chemical fume hood

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 Material Appearance Particle Size Density (g/cm3) Quantity Used
Sulfur hexafluoride Colorless Gas ~ 3.12Å diameter 0.0062 4L / min
Methylene Chloride (DCM) Colorless liquid or gas ~ 2.94Å diameter 1.33 (l), 0.0035 (g) 3 x 250 mL
Lactose Monohydrate White, crystalline powder <250 µm (≥99%) 1.54 3 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.


Test FAF483655VAA
Average Airflow Velocity (fpm) 80.75 ± 4.95
Low Volume Smoke Rating Good
Large Volume Clearance Time (s) 25
Average TracerGas Reading (ppb) Static 0.00
SME 0.00
HAM 2.80

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.

ppb µg/m3
Release rate concentration 364,161 2.18e6
Escape STEL 2.80 16.74
Escape TWA 0.015 0.087
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.

Operator Surrogate Amount Handled by Operator Amount Collected on Outside Filters (escape) (µg)
1 Lactose 100 g <0.002
DCM 250 mL <10
2 Lactose 100 g <0.002
DCM 250 mL <10
3 Lactose 100 g <0.002
DCM 250 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).

Operator Powder Concentration Inside (STE) Max Outside (STE) (µg/m3) Concentration Inside (TWA) Max Outside (TWA) (µg/m3)
1 Lactose 5.64 (µg/m3) ND 0.38 (µg/m3) ND
DCM 61.90 ppm ND 4.12 ppm ND
2 Lactose 5.64(µg/m3) ND 0.31 (µg/m3) ND
DCM 55.29 ppm ND 3.00 ppm ND
3 Lactose 5.64 (µg/m3) ND 0.33 (µg/m3) ND
DCM 50.20 ppm ND 2.93 ppm ND
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 Tested Total Number of Samples Breathing Zone Samples Area Samples
Total Number Number With Detectable Quantities Total Number Number With Detectable Quantities
Lactose 23 6 0 12 0
DCM 4 3 0 1 0

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


  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 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.

Summary, Containment Testing of Saf T Flow Chemical Fume Hoods

Director of Product and Technology Development

Robert K Haugen  currently designs chemical laboratory containment equipment and develops new relevant technologies for Flow Sciences 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.

Over a period of time ranging from 11/6/2013 onward, the range of standard Saf T Flow Fume Hoods shown below were tested by Flow Sciences using the ASHRAE 110-1995 methodology.  Details of the individual tests are available separately from Flow Sciences; total results are summarized below:

ASHRAE 110-2016 Saf T Flow Test Data Summarized by Volumetrics, Hood Description, and Catalog #:

Procedures and Equipment:

In each test position, face velocities were established using a TSI thermal anemometer and a velocity grid specified in section 6.2 of the ASHRAE 110 standard.

The ASHRAE 110-2016 test procedure used employs a sulfur hexafluoride diffuser set at 30 PSI with a diffusion rate of 4 lpm. Tests were run with the mannequin in place for 5 minutes and SF6concentrations in the mannequin-breathing zone recorded.

An SME (sash movement effect) test was run for a total of two minutes and included opening and closing the vertical sash twice in 30-second intervals over the two minute run. Tests were run with the mannequin in place and SF6 concentrations in the mannequin-breathing zone recorded.

Relevant illustrations from the standard are shown below:

Approved ASHRAE Standard 110-2016 used as an overarching methodology

Ejector Assembly Used in ASHRAE110 and Human as Mannequin Tests


In each test position, face velocities were established using a TSI thermal anemometer and a velocity grid specified in section 6.2 of the standard.

The ASHRAE 110-2016 test procedure used employs a sulfur hexafluoride diffuser set at 30 PSI with a diffusion rate of 4 lpm. Tests were run with the mannequin in place for 5 minutes and SF6concentrations in the mannequin breathing zone recorded.

An SME (sash movement effect) test was run for a total of two minutes and included opening and closing the vertical sash twice in 30 second intervals over the two minute run.  Tests were run with the mannequin in place for and SF6 concentrations in the mannequin breathing zone recorded.

