentation, we determined that approximately 5 air changes per minute (ACPM) was required to prevent this issue. Since the 1” airfoil was yielding 1 ACPM, we opened 4” of bypass to get 5 ACPM and…no more corrosion! There has been, since 1987, additional ways to assure VAV systems provide minimum air changes. This is also beyond the scope of this paper, but very important to hood safety and product usefulness. With acids and flammable vapors, corrosion and explosion are typically unfavorable consequences of very low minimum air changes.

See the diagram below showing how this early VAV corrosion issue was sorted:

3. Fumes escape from fume hood during raising or lowering of the sash.

While a poorly designed constant volume fume hood can lose containment during a rapid sash movement, several well–designed VAV systems with insufficient maintenance can show the same symptoms. With these VAV systems, the problem is most frequently caused by delay in measuring a condition or a delay in responding to the condition by control elements. Accordingly, the source of the issue is the functionality of the face velocity sensor(s) or damper systems which should appropriately respond to the sensors’ output.

a. Face velocity sensors are usually measuring air flow into the hood through a side-wall sensor or under-airfoil sensor and are most frequently driven by thermistors or hot-wire technology. A few designs measure sash position and infer face velocity using an algorithm and velocity pressure readings in the ductwork (two separate sensors for this example). If these sensors develop changes in sensitivity or fail, slow response to sash changes or worse may occur. Sensor deterioration or failure can be prevented through a rigorous preventative maintenance program.

b. Damper systems require physical movement to execute increases or decreases in exhaust volume. Older damper systems can slow down for a variety of reasons including actuator wear or rotator shaft wear/corrosion. Again, such mechanical depletion or failure can be guarded against through a rigorous preventative maintenance program.

c. Another less frequent cause of slow VAV sash response is the use of VAV sensors to control fan motor rotations per minute (RPM), rather than damper position. This type of system control requires fans to rapidly change RPM when throughput demand changes. Since fans usually have a significant angular momentum, RPM changes are inherently slower to achieve than damper volumetric control.

In any of the above cases, ASHRAE 110-2016 Section 6 outlines measurement methodologies and meaning of sash response time. While the range of acceptable response times is not universally agreed upon, ANSI/AIHA Z 9.5 suggests this time should be 3 seconds (section

4. While there are no duct leaks or breaches, all building spaces are showing the presence of tracer gas once any hood is operated.

I saw this situation at a rural facility in Texas with about five newly installed fume hoods. All aspects of the hoods appeared normal, except tracer gas during the ASHRAE test showed up everywhere in the building, even in the office area. We asked where the make-up air intakes for the building were located and were told all air was brought in by a single super-intake on the leeward side of the building. We also did smoke tests and watched exhaust air leaving the building through rather short stacks, skimming along the roof line, then diving over the building edge and into the super air intake. Once the intake was disabled, each hood performed normally. At the end of the day, we realized that the problem’s resolution lied within rectification of the intake system. It was either that or making the exhaust stacks taller.

5. All facility fume hoods exhibit very low face velocities. (usually seen where commissioning has not yet taken place)

A new facility with about a dozen fume hoods showed low exhaust face velocities in all the hoods. We were amazed at the consistency of the poor results because there were three separate exhaust fans involved. We finally went to the roof again and asked that the fans be turned off and “bumped”. Bumping a 3 phase fan means asking that they be given a quick “jolt” of power so the direction of rotation can be observed. In each case, the fans were running backwards. A centrifugal fan will always pull air in the correct direction, but will be less efficient if it is run backwards. Once this situation was corrected, the fans all ran at their proper exhaust level and the hood face velocities were normal.

6. Absolutely nothing appears to be wrong with the exhaust system or hood face velocity, but fumes from the hood are showing up in the lab after about one minute!

A new facility perchloric acid hood with good face velocity ran well for about 90 seconds, then the mannequin SF6 detector started showing significant tracer gas. When checked separately, this condition existed in the entire lab. SF6 also was present in neighboring labs on the same floor.

Time for a trip to the building roof.

We found that a decorative skirt had been placed around an unsightly group of “roof penetrations” to make the roof line more attractive. Inside of the skirted area were the perchloric stack and an air intake for the same lab floor. We powered down this air intake temporarily and the hood containment test was successful. We advised the building superintendent to rectify this situation. More often than not such re-entrainment problems are very common, and an additional reason to do ASHRAE 110 field tests.


The examples above are, in one form of another, very common reasons for fume hood systems “not working”.  The entire picture of design flaws, maintenance issues, or aesthetics-functionality conflicts is obviously more complex and more details can be reviewed further in the following papers on the Flow Sciences website:

  • How Should VAV Equipment Be Specified on Laboratory Hoods?
  • The Feasibility of Fume Hood Containment at 40 FPM.
  • VAV Energy Savings at High and Low Face Velocities.
  • The Overlapping Sash Bypass System

The Chart:

The Summary Chart below shows six primary containment issues that probably could represent the “80” in the 80/20 rule for fume hoods. Both the fourteen questions and six diagnoses should help building designers and project managers determine good design techniques and “tells” usually present when things do not go according to plan!

The author invites any comments on this paper and chart as additional experience will always make an experiential summary more robust!


Contact Flow Sciences

Getting What You Need in a Laboratory Hood

Issue: Many times a lab owner reflects negatively on the purchase of lab containment equipment. It was too expensive. It never worked correctly. It was inefficient to use. It was destroyed by the very chemicals it was supposed to contain.

Negative purchasing experiences such as these may be caused by poor communication. When customer meets manufacturer, relevant questions must be asked by the manufacturer and answered by the customer.

Method: After listening to the customer, a manufacturer should put this input into written form. Once complete, this document becomes a template for a product in line with customer needs.

