Laboratory Hoods Use and Evaluation

Transcription

1 Laboratory Hoods Use and Evaluation Caoimhín P. Connell Forensic Industrial Hygienist Forensic Applications, Inc. 185 Bounty Hunter Lane Bailey, CO www. Topics of Discussion Regulatory issues and Industry Protocols Hood Classifications Evaluation methods NCAR October 29, 2010 Performance Confounders 1 2 Pertinent Standards and Protocols OHSA NIOSH ANSI/ASHRAE NFPA AIHA ACGIH SAMA SEFA Miscellaneous International Standards German DIN British HSE DD 191 Canadian CSA: Standard Z (Fume Hoods and Associated Exhaust Systems) 3 OSHA Regulations OSHA has extended its authority into the lab industry with 29 CFR ; The "Occupational Exposure to Hazardous Chemicals in Laboratories" standard. This standard places several regulatory burdens on laboratories including the requirement to establish a Chemical Hygiene Plan and a requirement that specific measures are taken to ensure that fume hoods are functioning properly ( (e)(3)(iii)). 4

2 OSHA Although OSHA does specify minimum face velocities for laboratory fume hoods in several compound specific standards (29 CFR ,.1004,.1007 et al), these standards are not applicable to laboratories by virtue of the decision by the United States Court of Appeals for the Third Circuit in Synthetic Organic Chemical Manufacturer's Association v. Brennan, 506 F. 2nd 385 (3d Cir. 1974), certiorari denied 423 U.S (6) Furthermore, in light of the current state-of-the-art information on face velocities, OSHA will consider hoods which are outside the specified minimum face velocities as de minimis violations. EPA Although the U.S. EPA has sponsored several research papers in fume hood evaluation and efficacy, there are no EPA regulations concerning fume hood efficacy which are binding on US industry. 5 6 NIOSH CDC (NIOSH)/NIH The National Institute of Occupational Safety and Health is administered by the Centers for Disease Control, US Department of Health and Human Services. NIOSH may investigate workplace exposures and report to OSHA on any deficiencies which are observed. NIOSH has no hood regulations. The CDC pamphlet titled "BIOSAFETY IN MICROBIOLOGICAL and BIOMEDICAL LABORATORIES" does not provide performance criteria for control devices. 7 8

3 ASHRAE ASHRAE Standard Method of Testing Performance of Laboratory Fume Hoods State-of-the-art National consensus standard The American Society of Heating, Refrigeration and Airconditioning Engineers is a nonregulatory profit making organization. Although it publishes "standards" none of the standards are binding on U.S. businesses per se. Evaluation Protocols ASHRAE The ANSI/ASHRAE method METHOD OF TESTING PERFORMANCE OF LABORATORY FUME HOODS (ISSN ) supersedes the ANSI/ASHRAE This standard is a quantitative evaluation of hood performance But: This standard defines a reproducible method of testing laboratory fume hoods. It does not define safe procedures. The procedure is a performance test method and does not constitute a performance specification. It is analogous to a method of chemical analysis, which prescribes how to analyze for a chemical constituent, not how much of that substance should be present. Another analogy would be a method for measuring airflow; it prescribes how the flow should be measured, not how much it should be ASHRAE 110 Protocol The method consists of three parts: 1) Flow visualization 2) Face velocity measurements 3) Tracer gas containment evaluation The ANSI/ASHRAE method is currently the national consensus standard for hood performance. However, the authors of the standard were astute enough to recognize that the standard is not a catch-all and the results of the evaluation must be considered by an individual well versed in fume hood use and performance. 11 ASHRAE 110 Protocol The method consists of three parts: 1) Flow visualization 2) Face velocity measurements 3) Tracer gas containment evaluation The ANSI/ASHRAE method is currently the national consensus standard for hood performance. However, the authors of the standard were astute enough to recognize that the standard is not a catch-all and the results of the evaluation must be considered by an individual well versed in fume hood use and performance. 12

4 ASHRAE Tracer Gas Containment Test HOOD TRACER GAS SAMPLER/ DETECTOR TRACER GAS CLOUD TRACER GAS ANALYZER TRACER Tracer Gas Analyzer TRACER GAS GAS SOURCE MANNEQUIN EJECTOR (SF 6) Hitchings Associates, PC used with kind permission Mannequin & Tracer Gas Detector Hitchings Associates, PC used with kind permission ACGIH The American Conference of Governmental Industrial Hygienists is not regulatory governmental organization. The ACGIH is a private professional organization which, like ASHRAE publishes recommended standards. Some ACGIH standards may be incorporated by reference into federal, state or local codes. Some ACGIH standards may be incorporated by reference into federal, state or local codes ANSI/AIHA ANSI Z (Laboratory Ventilation) ANSI Standard Z (Hazardous workplace chemicals) State of the art National consensus standards 15 16