Relevant illustrations from the standard are shown below:

The HAM Containment Test


While comprehensive dynamic tests are not a part of ANSI/ASHRAE 110-1995, it is evident that the low face velocity fume hood vulnerabilities might go unmeasured unless kinetic challenges are systematically introduced into our Safe-T Flow evaluation program.

The researchers decided to “borrow” a kinetic challenge test rather than design a hood to pass the lone and rather perfunctory dynamic sash movement test (SME Test) already in the ASHRAE 110 standard.

The Human as Mannequin Test

Funded jointly by Lawrence Berkeley National Laboratory and the California Energy Commission in 2005, the ECT group investigated kinetic challenges to low velocity fume hoods by developing a special test that used a human with an air sampler in front of a fume hood manipulating equipment in a specifically defined manner.

For this adapted version of the HAM test, the researchers placed a breathing zone monitor on a tripod stand so it and the analysis equipment would not be jarred by the moving operator.  Final array is shown below in Photo #1.  The HAM tests involve conducting a series of choreographed activities using objects located within the hood. The objects consist of two 100 ml measuring cups, a 100 ml scoop, and a spatula.

The modified timed sequence of activities follows the layout shown in Photo # 1

  1. Stand at hood opening with arms to side.
  2. Insert and remove hands and arms
  3. Move objects #1 through #4 from six inch line to twelve inch line
  4. Exchange position of objects. (1 to 2, 2 to 3, 3 to 4, and 4 to 1)
  5. Transfer liquid from scoop #1 to scoop #2.
  6. Place spatula in empty cup.

Each sequence of activities is conducted over a period of approximately 70 seconds


All Flow Sciences Saf T Flow fume hoods pass ASHRAE 110-1995, using criteria set forth in ANSI/AIHA Z 9.5, Section 6.3.7.  A containment level of 0.050 PPM must be achieved in each test to pass, using the pass-fail level of 0.050 PPM established in AIHA Z 9.5; all data from all tests are much lower than this!

ASHRAE 110-2016 Saf T Flow Test Data Summarized by Volumetrics, Hood Description, and Catalog #:

Photos of Hoods under Test

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… 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,, 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.
  4. The Fume Hood Product Life Cycle, A Cost of Ownership Analysis, Haugen, 2018,
  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 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
  3. Necessity is the Mother of Innovation, Haugen


Director of Product and Technology Development

Robert K Haugen  currently designs chemical laboratory containment equipment and develops new relevant technologies for Flow Sciences 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


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.


Contact Flow Sciences

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


Contact Flow Sciences

The Fume Hood Product Life Cycle

The Fume Hood Product Life Cycle

A Cost of Ownership Analysis

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

Flow Sciences, Inc. 

2025 Mercantile Drive

Leland, North Carolina 28451

V 3. 6; 10/31/2017


Flow Sciences manufactures an impressive array of containment products, including fume hoods.


Many lab-oriented businesses purchase fume hoods, including QC labs, hospitals, pharma production facilities, universities, and R&D centers.


In the present economy, project cost and scope are two of the most important parameters to manage. There is substantial pressure on building contractors to pursue the least expensive laboratory equipment solutions to maintain cost controls. This includes chemical fume hoods. Flow Sciences believes this to be an undesirable and cost inefficient strategy as continued customer benefit will decrease during the product life cycle of the fume hood.


Savings on inexpensive fume hoods at the outset of a lab’s operational lifetime are rapidly and inevitably nullified due to persisting and, at times, overwhelming energy costs.


To avoid this situation, fume hood cost of ownership must be defined and quantified to maximize purchasing, construction plans, and continued customer satisfaction based on product performance.


This paper addresses one approach to such an assessment.