Example: A series of such questions can stimulate a fantastic conversation with the customer. The following ten questions cover main factors that define most lab containment devices:

1)    What is the process/procedure to be done inside the device? (the application)

2)    How much space is needed for apparatus and materials? (footprint and height)

3)    How many people will be simultaneously working on this procedure? (access)

4)    Are there any chemical reactivity hazards?  (corrosion, explosion, flammability, environmental contamination)

5)     What plumbed services are needed to support the procedure? (air, gas, water, vac., other)

6)     How many outlets do you need; which voltage(s)?(electrical)

7)     Is a control system required to monitor/operate devices inside the containment area? (equipment controls)

8)     Will there be an exhaust fan operated from the containment device? (containment controls)

9)     Does some equipment need to be mounted on scaffolding? (accessories)

10)   Are there chemicals involved in the operation covered by storage requirements, such as OSHA regulation or company policies? (storage)

You notice, I omitted one frequently asked question, “What containment device are you using now?” In most cases, what we define with the ten questions may be far better for the customer than simply providing that which dissatisfied the last time.

Answering the questions:

Let’s say someone at a chemical lab answers the above ten questions according to the chart below:

Is it possible to incorporate these answers into a standard product?

The answer is “yes”.

The questions were organized in a fashion where each successive question progressively leads to a proposed solution. After question 10, a fairly clear description of the customer’s fume hood has been assembled. The final fume hood selection options can be visually displayed, as seen in the example graphic below.

This illustration is taken from a worksheet Flow Sciences uses frequently to form a visual picture of what a customer wants. We use the worksheet to record interview questions and consult with the customer to formulate, and eventually resolve, an understanding of the customer’s needs. Ultimately, Flow Sciences produces a “blueprint” of the customer’s solution for the manufacturing portion of the process.

All preferences and options are subsequently transformed into categorical data. The resulting data accelerates the process of manufacturing the unit. The total number of options available on a standard fume hood are quite robust, as shown in the chart below:

Simply starting with the above chart would be a fallacy. The options displayed above do not resemble customer needs obtained during consultation.  The chart does, however, allow Flow Sciences to effectively communicate to our manufacturing sector the product that best fits the customer, based on the information gathered from the customer interview.

So, if in life you don’t always get what you want, our customers always get what they need through this approach to data-gathering. Our customers are offered the luxury of getting the best product, built correctly the first time.


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Flow Sciences, Inc.’s SAF T FLOW™ Fume Hood Receives Outstanding 3rd-Party Certified EN14175 Fume Hood Containment Results

LELAND, NC, June 7, 2018, — Flow Sciences, a leading provider of containment systems for laboratory, pilot plant, and manufacturing is now shipping the SAF T FLOW™ Fume Hood an addition to its expanding line of standard enclosures.

Dr. Robert K. Haugen, Director of Product and Technology Development at Flow Sciences Inc., today announced that the SAF T Flow™ 6-foot fume hood has received 3rdparty certified EN14175 fume hood containment results from Raleigh, NC based Exposure Control Technologies (ECT). The results showed that under any containment required by EN14175, no observable tracer gas left the fume hood, yielding the lowest possible containment numbers of less than 10 ppb (parts per billion), the detection limit of the instrument.

Randy Blew, of ECT, states in the introduction and summary of the report “Results of tests revealed that the Flow Sciences hood met all acceptance criteria as described herein under all test conditions.” 1

  1. “Results of DIN-EN “As Manufactured” Tests on One Laboratory Fume Hood,ECT, inc., March 1083 p. 3


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Two Well-Known Fume Hood Containment Tests: ASHRAE 110 & EN14175...A Comparison

Two Well-Known Fume Hood Containment Tests: ASHRAE 110 & EN14175…A Comparison

Dr. Robert K. Haugen, Director of Product and Technology Development

Flow Sciences, Inc. 

2025 Mercantile Drive

Leland, North Carolina 28451



The demand for effective fume containment devices is truly international. Many manufacturers of such devices have a global customer base. These manufacturers must demonstrate effectiveness of their products through successful fume hood containment testing.

There are, however, two widely used and quite different fume hood containment tests. These two tests are ASHRAE 110-2016 and EN17145 Part 3. The former test has been developed in the US; the latter is Pan-European.

This fact frequently confounds international comparison of two products whose effectiveness is reported using different tests. This situation is even more serious if these products are participating in the same tender evaluation process.

The worldwide map shown below depicts this distribution of containment tests. Countries where both standards are used (orange stars) present unique problems for fume hood manufacturers.

The map confirms each containment test is widely used in the region where the standard was created. More distant areas (orange stars) use both standards. When the two containment test standards come into conflict in these regions, comparing containment results of two products tested differently creates severe commercial and competitive issues. Since both tests are so different, we should really try to reach a consensus on how to select products evaluated using such dissimilar criteria. Let’s first look at these standards more closely.

The Two Containment Test Approaches:

 A. ASHRAE 110-2016

The ASHRAE 110-2016 test traces its roots to research published by the American Industrial Health Association (Knudson and Caplan) in 1982. 1

Hood face velocity is measured using a thermal anemometer and a sash plane velocity grid specified in section 6.2 of the standard. Sulfur hexafluoride (SF6) is diffused into a fume hood and the quantity that escapes into the mannequin breathing zone is measured using an Infrared Spectrophotometer or Ionization Technology. An illustration of the basic setup is shown below: 2

The ASHRAE 110-2016 test procedure employs 100% sulfur hexafluoride as the tracer gas. The gas diffuser (tall circle) is set at a supply pressure of 30 PSI with a diffusion rate of 4 lpm. Tests are run with a mannequin for 5 minutes and SF6 concentrations in the mannequin breathing zone (wide circle) recorded. An SME (sash movement effect) test is run for a total of two minutes and includes opening and closing the vertical sash twice in 30-second intervals over the two-minute run. Tests are run and SF6 concentrations in the mannequin breathing zone recorded.

