Fume Hood Protocol Comparisons

Overview of Evaluation Protocols

ASHRAE
Currently, the most commonly requested fume hood evaluation protocol is the ASHRAE 110 method. ASHRAE is the American Society of Heating, Refrigeration and Air-conditioning Engineers. ASHRAE is a non regulatory, profit making organization. Although it publishes "standards" none of the standards are binding on U.S. businesses. The ASHRAE 110 standard is an excellent procedure and, in my opinion, achieves its stated goal.

The ASHRAE protocol is a rather complicated three parted evaluation processes which includes placing a gas detector in a mannequin's mouth in front of the hood and injecting a tracer gas into the hood. Although the most elaborate and certainly the only national consensus quantitative evaluation proposed by a U.S. organization, this method is not considered to be capable of ensuring optimal performance of the hood in an "as used" fashion (even by ASHRAE itself).

However, there are considerable misconceptions regarding the ASHRAE standard. It was not an attempt to provide what would constitute a performance criteria, but rather, an attempt to standardize the way in which hoods could be evaluated. Essentially the ASHRAE standard is based on a test procedure designed by K.J. Caplan and G.W. Knutson and published in the Journal of the American Industrial Hygiene Association in 1982. Contrary to common belief, the standard does not make specifications as to what is considered to be acceptable and an hood cannot be “certified” according to the ASHRAE standard.

The ASHRAE 110-1995 is not an engineering investigation into what causes poor performance, nor of ways to improve performance. Indeed, the standard is not even capable of identifying where within the hood the worst performance is exhibited.

The ASHRAE protocol requires elaborate (and expensive) equipment; purpose built tracer gas ejectors, electron capture instrumentation, and mannequins. In the following protocol, the inspector takes the place of the mannequin and the human experience takes the place of the electron capture instrumentation. This change alone results in a reduction of initial costs and rental fees. The down-side to the protocol, is that the protocol is subjective, but no less subjective than the ASHRAE fume challenge.

To my knowledge, where an organization has the equipment necessary for the ASHRAE protocol, that equipment has been “home-made” by that organization. Some years ago, I contacted the original researcher who developed the method and designed the original test equipment (Mr. Knowlton Caplan), and at the time, he was not aware of anyone in the country who manufactured, sold or rented the necessary equipment.

The ASHRAE protocol necessarily requires set-up time to place the test apparatus in place. In this protocol, the set-up time is complete when the inspector steps up to the hood.

It has been my experience, that where fume hoods fail, they fail grossly. The failure is usually sufficient to be detected by a carefully conducted visual fume test. The ASHRAE fume test, however, is NOT a detailed challenge; checking only the perimeter of an hood interior. Therefore, the ASHRAE 110-1995 fume test is incapable of identifying even a grossly inadequate hood where the reversal is in the central portion of the hood face. I have seen many hoods which can "pass" an ASHRAE fume test, but will utterly fail to protect the hood user. It is for this reason, that when the ASHRAE test is used, the hood owner should follow the ENTIRE ASHRAE test and not just the visualization fume challenge.

Although the ASHRAE test quantifies the amount by which the fume hood fails, I believe that under most laboratory situations, it is not necessary to determine the actual amount of failure but rather to document that the hood has failed and attempt to ascertain why.

AIHA
Jointly published by the AIHA and ANSI, Standard Z9.5-2003 is an American National Standard for Laboratory Ventilation. The AIHA standard is not binding on US industry.

SAMA
SEFA and SAMA are furniture and apparatus manufacturer associations. As with ASHRAE, their protocols are not binding, and are not recognized by NIOSH, the EPA, OSHA or other regulatory agencies. They are instead an attempt to share with the general community their experience in fume hood performance in the spirit of disseminating information. In fact, SEFA and SAMA never sought to copyright their protocol and allows anyone to photocopy or quote the material without restriction.

The SAMA LF10 protocol was originally developed incorporating considerable technical input provided by SEFA. In 1988, SEFA separated from SAMA and SAMA separated itself from fume hood evaluations. SEFA took up the task of keeping the protocol current. The SEFA-1 protocol supersedes the old SAMA LF10 protocol. Indeed, if one were to attempt to obtain a copy of SAMA LF10 from SAMA, SAMA would recommend calling SEFA, since SAMA has since disposed of all SAMA LF10 copies. There is no significant difference between the SAMA and SEFA field testing protocol.

It is generally recognized by most researchers and industrial hygienists involved with fume hoods, that the SEFA and SAMA protocol are not adequate to determine the ability of the fume hood to protect the worker. Although the new SEFA-1 does address field testing of fume hoods, it is primarily a design protocol. The SEFA protocol contains several inconsistencies. For example, the evacutory volume (Q) is determined from face velocities, yet the supply Q is determined by drilling holes in the supply duct and measuring dynamic pressure even though measuring the velocities of the supply would be much faster (only seconds) and non-destructive. Additionally, the SEFA protocol suggests disengaging the auxiliary air while measuring the face velocities. I believe that since the auxiliary air will be on when the hood is used and the auxiliary will effect the face velocities, the auxiliary air should be operating in its normal fashion.