Tracking Methods for Lab Exhaust Expenses Over The Fume Hood Product Life Cycle


Flow Sciences worked with Wave Consulting of Wilmington, North Carolina to develop a numerical and economic model that tracked lab exhaust expenses.  Data were collected. Eleven data sheets were used in all, each one comparing the Flow Sciences fume hood with the least energy efficient and least expensive fume hood we could find:

Data Collection and Analysis: Seven Principles


  • Capital Purchase Cost – simply the purchase and installation cost of a new exhaust hood. Many times, this is the only variable evaluated in a purchasing decision.
  • Energy cost defined – the elephant in the room. Fume hoods have exhaust costs conservatively estimated at $10.00 per CFM per year!  Fume hood exhaust CFM is an air stream which carries fumes out of the building. For a surprisingly large quantity of hoods, operation is continuous at 24/7. This air stream is blown into the outside environment and added to the entropy and toxicity of the universe without any benefit except as a fume transport agent. This ENERGY COST is principally derived from fuel cost needed to expel the exhaust air and condition “new” air that replaces it. Most energy sources used today by utilities carry with them huge adverse sustainability issues.


  • Maintenance cost defined

a) Repair – Counterweight cable repair, sash adjustments, cleaning, work top repair, moving the hood to another location. Some hoods with multiple sashes and complicated electronic systems have much higher maintenance costs than other hood systems.

b) Part Replacement – Such parts include VAV retrofitting, cable replacement, baffle replacement, baffle actuator replacement, and counter tops.


  • Selecting Brands of Fume Hoods for Comparison

Flow Sciences specifically analyzed eleven brands of six-foot-wide fume hoods whose exhaust performance data are published by their manufacturers. Each spread sheet compared one of the ten hoods with the least economical hood based on manufacturers published data.


  • Finding Objective Cost Data for Various Brands

We used GSA data and other information to estimate purchase/installation costs and the manufacturers’ self-published exhaust data to estimate exhaust energy costs.  Maintenance costs for each hood were calculated using the author’s own experience with each brand and the complexity of each brand’s design.


  • This Study is a Snapshot

It should be noted that most companies building fume containment equipment are always experimenting with new products and new applications.  Any manufacturer may refine exhaust products and revise downward published exhaust values at any time.  The researcher did not include unpublished data in the analysis presented here.  As improved exhaust products reach the marketplace, we believe the general costing model used here can be extended to these upcoming products.


  • VAV Savings and Replacement Costs were both excluded from this study.

The author realizes that energy savings can be increased by VAV (variable volume fume hoods).

VAV savings are very real; a great deal of work and product research has gone into reducing exhaust volume using such technology. No VAV comparisons are included here because the complexity of such comparisons is beyond the scope of this paper. If VAV fume hood technology is added to the simpler technologies evaluated here, even greater strides toward savings and sustainability will be made.


Also, over an extended number of years, replacement costs may be significant.  Replacement costs for entire fume hoods were not considered here, since the study only investigated savings and costs over fifteen years, a time too short to justify consideration of replacements.

Observations When Comparing Costs of Ownership:                                                                               

The data and model projections covering the ten products mentioned earlier are listed below:

In Table 1, Flow Sciences has added several chart columns to illustrate savings projections:

  1. Yearly cost of ownership takes the 15-year total cost of ownership and divides it by 15. This term is primarily energy expense, but also contains the initial hood cost plus maintenance expenses averaged out over 15 years.  The three most cost-efficient hoods (Flow Sciences, A, and B) measured by COO are the ones at the top of the chart and cost an average of $5,700 per year to own and operate.
  2. Payback Period ranges from “0.51 years” to ”9.7 years” and is the time in years needed for legacy accumulated cost of ownership to exceed accumulated cost of ownership of the fume hood being evaluated. (See relationship 3 below)
  3. Bonus after Payback is the money saved after recovering the purchase price of the fume hood due to energy and maintenance savings.


These data from Table 1 reveal at least five key relationships:

When placed on the same graph with the same scale, differences in installed costs between these hoods appear minor compared to overall cost of ownership. “Energy costs”, roughly proportional to exhaust CFM, IS the elephant in the room.

Any hood that incorporates improved engineering and research to increase efficiency will cost more on the front end.  This initial cost is rapidly recovered over four to eight months, largely with energy savings produced by successfully engineered containment at lower exhaust volume. These savings continue to accumulate for the next 14 years!  Spend this money on any future project you value; this will be a far better investment than throwing dollars up the exhaust stack!