Although ASHRAE 110 does not define a pass-fail level for the test, AIHA Z 9.5 sets forth a suggested pass/fail level of average breathing zone tracer gas of 0.05 PPM 3.

B. EN 14175; Part 3

While EN14175, Part 3 and ASHRAE 110 both measure fume hood containment, they do this quite differently using very different equipment and calculations.

En14175 has a total of six sections:

*Hood vocabulary

*Hood safety requirements

*Hood containment testing

*Testing on-site methods

*Installation & Maintenance

*VAV performance testing

We will focus only on Section Three which defines hood containment and the evaluation of this performance characteristic.

While the EN14175, part 3 test method evaluates and reports levels of escaped tracer gas, it also generates a series of unitless numbers called Containment Factors which represent hood tracer gas flow rate divided by the product of extract rate times escaped tracer gas concentration. In most reports written today, either escaped tracer gas concentration, and/or the containment factor are used to quantify containment performance.

The EN 14175; Part 3 test uses a 10% sulfur hexafluoride – nitrogen mixture with a total delivery rate of 2 LPM for interior plane test (using a 9-point diffuser sampling array); a rate of 4.5 LPM for the exterior plane and robustness test, and a [(5 to 8) / 1,000,000]) fraction of the hood exhaust rate flow for the air exchange efficiency test.

These challenge rates (CR’s) are much smaller than the challenge rate of 4 LPM of 100% SF6 used in ASHRAE 110; see chart below:

The 2 to 6 LPM flow rate of 10% SF6 converts to a pure SF6 challenge rate of 5% to 15% of the ASHRAE 110 challenge rate of 4 LPM of 100% SF6!

Details of the Actual EN 14175 Tests:

1)Gas diffuser array for Exterior Containment, Robustness, and Air Exchange Efficiency Tests.

2) Exterior sampling array & samplers:

“Exterior Plane” is defined as the outermost portion of the hood frame housing the sash and consists of a variety of sampling points depending on the dimensions of the sash opening.

3) Interior Plane sampling array & diffuser for interior plane containment:

The nine interior sampling points and single diffuser are located on a single device that is placed in several locations at the hood sash plane. The diffuser (circled) for this test is in front of the sampling grid on the same assembly. The sampling ports are on the sash plane.

4) Sensor

The “Gas Analyzer” used in EN14175 is generically described in section 5.3 and has these requirements:

a) A detection level of 10-8  volume fraction or less (10 ppb by volume, or 0.01ppm)

b) A time constant of less than 15s

c) A data recording capability of 1 reading every two seconds or less

d) For the Flow Sciences test, an ionization leak detector compliant with points a-c (shown above) was used.

5) Robustness Test

To carry out this test the sash is set to a specified sash opening position. After a period of 60s of tracer gas flow, the movements of the black rectangle wheeled cart (see left of illustration above) across the fume hood front completed for six crossings. The path of movement should start and end at a point 600 mm on each side of the fume hood. The time between each crossing should be 30s. The test gas concentration is measured and recorded. The measuring signal of the gas analyzer is recorded for 30s after the rectangle movement stops.

6) Air Exchange Efficiency Test:

The air exchange efficiency test uses a flow rate which yields a fume hood interior gas concentration of 5 – 8 PPM measured at the device duct collar. Gas is shut off when steady-state concentration is reached. Concentration / time data is recorded until interior fume hood SF6 concentration reaches 20% of the steady state value ~ (1 – 2 PPM). Time for this to occur is noted.

An efficiency number is then calculated as a ratio of observed and ideal air change rates of the device. Because this number does not evaluate containment, and has an unclear relationship to hood efficiency, it will not be discussed further in this white paper.

7) Calculations:

The average reading of all containment testing techniques mentioned above is recorded and plugged into the following formula for Containment Factor:

8) Pass-Fail levels for EN 14175 Data

Note, data on this German chart uses a comma instead of a decimal point which is the custom in many European countries.

It should be noted that most published containment values for commercial products are far lower than the limits expressed in these two sources cited above. Most fume hood manufacturers publish data having no detected values whatsoever for escaped tracer gas during any test. This is Flow Sciences experience with this test as well!

9) Springer6 expresses several issues with the formula for calculating Containment Factors. Remember, the larger the CF, the “better” the containment is supposed to be. Consider the following:

a) To most reviewers, the term “Containment Factor” implies a number whose magnitude indicates degree of containment. In actuality, CF combines the ability to contain with how much exhaust the system is using.

10) What has actually been seen in the field when data are obtained and CF is calculated?   Here’s a data table using the BS EN14175 Part 3 procedure on an actual fume hood 4:


The exhaust rate, Q, is in the denominator of this calculation. Therefore, the equation for Containment Factor gives a larger (better) number with smaller exhaust rates.

You can see how the CF “magic numbers” 5613 and 3426 pop up everywhere because the detection of SF6 is zero, but the “zero” has been replaced by the instrument detection limit of 0.01 PPM! Also note the non-standard use of “>” to dignify the four significant digits in the containment factor.

On this table, the lower face velocity 0.3 m/s shows a “better” Containment Factor than 0.5 m/s. This number has been shown higher simply because the exhaust quantity has gone down while the escaped SF6 remains undetectable. This anomaly gives a misleading impression that containment characteristics have improved at the lower face velocity.

Ali Bicen and others have attempted to stratify the containment Factors into a banding scheme shown below: 5

Note that outer plane Containment Factors (Protection Factors) trend lower the lower the face velocity (ie class) of fume hood.  (Class 1, Class 2, Class 3, the lowest class) This banding scheme shows the expectation that higher face velocities will yield higher Containment Factors (larger numbers), but as we have seen from the example in # 10 above, experiments and observations have shown that this is not usually the case!