I have encountered specifications which require hoods to be certified according to the SAMA LF-10 "Standard." The SAMA protocol is not a standard and has no certification criteria; that is to say that there is no such thing as a SAMA certification; thus, hoods cannot be certified according to SAMA. Additionally, some specifications require that hoods be balanced according to the SAMA protocol. The SAMA protocol does not address balancing of a fume hood.

US Regulators
The Occupational Safety and Health Administration (OSHA), and the US Environmental Protection Agency (EPA) do not have regulatory standards for the performance of laboratory fume hoods. However, OSHA and the EPA both have addressed fume hoods, and more information can be found by clicking here.

The Centers for Disease Control/NIOSH pamphlet entitled "Biosafety In Microbiological And Biomedical Laboratories" does not provide performance criteria for control devices.

NSF
The NSF has several standards which describe many aspects of biological safety cabinets. NSF 49 is a comprehensive performance standard for biological safety cabinets, but does not address laboratory fume hoods.

Deutsches Institut für Normung
The Deutsches Institut für Normung DIN 12 924 standard entitled "Laboreinrichtungen Anforderungen an Abzüge, Abzüge für allgemeinen Gebrauch" is binding on German industry. The standard is considered state of the art, but does not necessarily reflect the highest standard of care. Additional information on the DIN can be found by clicking here.

British Standard 7258
British Standard DD 191 has been replaced by BS 7258. Again, the standard is state of the art, but does not necessarily reflect the highest standard of care.

National Fire Protection Association, Inc.
NFPA 45- Standard on Fire Protection for Laboratories Using Chemicals (2000 Edition). This standard is an excellent reference for fire protection. However, it also underscores the problems that can occur when an organization whose primary focus is in one arena (such as fire protection) but who attempts to make standards in another arena (such as laboratory ventilation). The result is that poor advice may be given, which tends to lower the quality of the standard as a whole.

General Observations

The evaluation protocol described below was developed following extensive review of studies and guidelines published by (but not limited to) ASHRAE, SEFA, SAMA, EPA, OSHA, School of Public Health, (University of Minnesota), and Oak Ridge National Laboratory (Department of Energy) and numerous articles in the scientific literature. In addition to these various organizations, I have incorporated my personal experience of over 25 years working in and around analytical and research laboratories with chemical fume hoods.

The protocol I use in my private consulting business (Forensic Applications Consulting Technologies, Inc. FACTs) gathers more information than is needed for a performance evaluation; it gathers data regarding the hood’s engineering performance, the state of repair of the hood, and a commentary on work practices. And, like the ASHRAE 110-1995 standard, and the SEFA and SAMA protocols, it uses a subjective performance based test to evaluate air flow characteristics. Unlike the ASHRAE standard, this protocol does not quantify the actual concentration of spill-out. This one item, is the only significant issue which this protocol does not address but that the ASHRAE standard does. Another small item is that the ASHRAE standard requires a sketch of the lab to be made; this protocol does not.

This protocol covers all aspects that are covered in the SEFA and SAMA protocol and, in addition, covers those aspects listed in the following table. Below is a table which compares the issues addressed by the various protocols. Where a "Y" appears in the table, the protocol addresses the issue, where a blank appears, the protocol does not explicitly address the issue.

Evaluation Groundwork
The protocol I use is not a cookbook method. It requires a patient, intelligent and conscientious evaluator. However, in unpublished work, approximately 10 years ago, Mr. Tom Smith, (Exposure Control Technologies, Inc.) and I performed blind ASHRAE –100 comparisons with this protocol. What we found was when diligently performed, this protocol identified each hood that had been found to be substandard by the full ASHRAE 110 method. Similarly, each hood initially identified by this method as deficient was subsequently identified by the ASHRAE 110 method as deficient.

Since, as a private consultant, we live in the real world of marketing and perceptions, the evaluation described here is sensitive to the pressures of marketing and public relations. I am cognizant of the fact that many contracting officers and lab managers simply would not hire a consultant to perform an hood evaluation if the evaluation protocol did not include face velocities. For this reason, the form displays expected albeit occasional, unnecessary information, including face velocities. However, once the full evaluation has been performed, just the “Performance Characteristics” section of the evaluation needs to be conducted to ensure the continued performance of the hood.

Although an IH with no lab experience can certainly use the protocol, the realities are that if the IH doesn’t understand laboratory settings and the work that is taking place therein, the performance test will be limited by his own knowledge. This is because the protocol begins with simply understanding the work that is to be performed in the hood and determining if a laboratory hood is even the most appropriate type of control. If, for example, work involves substances such as bis-choromethyl ether, materials potentially contaminated with bloodborne pathogens or large pieces of equipment, then perhaps a laboratory fume hood is not the correct control device regardless of how well the hood works.