The graph above shows cumulative cost of ownership (CCO) of a typical High Efficiency Hood (Installed cost of $11050) vs. CCO for a legacy fume hood with an installed cost of $8,500 and higher exhaust CFM.  In this extreme example, the HE hood starts showing efficiency paybacks after about FIVE MONTHS.  Other hood-to-hood comparisons in this study show a payback period never greater than 0.8 years for any HE hood compared to a legacy hood.


Who would NOT opt for the HE philosophy when it has such a short payback time!

Relationship 4; Sustainability:


The above data show that a relatively small investment in extra energy-saving and maintenance features produce immediate overall fume hood savings and very short payback. Even though these results are defined within a 15 year “product lifetime”, the most sustainably designed hoods pay off their energy-saving features in less than one year.


While all costs in this study are important contributors to cost of ownership, energy consumption is of overriding importance in assessing cost of ownership.  A more expensive sustainable fume hood is always the better deal, even during the first year of operation!


Using data in Table 1 and conversions readily available7, about $92,670 extra money would be spent over 15 years to run a legacy fume hood rather than an energy efficient one.  At $41.14 per ton, that’s 2252 more tons of coal required over this time period to operate a 6’ legacy fume hood.  However, coal fired power plants are on the average 33% efficient, so that raises the actual coal tonnage to 6824.  When burned, 6824 tons of coal will more or less make 19617 tons of carbon dioxide.  Running through all the conversions, this means a legacy 1050 CFM fume hood will make 1.8 CFM MORE of carbon dioxide pollutant compared to a high efficiency hood.  This means such a hood has a (100*1.8/1050) or a 0.17% exhaust volume tax of CO2 as a result of the coal being burned to operate the hood.  If this CO2 stream were added to the hood’s exhaust (instead of being given off at an electrical plant), it would boost the exhaust contaminant CO2 concentration by 1700 PPM at the fume hood exhaust stack.


Relationship 5, Due Diligence:


All high efficiency fume hoods are NOT created equal! This white paper is based only on measured exhaust volume and resulting costs. Our own research shows careful testing must prove good containment occurs at the lower design exhaust volume used by high efficiency hoods. In the real world, superficially “minor” hood characteristics can cause major problems with containment. Check these two preliminary “Sash Movement Tests” (ASHRAE 110-2016, Section 8.3) on a developmental Saf T Flow high efficiency fume hood run at 60 FPM:

Just altering the sash handle depth 1 ¼ inches improved the containment from marginal to superior under dynamic challenge!  These types of variance in prototype HE hoods performance means A  candidate high efficiency fume hood must have been validated using reproducible 3rd party ASHRAE 110 containment data under the proposed operating face velocity and make-up air conditions!




In summary, the author believes there are four indisputable reasons to select a high-efficiency hood over a legacy hood for whatever laboratory application presents itself:


  • High efficiency fume hoods like the Saf T Flow hood save money on energy, repairs, and down-time over a legacy hood, even within the first year. In this first year, the added purchase cost of a high efficiency unit is overwhelmed by the savings in cost of ownership. (Relationship #3)


  • Whether cheap or expensive, all hoods have a purchase/installation price powers of ten lower than the 15-year energy cost to support them.


  • Legacy fume hoods have adverse impacts of carbon dioxide production and wasted energy. High efficiency fume hoods have a very large potential to support sustainability related to these expenses.


  • All high efficiency hoods are not created equal. In all cases, a series of standardized containment tests should be performed with good results as a final necessary guarantor of the selected high efficiency fume hood.


Contact Flow Sciences


VAV Energy Savings at High and Low Fume Hood Face Velocities

VAV Energy Savings at High and Low Fume Hood Face Velocities

Robert K. Haugen, Ph.D.

       Director of Product and Technology Development

      Flow Sciences, Inc.


I. VAV (Variable Air Volume) Fume Hoods Defined:

According to Northwestern University Office for Research Safety1, variable air volume fume hoods are:

(Fume hoods that) maintain a constant face velocity regardless of sash position. To ensure accurate control of the average face velocity, VAV hoods incorporate a closed loop control system. The system continuously measures and adjusts the amount of air being exhausted to maintain the required average face velocity. The addition of the VAV fume hood control system significantly increases the hood’s ability to protect against exposure to chemical vapors or other contaminants. Many VAV hoods are also equipped with visual and audible alarms and gauges to notify the laboratory worker of hood malfunction or insufficient face velocity.