Waldner’s SteffenSpringer states quite clearly6 the inappropriateness of the Containment Factor using an analysis which I restate below, starting with the formula for calculating the factor defined earlier:

He makes the following comments:

1) The structure of the equation is very simple.

2) Theoretically, the result means: the higher the factor the higher the containment of the fume hood.

3) The magnitude of Containment Factor is dependent on three values:

a) Flow rate of tracer gas

b) Extract flow rate of fume hood

c) The mean tracer gas concentration inside and outside the hood (the latter is the only value in this equation that relates to the ability of fume hood to contain).

4) According to EN14175, CFR should be rounded to the nearest integer and it must be indicated “if the result is limited by the detection limit of the instrument”

5) Now here is where it gets interesting! With q, the tracer gas flow rate, being always constant (stipulated in EN 14175) and an assumed detection limit of 0.01ppm of the measuring equipment, the only variable remaining is the extract volume of the fume hood since no detectable tracer gas escapes. Is this result (CF calculated as described before) suitable for an objective comparison of fume hood containment?

Springer does not believe the containment factor is suitable as an objective indication for fume hood containment unless all models in question are tested under the same conditions, with the same extract volumes and with same test equipment. If only one of these variables is not the same, different Containment Factors for the exactly same fume hood performance will be calculated! For this reason, the Containment Factor does not enable the user to select the best hood based on containment performance.

These problems with CF have caused evaluators using EN 14175 – 3 to evaluate a hood based on the ppm of escaped tracer gas(ϕ), rather than the Containment Factor CF9

The remaining problem is that a majority of EN14175 tests show NO tracer gas escape under any of the many tests outlined above. In other words, EN14175 has a great deal of trouble differentiating between fume hood performance from one design to another.

Andy Sinnamon echoes this sentiment on linkedin, saying:“(my Company) went through this process some time ago. The lack of a mannequin and the dilute tracer gas makes a pass virtually guaranteed for most any hood design.”11

I concur the test differentiates poorly between performance conditions at different face velocities, but I am not sure about the test’s ability to detect a faulty hood, since we probably would not see such tests published.

Summary of Significant Issues with EN 14175:

1) The complexity of EN14175 equipment:

The most accurate way of judging performance of fume hoods is by assessing the ‘containment’,ϕ, CF is not a useful factor.

Because of equipment complexity, the EN 14175-3 containment test is usually performed only at design stage (in a test lab). Actual construction practice has evolved into doing field commissioning of a delivered fume hood with simpler “tests” not part of EN 14175 7.

The only situations when the EN 14175-3 test is performed on an installed fume hood is when other lab conditions produce doubt that the hood is working. “For example, when smoke tests have suggested turbulent air movement within a hood (despite the average face velocity being acceptable) and instances of complaints of unpleasant smells emanating from a fume hood (despite the satisfactory face velocity measurements).” 8

2) The unclear meaning of the Containment Factor CF:

A fume hood is built to protect people from hazardous materials using exhaust. Depending on the design and the amount of extracted air, any containment device should be able to keep hazardous fumes inside and protect people in front of the device opening. How effectively a fume hood can “contain” is allegedly depicted by what EN14175-3 calls the Containment Factor. The better a fume hood can hold a certain containment with less air, the larger the Containment Performance Factor is supposed to be.

However, undetectable escaping tracer gas levels lead to a factor of indeterminate value which is not comparable to other instances where different detectors are used. Due to this, two identical fume hoods with the same amount of extracted air and the same opening in the front can have different Containment Factors if detectors of differing sensitivity are used.

In the selection of fume control devices, safety of the operator (low quantities of escaped fumes) is of the highest importance, not an algebraic combination of containment and exhaust volume data. In the writer’s opinion, a containment evaluation should not use a hybrid value like the Containment Factor to quantify hood performance.

The author therefore believes that the focus in EN 14175-3 should be on detected escaped tracer gas (ϕ) at a specified face velocity, not the containment factor (CF).

The University of Cambridge notes that the “type tests done according to EN14175-3 are clearly made in compliance with ideal conditions. This means that even regularly occurring disturbances are not taken into account and fume hoods with applicable very low face velocity provide outbreaks if there are any minor disturbance occurs.” 8

As discussed previously and noted by Egbert Dittrich, the Containment Factor is not suitable as an objective indication of fume hood containment unless all models in question are tested under the same conditions, with the same extract volumes and with same detector equipment. Only one of these variables not being the same, will lead to different containment factors. In practical terms, the Containment Factor does not enable the user to select the best hood based on the value of CF. 7

3) The inability to differentiate between fume hood performance.

Unless and until we can measure escaped tracer gas better, virtually all published data for hoods tested with EN 14175-3 yield the same result for all escaped tracer gas tests. Zero. (that is, 0.00 PPM)

My experience is ASHRAE 110-2016 generally shows measurable low tracer gas escape. Ability to produce finite readings has allowed developers to tweak designs to some degree and have data which show improved performance. 12

ASHRAE 110-2016 and EN14175 Part 3 Compared:

The author believes both tests could be improved. The ASHRAE 110-2016 test appears to have a much more substantial SF6 challenge, yields more differentiable results, and is an easier test to perform in the field.

The EN 14175-3 test measures more potential containment escape points. It also has a standardized robustness challenge employing a flying rectangle to simulate a walk-by. The table below summarizes many of these test comparisons.

The Impact of 2 Standards on Brand Competition. 

Companies that do international business must be prepared to test hood performance with whatever containment test is specified on a case-by-case basis. Both containment tests have unique strengths and weaknesses.

Because the tests are so different, conversion of one test’s data into projected readouts from the other test’s procedures is a fool’s errand.