Similarly, if the hood is used to control relatively innocuous substances such as MeOH, acetone, toluene, etc, then a lower performance may be tolerated since even a lower performance may provide adequate protection. The evaluator should be given the ability to ensure that the hood is providing an appropriate level of control.

In general, hoods that pass this protocol may be expected to give a protection factor on the order of 1E5 to 1E6.

Evaluation Form
A standardized form is used to ensure that consistent evaluation of each hood is achieved, and that a record of performance is established. The form contains a large square in the centre depicting a graphic of the face of the hood. The depiction permits the evaluator to note areas of reversal, static zones, face velocities, and disruptive influences (such as large pieces of equipment in the hood).

The form I use to record the performance of each hood supplies more information than is needed to satisfy the objectives of a performance evaluation. The intent is to provide sufficient information to facilitate further investigation in the event that an hood performs poorly.

The complete evaluation, minus the sound criteria, takes approximately 15 minutes per hood. Typically, I carry a small tape recorder and dictate the evaluations onto tape, and later transcribe the information onto the forms. In this fashion, as many as 20 hoods can be evaluated in a single day allowing for time to make minor adjustments.

Hoods normally are evaluated either "as manufactured" or "as used." Obviously the "as used" is the better of the two choices since even the very best and properly designed and built hood may utterly fail if poorly placed within a lab, or the lab employee exhibits poor work practices (such as hanging a lab coat on the utility knobs). Therefore, hoods are evaluated as I find them. Where necessary (such as to lower the sash) I will move equipment, but otherwise the hood is evaluated as it is found.

Face Area: Face area is measured using a standard tape measure. The unit's dimensions are square feet.

By-pass Baffle: During the evaluation, the efficacy of the by-pass baffle is evaluated. During this determination, the hood sash is lowered to an opening of about five and a quarter (5.25) inches, and the face velocity is measured at three equidistant points using an hot wire anemometer. The "mean closed velocities" is the arithmetic mean of nine tenths of the altitude corrected individual readings.

The closed velocities serve to evaluate the effectiveness of the by-pass baffle in the hood. As mentioned earlier, the function of the by-pass is to allow make-up air, circumventing the sash, into the hood as the sash is lowered, thus maintaining a steady-state hood static pressure (SP_h) without creating excessive face velocities. The open-to-closed velocity ratios provide the best measurement of how well the by-pass baffle is working.

In a properly operating by-pass hood, the "closed to open" ratio (C:O) should be no greater than 3 and no less than unity. ² C:O ratios greater than 3 are indicative of a dysfunctional by-pass baffle (or a hood that is a simple cabinet). Hoods displaying C:O ratios greater than 3 should not be used for powders or open flames. A hood with a C:O ratio less than unity may indicate a gross leak somewhere in the casework of the hood.

Evacutory Volume: For most laboratory fume hoods, the manufacturer designs the device to evacuate a specific volume of air (Q) per unit time, per unit face area. For non-specific laboratory fume hoods, the design criteria is incumbent on several parameters which must be evaluated by the manufacturer. ¹ For most hoods, the design criteria for Q is 100 cubic feet of air per minute (cfm) per square foot of maximum open face area.

To ensure that the design criteria has been met, it is often convenient to measure the velocity of the air at the face of the hood, since the velocity of the air at the face will be a function of the face area and Q. Traditionally, too much faith has been placed in the value of face velocities as an indication of hood performance. Face velocities are useful as diagnostic indicators in the event that the hood does not perform well, but should not be used as the sole method for determining the effectiveness of the hood. A discussion on face velocities can be found by clicking here.

Although there are several variations on the theme, by-pass hoods have a variable inlet baffle which permits more air to enter the hood via a special inlet as the sash is lowered. The effect is to maintain a non-linear increase of face velocity as the sash is lowered, to avoid excessive face velocities when the sash is only opened by a foot or so; again the velocities change but the Q remains essentially constant. It is for this reason that the results of the face velocity measurements taken have been calculated as evacutory Q and compared to the evacutory design criteria of the manufacturer. The value of Evacutory Q reported on the form is the product derived from the arithmetic mean of the barometric corrected individual face velocities and the face area.

Face Velocities: Although I believe that traditionally, too much weight has been placed in face velocities, this protocol does measure face velocities. In fact, this protocol more precisely measures the face velocities than does the ASHRAE 110-1995, SAMA and SEFA protocols. In the FACTs protocol, face velocities are measured at one square foot intervals using a 16-point pressure differential grid per square foot. The air velocity is integrated over each sampling area. In this way, hundreds of face velocity measurements are taken across a standard hood face. The velocities are corrected for local altitude and temperature. The instrument calibration is traceable to NIST (formerly the National Bureau of Standards, Department of Commerce).

The sampling points were determined by "drawing" an imaginary equidistant grid in the face of the hood. For a typical laboratory chemical fume hood, the centre of the second or third reading position would roughly be at the nose of a “model man” user, when standing at the face of the hood.