It is also true that as VAV hoods reduce exhaust volume, they can significantly increase the energy efficiency and sustainability of the lab exhaust operation. 2

We will focus on fume hood exhaust CFM in this paper.  An architectural approximation $10 per CFM per year (fan use, air conditioning energy, and heating expense) will be used to estimate this exhaust expense over time.

II.VAV Savings using a face velocity of 100 FPM:

What follows is a comparison of exhaust volume and energy savings using a 6’ classical constant volume fume hood and the same hood using VAV controls:

A. Constant Volume Math:

Using a constant volume 72” wide fume hood running at 100 FPM @ 28”high sash opening for one day:

24 Hours X 60 min/hour X 1245 CFM catalog exhaust volume = 1.8 Million Cubic Feet per day exhausted

B. Variable Air Volume Math:

A VAV hood reduces volume as sash is lowered to maintain a constant face velocity above a minimum air change rate, which we will assume for this exercise is 5 air changes / minute, or 300 air changes per hour.  Generally speaking, such a number is regarded as safe to prevent explosions and interior hood corrosion. 3

  1. At full open & 100FPM, hood will exhaust 8 million Cubic feet per day, just like the constant volume hood reviewed above.
  2. At 18” & 100 FPM, hood will exhaust this calculated reduced air volume:

((21.5” X 62.5”) / 144 sq.”) X 100 = 933 CFM = 933 CFM, or 1.3 Million Cubic Feet per day exhausted

     Note: Very First term includes 18” sash opening plus 3.5” of airfoil and bypass opening

  1. At completely closed, hood will only exhaust:

((3.5 X 62.5)/144) X 100 =152 CFM= 0.22 Million Cubic Feet per day (CFD) exhausted

  1. Here’s where calculating VAV exhaust and energy savings becomes imprecise. Will lab personnel keep the sash down, operate at 18” sash opening, or operate at full open sash? We cannot compute effectiveness of VAV without knowing the answer to this question. For the sake of argument let’s assume the average sash position is the mathematical average of the three numbers calculated above: (1.8 + 1.3 + 0.22)/3 = 1.1 Million CFD:

1.8M -1.1M =700,000 CFD savings or 478 CFM average savings. At $10 per cfm per year, this is annually $4780/year savings on one hood.

Can VAV Save Money?

A 72” VAV fume hood can therefore generate average annual savings of ~ $4780 per year, however, such savings require not overtaxing the make-up air machinery designed to “feed” this system!

What’s The Caveat Emptor?

A reduced volume exhaust system has several “gambles” built into it based upon assumptions about human behavior! If the researchers do not close the VAV sashes or behave improperly in other ways, far less energy will be saved than the calculations predict.

If building designers downsized HVAC make-up air based on aggressive VAV assumptions, the building may not be able to heat or cool itself properly when temperature conditions are very hot or very cold and fume hoods are simultaneously wastefully run with sashes full open. If behavior does not match expectations, the building may not be able to maintain intended thermostatic conditions.

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III. VAV Savings using a face velocity of 40 FPM:

Mechanical engineers might consider additional measures to augment VAV savings when designing a fume hood exhaust system.  Two likely targets in the hunt for savings are face velocity and maximum operating sash position. We have recently seen several large jobs where the VAV face velocity is specified not at 100 FPM, but at 40 FPM with a max. sash position of 18”, not 28”. Let’s see mathematically what happens at this reduced face velocity and sash opening to VAV savings:

A. Constant Volume Math:

Using a constant volume hood running at 40 FPM and18” sash opening for one day:

24H X 60 min/hour X 374 CFM = 539,000 Cubic Feet per day exhausted. Notice that the original constant volume annual cost calculated at 100 FPM and a 28” open sash was 1,800,000 Cubic Feet per day exhausted.  We instantly save 1.26 million Cubic feet of exhaust per day, before we even add VAV!