A comment on objectivity. The larger number of “good” ASHRAE 110 aspects in the above chart is a reflection of the author’s predominant use of ASHRAE 110-2016 test through his entire career. It should not be viewed as “proof” that one test is better than the other.

Nor should the opinions of others who are commercially committed to one test or the other.

Attempts should therefore be made to establish a single standard for the Twenty First Century world of lab construction. Such a standard would facilitate evaluation of containment products on an even playing field for all competitors, wherever the laboratory is located.


  1. Influence of room air supply on laboratory hoods, October 1982, Knowlton J. Caplan, Gerhard Knutson, American Industrial Hygiene Association Journal
  2. ASHRAE 110-2016, p. 13.
  3. ANSI AIHA Z 9.5 – 2012, section, p 79
  4. Type testing of fume hood according to EN 14 175-3:2004, Institut fur Industrieaerodynamik GmbH, Certificate No. 1/FC-Z81/P3/06/13, 2013
  5. Institute of Local Exhaust Ventilation Engineers – Information Day – 17 May 2016, PowerPoint presentation, Melvyn Sargent, Lab Containment Services LTD
  6. BS EN 14175-3:2003 Containment Factor deciphered, Steffen Springer, Jan. 2011, PowerPoint presentation.
  7. Egbert Dittrich, The sustainable Laboratory Handbook, Wiley, 2015
  8. Fume Hoods, Guidance for Safe Use, University of Cambridge, October 2016 https://www.safety.admin.cam.ac.uk/files/hsd029c.pdf
  9. University of Birmingham Health and Safety Department, Hazardous Substances Policy Schedule 3.8, Supplement 1, https://intranet.birmingham.ac.uk/hr/documents/public/hsu/hsupolicy/hs15/HS38LEVSupplement1.pd
  10. Air Change Measurements Using Tracer cases, Chemistry, Emission Control, Radioactive Pollution and Indoor Air Quality, 2011,David Laussmann and Dieter Helm
  11. https://www.linkedin.com/in/robert-haugen-22918546/detail/recent-activity/shares/
  12. The Fume Hood Product Life Cycle: A Cost of Ownership Analysis Robert K. Haugen, Ph.D., Director of Product and Technology Developmen, Flow Sciences, Inc.10/31/2017


Contact Flow Sciences


How Should VAV Equipment Be Specified on Laboratory Hoods?

How Should VAV Equipment Be Specified on Laboratory Hoods?

Dr. Robert K. Haugen, Director of Product and Technology Development

Flow Sciences, Inc. 

2025 Mercantile Drive

Leland, North Carolina 28451



Recently, there has been an increasing interest in Variable Air Volume (VAV) fume hood control systems.1 This paper will define such systems in the most elemental sense.  The scope of HVAC systems affected by fume hood VAV will then be detailed. Finally, I will make recommendations regarding the best way to specify such systems to get the best overall finished product from all building suppliers involved.

VAV Systems Defined and Explained:

VAV chemical fume hoods vary the volume of room air exhausted while maintaining the face velocity at a set level down to the lowermost sash openings. Different VAV hoods change the exhaust volume using different methods; exhaust dampers may open or close based on sash position, or a variable speed blower can change fan RPM to meet air-volume demands. The purpose of reducing hood exhaust volume as a function of sash position is to give lab designers an opportunity to exhaust less conditioned air while maintaining proper face velocity, saving energy expense, and promoting sustainability.

ASHRAE 110-2016 addresses VAV hoods in the following manner in Section B3.9: 2

“While the majority of laboratory hoods are installed on constant-volume systems, a growing number of laboratories use VAV supply and exhaust systems. These VAV systems can reduce the volume of air exhausted from the laboratory. It is important to ensure that the VAV systems are properly designed, calibrated, and maintained. The VAV systems, just like all other components of the HVAC system, must function correctly to ensure that fume hood performance is not compromised.”

VAV hoods are connected electronically to the lab building heating, ventilating, and air-conditioning system (HVAC), so hood exhaust and room supply are balanced. In rooms with multiple hoods, labs may become positively or negatively pressurized if this balance in flow is not accomplished.

An “unbalanced lab” scenario is where air exhaust and air supply are significantly different. A lab area at a large positive pressure can be potentially dangerous, particularly when this pressurized lab contains an accident and fumes are “blown out” of the lab into other critical spaces.  Most newer VAV hoods feature monitors and/or alarms that warn the operator of such positive situations as they can lead to unsafe containment conditions.2    The boundary level for an unacceptable positive lab pressure is typically set at 0.1” w.g. (about 0.00036 pounds per square inch [PSI]).3  While measurable, this number is a challenge to accurately measure and not knowing this value will leave lab personnel without warning.

Lab pressurization is only one example of why flows in a VAV system must be accurately measured. The elements shown in the lab schematic below all must be measured and regulated with accuracy for a safe and functional VAV fume hood exhaust system 4:

The four boxes in figure 1 highlight four key elements of any VAV system:

1) Red box shows fume hood and its VAV damper.

2) Blue box shows room exhaust VAV damper. In some cases, this damper is not included because room exhaust is all originated by the fume hoods.

3) Green box is the room make-up air damper, room differential pressure sensor, and supply duct.

4) Purple box (rounded corners) is the control module.

5) It should be added that the depicted system uses dampers rather than VFD multi-RPM exhaust/supply fans. VFD designs are less frequently used because often they have a response time which cannot keep up with rapid and unpredictable sash movements.

Assuming boxes 1-3 are properly designed and yield exhaust response times within a 1-2 second range, the purple box becomes the real challenge. This pressure control module must vary exhaust and supply CFM to provide design face velocity to the fume hood while increasing or decreasing room make-up air to achieve a slightly negative room static pressure differential. Large accidental toxic discharges inside a lab should NEVER be allowed to be oozed into neighboring labs by a lab space wrongly under positive pressure.