B. Variable Air Volume Math:

A VAV hood reduces volume as sash is lowered to maintain a constant face velocity above a minimum hood cavity air change rate, which we will assume for this exercise is 5 air changes / minute, or 300 air changes per hour.  Generally speaking, such a number is regarded as safe 3 to prevent explosions and interior hood corrosion.

  • At 18” & 40FPM, hood will exhaust 374 CFM or 539,000 Cubic feet per day, just like the Constant volume hood reviewed above.
  • The minimum 300 air changes per hour is 300 X (62.5 X 24 X 48)/1728 = 12,500 cubic feet per hour = 300,000 Cubic feet per day
  • Average low and high cubic feet per day to obtain average total daily cubic feet.(539,000+300,000)/2 = Average volume exhausted using VAV= 419,500 CFD
  • Savings is difference between line 1 and line 3 = 539,000 – 419,500 = 119,500 CFD
  • This 82.9 CFM average reduction is about $829/year in energy savings.

These parallel calculations of energy savings make a serious point: The lower the baseline acceptable face velocity and maximum sash position are, the greater the energy savings is BEFORE we consider VAV’s contribution. As the third technology (after face velocity and sash position), VAV still saves energy, but dramatically less than when it is considered the first technology.

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IV. Preventing Dangerously Low Air Changes within the Fume Hood Cavity

Let me cite an experience from a very early VAV system I checked out in 1984.  This customer was dissolving small samples of limestone in dilute hydrochloric acid (HCl) on hotplates inside a VAV fume hood with the sash closed.

The hood interior environment became hostile and corrosive. The hotplates corroded. The stainless steel sash frames corroded on the interior-facing side. The customer called us in to “fix” the hood.

The first-gen VAV installed in this lab hood ramped exhaust down so face velocity was always 100 FPM, right down to full sash closure. Velocity checked out at 100 FPM all the way down.  The problem was, at full closure and no bypass, the only air route into the hood was the 1” slot under the airfoil.

A.    On this 6’ hood, this meant exhaust volume was

CFM = (1” * 62”/144 sq. inches per sq. foot )*100 FPM = 43 CFM.

B.    Hood internal volume was Vol = 48” * 62” * 22” / 1728 cu inches per cu foot = 37.9 Cu Ft

C.   Internal Air changes were therefore ACM = 43/37.9 = 1.13 ACM, or 1.13 * 60 = 68 ACH

All the corrosive issues appeared to be caused by LOW AIR CHANGES at full sash closure. We experimentally proved this on site. At the time I did this research, I discovered corrosion in this application stopped happening if minimum airflow was increased to about 5 ACM (300 ACH). Other engineers were noticing similar issues. Over time, air change rates themselves became controversial to the extent that now a “suggested range” of 150 to 375 ACH is cited in ANSI/AIHA Z9.5 – 2012 3. Other researchers also note theoretically a danger of explosive vapors building up at air change rates lower than the range set forth in Z9.5.


Most VAV manufacturers now allow the inclusion of a minimum air change rate into the VAV algorithm defining exhaust demand at all sash settings. For a representation of this new controller function, note the contrast between the two lines on the chart below where blue line represents a VAV unit where face velocity is constant down to sash closure and orange line represents exhaust reduction only down to minimum air change rate:



Notice how much one must limit the air savings VAV achieves to get our 300 ACH minimum.  The last nine inches of sash travel earns not one extra CFM of energy savings on the orange line.

Check out the next graph!  Many designers now wish to lower the sash upper limit to 18” rather than 28”. This limits maximum CFM as one raises the sash and also allows most hoods to pass ASHRAE 110 containment since the sash rail at 18” remains below the average operator’s breathing zone during all procedures. In this VAV approach, it is not recommended to use the sash during an active experiment above 18”.

Same shape, right?  What’s the big deal?


Notice that the VAV system now only modulates airflow (orange line) over 8” of sash travel from 18” down to 10”!  Again, as we reduce maximum sash opening and increase minimum air changes, the operational influence of VAV on fume hood exhaust becomes less and less.

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  1. A variety of different methods for reducing fume hood exhaust volume exist. VAV fume hoods are a prominently mentioned method of saving exhaust CFM and gaining significant financial and environmental benefits. An example used in this paper demonstrates large savings using a VAV hood operating at 100 FPM and 28” sash opening.
  2. As other, simpler, modifications are made to fume hood applications, it becomes apparent much of the savings these methods achieve are the same dollars saved by VAV that were discussed in conclusion one.
  3. VAV technology requires careful consideration of what happens if fume hood interior air changes drop too low. There is no agreement in the literature about where this air change magic number exactly lies.3 It very well may be inside the range AIHA Z9.5 cites between 150 and 375 ACH, but exactly where? The “right” minimum air change rate also depends on the challenge rate of fumes introduced into the hood, which obviously depends on the process/application being undertaken. We shouldn’t guess at this number! The most current ACH reference of 150 to 375 has a range of 250%! In my opinion this is like posting a speed limit sign of 50 to 125 MPH!  Safety assessment of the minimum air change rate should be application-specific and empirically tested with fume hoods that are on site.
  4. In this limited study, it appears much of the calculated energy savings attributed to VAV may be achieved by alternate means. If our architectural design objective is to run an energy-efficient lab that is also safe, we should focus on the best mix of many available technologies. Another paper in this series, Low Hanging Fruit 5, focuses on seven widely used strategies, picking the least expensive alternates first.
  5. Finally, all hoods are not created equal.4 Some high efficiency hoods may require a lower minimum air change rate than others! Do we decide to pick the “safest” hood regardless of price, or the least expensive system with the highest ROI? The facilities planner and scientist have already lost if they believe such a choice is valid or necessary. Picking a fume hood that contains well at lower velocities and selecting energy savings objectives that match the applications being used in the lab in question are both possible in the same assessment and should be unwaveringly advocated.
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3.      ANSI/AIHA Z9.5 – 2012 p 25 cites a range of 150 to 375 Air changes per hour as been used to control vapors inside fume hoods
4.      Side-by-Side Evaluation of High Performance Fume Hoods for the University of Texas, Kevin Fox and Bernard Bhati, Labs 21, 2008


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Fume Hood Energy Savings - Low Hanging Fruit

Fume Hood Energy Savings – Low Hanging Fruit

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

Flow Sciences

2025 Mercantile Drive

Leland, North Carolina 28451

Low Hanging Fruit

In this era of energy conservation and sustainability in new lab construction, one economic question stands above all others:

“With so many fume hood energy-saving exhaust options available, which options are the most significant?”

There are many candidates. Variable Air Volume Exhaust companies claim 63% to 80% savings if new lab facilities employ VAV.1, 2, 3 Fume Hood manufacturers claim new “low volume” exhaust hoods can save over 60% of energy.4 Companies that manufacture self-closing sashes claim their devices can save 60% of energy in conjunction with VAV. 9

Other technologies exist, such as exhaust heat reclamation, nighttime setback, weekend setback, etc. Representatives of each of these technologies all have energy savings claims, but why even consider any of these, since the technologies specifically mentioned above have already saved around 200% of our current energy use!


Obviously, something is wrong here. We can never save all the HVAC and fan power costs involved in running a laboratory exhaust system since the savings for technologies mentioned above are all interrelated! In addition, each technology has associated first costs that need consideration.

Consider the following chart that lists approximate cost savings of 20, 6’ fume hoods in a facility. The chart ignores, for the time being, interrelationships between various strategies. The author uses trade knowledge and published claims for each of these costs, realizing that approximations are involved:

To make better sense of these data, we must never “double-count” savings by technologies that share similar approaches. We need to serially apply these technologies in the same order listed above (cheapest options first; here is where “low hanging fruit” comes in), and show the “chunk” of energy saved successively in each step. In this way, we will get an idea about how to proceed with the true economies of each technology. What follows is a chart that does exactly this:

Attached below are two charts describing aspects of the data:

Some “Conclusions”:


  • The ORDER in which energy saving options are applied is critical. The expenses associated with each strategy differ widely. Claims made by advocates of each strategy need to be carefully analyzed as part of the entire energy saving package. Most importantly, employment patterns and the hourly staffing needs of the research facility should be used to frame the context in which low-hanging fruit options should be evaluated. If taken in reverse order of cost, the best bang for the buck is springing for a more expensive high efficiency fume hood, which results in the ability to dramatically lower face velocities.