Over the past thirty years of increasing applications of VAV technology, a variety of operational problems have been documented with fume hood VAV systems similar to that shown in Fig. 1:

1) Elements within a VAV system must have sensor/valve lag times adjusted in such a way that the system will not degenerate into a condition where labs cycle between over and under pressurization.

2) To accomplish stability, response times of each element must be rapid enough to assure changing sash positions will quickly yield a steady-state, balanced system with acceptable fume hood face velocities.

3) Given the defining control element of any VAV system is the actual fume hood face velocity achieved at a certain sash position, the face velocity measurement technique should not inferentially measure this variable without proof such an inference is valid under lab conditions. The most plausible criticism of VAV is some relevant variables critical to operator safety and air exhaust/delivery stability are frequently not directly measured. These variables may include:

a) Face velocity of the fume hood

b) Exhaust CFM of the fume hood

c) Total room exhaust

d) Total room supply

e) Room static pressure differential

In spite of the issues reviewed above, VAV fume hoods are a fact of life and are increasingly becoming a way of life in 21st century lab design.5,6   For this reason, all companies that manufacture fume hoods must offer high efficiency VAV hoods and be prepared to compete in the open marketplace to sell them and effectively install them into HVAC systems largely furnished to the jobsite by others.

From our product’s perspective (fume hoods), this market reality requires clear performance specifications and subcontractor responsibilities that have been established before VAV system elements are specified, purchased, and meshed together. Architects, mechanical engineers, and HVAC contractors should assume the responsibility for stating the duties of each subcontractor toward achieving a functional, stable, and safe fume hood exhaust system.  This system must be far more than a collection of autonomous independently tested components. At least three key elements in such a system must work together:

1) A high efficiency fume hood with great containment and controlled face velocity 7

2) Make-up air room supply and exhaust properly located for room air flow stability

3) An automated control system that maintains each lab at the proper negative pressure, regardless of fume hood sash position(s).

Practical Requirements for Specifying a VAV exhaust System:

The researcher makes the following recommendations regarding specifying fume hood VAV systems.  These steps apply to all subcontractors who are together responsible for providing an effective laboratory ventilation system:

1) The top priority for any fume hood VAV system must be safety. The Author has participated in the development of fume hood containment standards for the last 30 years using the periodically updated ASHRAE 110 standard.  The most recent version of this fume hood containment standard is ASHRAE 110-2016 8.  The standard has specifically stated ways to evaluate VAV systems which should be followed (Sections 6.2 and 6.3). While the ASHRAE test has no containment pass-fail standard, ANSI/AIHA Z 9.5-2012 has set a pass-fail factory as manufactured (AM) standard of 0.05 PPM 9 using the ASHRAE 110 procedure.

This pass-fail level has created some controversy. Lab Planner Jerry Konigsberg thought the pass-fail number too large, while consultant and lab designer Gregory Muth regarded it as too small. Mr. Muth states that many applications of fume hood containment should not require the 0.05 PPM control level standard, but “something higher.” 10

Making the specified containment level higher is problematic.  First, if hood application determines where the containment performance bar is to be set, what happens when the hood application changes? Second, no hood smoothly transitions from a lower to a higher control number as one lowers the design face velocity.  Instead, containment level abruptly fails at some point and yields new performance levels thousands of times higher. Like concrete bridge supports, we are taking chances if we set the acceptable test level barely above the failure point.

2) While fume hoods are assumed to be “furniture” in a traditional specification format, their performance must be evaluated as part of the larger lab ventilation picture in a modern VAV specification. To gauge fume hood containment performance, a proper air flow environment must be established and then hood-validated using ASHRAE 110 containment testing. Many poorly designed or calibrated components of a VAV system might cause severe system containment issues in field commissioning tests. This would generally mean the hoods are not working for reasons located elsewhere in the exhaust system and the reason for the subpar performance needs to be identified and corrected using other trades.

For example, if exhaust fans are not running, the hoods won’t work. If sensors are not properly measuring flow parameters, the hoods may not work.  Each VAV component must be properly synched with all other VAV containment system input elements before containment is evaluated.

3) Finally, the overall HVAC contract should include work necessary to assure system stability and fume hood containment. System commissioning is a team sport. Any team needs a leader. All pieces of the HVAC puzzle should function together properly. A poor lab designer who has not thought out the HVAC overall structure may not understand how it should work and will be in an impossible position to supervise and determine fixes when building commissioning reveals new performance issues.

Such a stability assessment should start at local control boxes and work its way out into the tentacles of the system. Knowledge of system dynamics is essential.

In conclusion, lab VAV fume hoods must be specified in coordination with other vital elements of the fume exhaust system.  Air dampers/valves, exhaust fans, sensors, thermostatic controls, and the BMS controlling lab pressures are all critical in producing a safe lab exhaust system.

If it is not the contractual responsibility of a single party to “get the system running”, the building HVAC system can easily create migraines at the end of a lab project.


  1. R&D Magazine, 10/21/2009, The Great Fume Hood Debate, Paul Livingstone
  2. Dale T. Hitchings, PE, CIH, Laboratory Space Pressurization Control Systems, 2001, http://www.safelab.com/FACT_SHEETS/Pressure.pdf
  3. ANSI/ASHRAE Standard 110-2016, Methods of Testing Performance of Laboratory Fume Hoods, March 31, 2016,
  4. Wikipedia, Fume Hood, Variable Air Volume.
  5. http://ateam.lbl.gov/Design-Guide/DGHtm/vavsystems.htm
  6. Greg Muth, Laboratory Design News, Sustainable Lab, 10/12/2015, https://www.labdesignnews.com/article/2015/10/fume-hoods-lab-design
  7. Gordon Sharp and Others, R&D Magazine, 2010, Airing Out Laboratory HVAC, pp1-3, http://www.aircuity.com/wp-content/uploads/RD-Magazine_Airing-Our-Lab-HVAC_2010_08_Eprint.pdf
  8. ASHRAE 110-2016 and ANSI/AIHA Z9.5 together establish testable minimum safety standards.
  9. ANSI-AIHA Z 9.5, Section2.4.1, explanation column.
  10. R&D Magazine, 10/12/2015, Fume Hoods in Lab Design, Hock, Lindsay, p 1 of 7, https://www.rdmag.com/article/2015/10/fume-hoods-lab-design



Contact Flow Sciences


The Feasibility of Fume Hood Containment at 40 FPM

The Feasibility of Fume Hood Containment at 40 FPM

Dr. Robert K. Haugen, Director of Product and Technology Development

Flow Sciences, Inc. 

2025 Mercantile Drive

Leland, North Carolina 28451

V 1.1; 12/28/2017


Flow Sciences is a company that designs, tests, and manufactures a very diverse line of laboratory containment devices.

Energy conservation appears to be the most significant issue involving containment devices in the 21st Century.  Over the last two decades, techniques to improve containment while reducing exhaust from fume hoods and other exhaust devices have overwhelmed all other aspects of containment exhaust research.  Innovations have included reduced sash openings, self-closing sashes, reduced volume through variable air volume (VAV), and fume hood nighttime volumetric setbacks. 1

When ball-parking lab exhaust cost, one can use $10/CFM/year as a “first guess”.2 A single 5-foot exhaust hood extracting a classical 100 FPM exhausts about 1000 cubic feet per minute (CFM), for an annual energy expense of $10,000! 3 Most lab people, even users of hoods, are astonished when they first hear these numbers. The number is this large because each cubic foot of air brought into the lab must typically be heated or cooled (money), dehumidified (more money), distributed through ductwork (more money), either redistributed and purified (still more money), or exhausted and replaced with new, outside air (still more money).

Reducing the quantity of air passing through such an exhaust cycle can obviously reduce the expense of operating it. This would be good for economy. This would conserve energy.  This would move us toward sustainability. This would be very good indeed!

One way to reduce exhaust volume is to lower fume hood face velocity. Older standards called out an 80 – 100 feet per minute (FPM) fume hood face velocity as being a “safe” number.4   Newer “high efficiency” fume hoods can operate with documented safe containment down to 60 FPM according to their manufacturers. 5, 6, 7

Unfortunately, all good things have their limits.  Several recent job specifications have called out a 40 FPM face velocity and require testing demonstrating containment at this level. Such a low face velocity could save even more energy, but “passing” the ASHRAE 110-2016 As-Manufactured test, the typically-specified containment test in the US, may not be proof the fume hood will be safe when used in operating labs under working conditions.

40 FPM Tests Already Done on the Flow Sciences Fume Hood:

We will now go through the good and bad news of all of this in a more academic fashion and see if there is a clear path forward to save even more energy and money with a 40 FPM face velocity.

Flow Sciences, in response to customers who requested test data on fume hoods tested at 40FPM, have already run these tests on our Saf T Flow high-efficiency fume hood.

All test data at 40 FPM passed the ASHRAE 110 and HAM tests at the AIHA Z 9.5 levels cited with the chart.  In spite of this, FSI feels tests at these low face velocities need extra clarification. 

Qualifications on the 40 FPM Face Velocity Test Results:

Rather than criticizing a particularly low suggested fume hood face velocity, let us consider possible threats to any well-designed low velocity fume hood by making a ZERO assumption. That is, let’s assume our fume hoods are operated at 0 FPM. (Yike!) What could go wrong? We must also place this gedanken hood into an actual building environment.

This is a producto ad absurdum (PAA) approach.  Assume something absurd to highlight resultant difficulties, then see if similar issues will occur under slightly less absurd conditions (i.e.40 FPM).

Here’s some of the PAA things that will go wrong at 0 FPM:

  • Fumes would not stay inside the fume hood, but would move into the room as air vectors and simple molecular kinetic energy would now have supremacy over the zero fume hood face velocity. This scenario is Dire.
  • “Bad” air from contaminated labs with no fume exhaust would now spread everywhere, carrying contagion into every area of the entire building. This scenario is Dire’s first cousin.
  • Room thermostatic control would be unstable since modern buildings circulate conditioned air into a lab area while consistently pulling “old” air out of an area and then exhausting or recirculating it. Fume hoods are frequently the primary or exclusive exit point for “old” lab air. Without this exhaust it may be impossible to control temperature or humidity in labs. “Sensible Heat” in any lab area is much higher than in an office environment because of illumination, ovens, flame emission spectrometers, hotplates, and computer waste heat. This scenario of meager air changes is uncomfortable and may impact experiments requiring controlled temperatures.
  • Hood interiors and their contents would become corroded under a wide variety of applications that release corrosive acid vapors, free radicals, or transition molecules into the containment area. This scenario is expensive.
  • Stuff could blow up inside fume hoods. Many organic chemicals have lower explosive limits (LEL’s) that when reached, will cause eruptive explosions when in the vicinity of sparks or other sources of activation energy. This scenario is literally explosive if solvents spill, boil over, or are released into the hood interior during reflux.

Of these containment and HVAC issues, only numbers one and two are measured by the HAM and ASHRAE 110 containment data cited. The last three scenarios, thermostatic control, interior hood and contents corrosion, and explosions are dependent on building conditions (HVAC system) and hood minimum flow rates.