  • The first three basic low-tech and lower cost energy conservation steps, when applied before other technologies, result in cutting energy spent exhausting fume hoods by so much (68.0%), that the remaining four higher-cost conservation methods make relatively minor contributions (11.1%). These last four technologies cost $252,000, compared to the first three costing NEGATIVE $2,600 (since we save money by buying smaller five-foot hoods).
  • By no means does conclusion #2 mean VAV is a bad investment. It’s just not the best investment. Smaller hoods, or a reduced number of hoods, may not be options in all cases. Safety representatives may wish to require hoods to operate at any sash position, regardless of what effect this has on potential energy savings. It also may not be acceptable by state and/or corporate standards to run hoods at an 18” sash height and 60 FPM. These factors may require VAV be used as a principal conservation strategy, which will increase its proportional importance.
  • What the above study does unquestionably show is that low-cost, acceptable energy reduction strategies (low hanging fruit) should be considered first.  The above study did not even include other possible low fruit strategies; for example:


  • Allow hoods not in use to be switched off entirely.
  • Use air from adjacent office areas to be part of the make-up air for lab areas.
  • Target research hours for “off peak load” times.
  • Tolerate higher room temperatures in summer and lower temperatures in winter.
  • A word about lab design: how people work and what they are doing are inescapably important in how modern buildings conserve energy.

Have lab planners asked important questions about what research behavior will be practiced in a new building?

  • Is the lab designed to function 24/7? 8/5? Unpredictably?
  • Is facility to be multi-shift?
  • Is building located in an urban or rural setting?
  • Are wind or solar options available?
  • Does the facility occupant have the option to schedule work hours to reduce energy costs?


  1. 80% reduction predicted by Siemens Doc # 149-976, 2003. A width reduction on interior opening width for Saf T Flow hoods used in analysis is 62.5” down to 50.5, or a reduction of volume multiplier of 0.808.
  2. 63% reduction claimed by Lab Design News, Ronald Blanchand,10/15/2013; in this study, original 5’ 100 FPM volume is 983 CFM, which is reduced to 590 CFM at 60 FPM. Multiplier of remaining volume is 0.6.
  3. 75% reduction claimed by Newtech at:
  4. 60% reduction claimed by Flow Sciences Catalog, pp 98, 99, 2014
  5. Costs estimated for 20 fume hoods in temperate climate. This first chart ranks savings strategies from least costly to most costly.
  6. Installed Cost
  7. Cost added for low constant volume, high efficiency fume hood
  8. Auto close sash saves no money unless coupled with VAV. Since 60 FPM already in force, VAV savings are based on a greatly reduced volumetric base number required to achieve 69 FPM with closed sash..

Methods of Calculating Quantities in Table 2: Note percent savings is always calculated using ORIGINAL energy cost in the denominator.  

  1. Smaller hood energy savings:  In this example, going from a 6’ hood to a 5’ hood.

Energy savings is equal to volume of exhaust. At comparable sash heights, ratio of 5’ sash width to 6’ sash width times 100 will be % of volume exhaust a 5’ hood has compared to a 6’ hood. Using the Flow Sciences standard fume hood, ratio is as follows: R = 100 * 50.47”/ 62.52” = 83%; (17.0% savings)  

  1. Reduce Face Velocity: When face velocity is reduced from 100 FPM to 60 FPM, a 40% reduction of remaining exhaust volume is saved:

        R = 100 * 60 FPM/ 100 FPM = 60%; (33.2% savings)    

  1. Sash stop at 18”: 18/28

Full open sash = 28”; ratio of volume at 18” is (17.8% savings)

  1. Weekend setback to 40FPM at 18”

(previous total – (2/7)*2/3 * energy cost) = (3.1% Savings)

  1. Weekday night time setback based on 14 ours at 40 FPM per week night = (4.4% savings)
  2. Exhaust heat/AC reuse extract (0.1% savings)
  3. VAV and auto sash

Assume average savings of 87 CFM since velocities and other factors already accounted for; (3.5% savings)


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