A variety of scenarios will occur based on the minimum CFM assigned by the building HVAC engineering group to each hood.  This problem is particularly serious with variable air volume (VAV) fume hoods. As one closes a VAV fume hood sash, the exhaust will be reduced to maintain the face velocity specified (40 FPM, for example).  If no other factors are programmed into the VAV system, this would mean that at full sash closure, many hoods with no bypass would exhaust virtually no air at 40 FPM. A 48” FSI hood with no bypass and a 1” airfoil opening would have the following full-closed exhaust:

Cubic Feet per minute = CFM = 40 FPM X (38.5” X 1”)/ (144 sq”/sq ft) = 10.7 CFM

And additionally:

Air Changes per minute = ACM = 10.7 CFM / ((38.5” X 24” X 48”)/(1728 Cu in/Cu ft) = 10.7 / (44,352/ 1728) = 10.7/25.7 = 0.42 ACM= 25 ACH (Air Changes per Hour).

As stated in the footnotes, I have evidence using the LEL (lower explosive limit) level for acetone and observed corrosion effects of HCl(g), that the air change rate inside a fume hood should never drop below 5 ACM (300 ACH). For the record, my 300 ACH minimum number is not unanimously agreed upon in the literature.8   AIHA Z9.5, for example, cites a range of 150-375 ACH. However, the VAV hood cited above at 25 ACH is way lower than even the range cited by AIHA Z 9.5.

These sash-closed corrosion and explosion scenarios at low exhaust levels are very significant with VAV hoods, as little savings are realized with the CFM-hungry sash open.  It is essential that the minimum air change rate with sash closed be agreed to by lab safety and HVAC engineers because it is likely in new labs that the sash-closed position will be encouraged by lab safety and building engineers. This closed sash setting should maintain enough CFM throughput to clear the hood of explosive or corrosive levels of fumes (150-375 ACH). 10

Here’s the good news. Adding a small bypass to the high efficiency hood will increase the minimum air change rate significantly. Such a properly designed bypass can also improve containment.9 If such a bypass system is combined with an algorithm in the VAV controller to guard against sub-standard minimum CFM, two risk charts for hood operation can be set forth as shown below:

The above charts attempt to approximate what would happen at face velocities above zero and reflect my assessment, based on test room observations, of the five danger areas as velocities are increased. Red is bad.  Yellow could be bad in the presence of high fume-generating procedures. Green will probably work okay in most cases.  Because all lab experiments could encounter a variety of other negative scenarios outside of the five I outlined, green conditions are only green if all other design and safety issues are judged favorable.

Other Conditions Affecting High-Efficiency Hood Containment:

  • Aerodynamic overall room layout

Locations of room make up air ceiling gratings, fume hoods out of high foot traffic areas, closed laboratory doors, hood sash discipline, are all within design requirements.

  • Overall building commissioning and periodic re-checks

With VAV systems, but with CV systems as well, room pressurization, hood flow and system response to sash adjustment, duct integrity, and hood & room sensor accuracy should all be periodically verified.

  • Re-entrainment

Since low volume fume hoods will produce exhaust streams with a higher concentration of fumes, the exhaust system should both dilute exhaust streams and insure the exhaust stack velocity allows the fumes to clear the building and remain free from air intake areas.

  • Building HVAC exhaust alterations must be carefully undertaken

Many times the stewardship of a variable air volume system is not consistent.  Obviously the addition or elimination of exhaust hoods will change airflow parameters and require modification of HVAC control parameters. In any facility with HE low velocity hoods, changing the hoods must require an adjustment of control parameters.

  • Power outages or blown circuits

In the US and overseas, many different things can cause power grid loss or building sector outages. During commissioning and re-checks, HVAC and VAV control and tracking operations should be simple and forthright, and not require re-programming or subsystem resets after a power outage. The easy re-establishment of all HVAC functions should be tested and verified before turning the building over after construction.


1) Traditional containment testing shows 40 FPM is sufficient at 18” to contain fumes for Flow Sciences constant volume HE fume hoods.

2) Under VAV operating conditions, extra care needs to be taken regarding programmed exhaust volume at full sash closure. While exhaust may be contained, either explosive or corrosive issues within the fume hood may occur under these conditions. This issue is of considerable importance since wide disagreement and uncertainty exists in the literature about how many air changes per hour are adequate in a closed VAV fume hood (150-375 ACH).

3) As hood exhaust numbers are lowered, overall building HVAC issues will require frequent and consistent monitoring of building control systems whenever inevitable additions or changes to the fume hood population occur. With energy conserving VAV or CV systems, adding or removing fume hoods from a lab building may require system-wide adjustments.


1) https://flowsciences.com/fume-hood-energy-savings-low-hanging-fruit

2) This approximation falls between a low of $5.00 by Safelab (http://www.safelab.com/FACT_SHEETS/Fact4.pdf) and a high of $15.00 by Cal OSHA (http://docketpublic.energy.ca.gov/PublicDocuments/17-BSTD-01/TN217908_20170607T113738_6617_Laboratory_Fume_Hoods_Presentation.pdf)

3) Constant volume hoods at 100 FPM face velocity 24 hours a day.

4) Industrial Ventilation A Manual of Recommended Practice, 19th Edition,recommends 80 – 100 fpm face velocity with a full open sash depending on quality of supply air distribution and uniformity of face velocity.

5)Flow Sciences Lab Design brochure, 2017, P2.

6)ANSI/ASHRAE 110-2016 Containment Testing of The 4 Foot Safe-T Flow Chemical Fume Hood Including Data for Ultra-Low Face Velocity of 40 FPM at 18” Sash Opening, Flow Sciences, 2017

7)Summary, Containment Testing of Safe-T Flow Chemical Fume Hoods 5/31/17

8) ANSI/AIHA Z9.5-2012 p25 cites a range of 150 to 375 ACHas range of acceptable minimum CFM for VAV fume hoods.

9) https://flowsciences.com/overlapping-sash-bypass/

10) Low volume VAV settings are really experiment-sensitive. Very high volume experiments may cause issues not originally considered dur