5 NFPA NFPA Standard on Fire Protection for Laboratories Using Chemicals State of the art National consensus standards SAMA and SEFA 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 organizations. They are instead an attempt to share with the general community their experience in fume hoods 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 SAMA (Scientific Apparatus Makers Association). The SAMA was an early attempt to provide guidance on lab fume hoods. The SAMA LF (and subsequent) are not considered the highest standard of care and should not be used as a sole guidance document. SEFA (Scientific Equipment & Furniture Association) The SEFA standard superseded the SAMA LF standard. The current SEFA standard is SEFA Again, the attempt to standardize the evaluation is laudable, but the standard should not be used as sole guidance for hood performance evaluation Not a copyright protected document Not a copyright protected document 19 20

6 NSF IES The National Sanitation Foundation provides non-regulatory guidance and certification for biological safety cabinets. Institute of Environmental Sciences Recommended Practices (IES-RP- CC-002) The NSF standards are not binding on US industry. National consensus standards State of the art 21 Primarily deals with filters National consensus standard State of the art 22 Hood Classifications Structural design dictates hood objectives and classification. Hoods are classified based on their ultimate goal. Some hoods protect only the item in the hoods, some provide protection only for the employee. Some hoods are appropriate for biological contaminants, while other hoods are inappropriate for biological contaminants. Class I Biosafety Cabinet Provides glove box protection for the employee does not protect the contents 23 24

7 Class I Biosafety Cabinet Class III Biological Safety Cabinet Class III provides glovebox protection to the employee AND the experiment. The entire box in maintained under negative pressure Class IIA Biological Safety Cabinet The Class IIA cabinet protects the employee and the experiment. The fan and plenum are contaminated and the plenum is under positive pressure. Class IIA Biological Safety Cabinet Alternative IIA Configuration 27 28

8 Class II B Biological Safety Cabinet The fan is not contaminated in the Class II B. Protection is provided to the employee and to the experiment Class IIB Biological Safety Cabinet In this version of a IIB, the plenum is maintained under negative pressure Laminar Flow Hoods Laminar flow hoods do not protect the employee Laboratory Fume Hoods The standard laboratory fume hood or fume cupboard is essentially a Class I Safety Cabinet. It affords the employee protection, but does not protect the experiment. In its most basic design, the fume hood simply draws air through the opening and evacuates the air outside the building. The velocity of the air through the face is directly proportional to the evacuatory volume and inversely proportional to the cross sectional area of the opening of the face (called the plane of the sash)

9 Single Greatest Confounder Reverse vector flow Negative pressure zones Disrupted air flow Supply vents Doors Windows Traffic Poor design Underrated Poor location in lab Not synced with ventilation design Single Greatest Confounder Reverse vector flow Poor installation Fans installed backward Poor work practices Personnel modifications Lab coats Work area locations Work configurations User adjustable baffles Negative pressure zones Negative Pressure Zones In the simple laboratory fume hood, the employee creates a negative pressure zone at the face of the hood when the employee occupies the face of the hood 35 36

10 Negative pressure zones To eliminate the negative pressure zone, auxiliary air may be brought in from the top and forced to fill the negative pressure zone Negative pressure zones Or air may be brought in from the side Preliminary Assessment Identification of confounders Equipment In Hood Type of equipment Excessive heat load? Jet producer? Biological contaminants? Radiological contaminants? Location of equipment Is the equipment raised? Face clear of obstructions? Gas cylinders? Preliminary Assessment (cont) Lab coats? Broken parts? Custom modifications? Bottom air foil? Cluttered with storage? Location of work (outside the spill control area?) Blocked aux. vents? 39 40

11 Preliminary Assessment (cont) Blocked bottom slot? Is spill control in place? Will the sash hold all positions? Is the electrical on GFI? Is perchloric acid used in the hood? Is there a wash-down on a perchloric hood? Presence of Strouhal frequencies? Is work being performed outside spill control area? 41 Preliminary Assessment (cont) Manufacturer? Currently in use? Date of last inspection Last efficacy rating Have baffles been adjusted? Have blast gates been adjusted? Roof top inspection (terminal caps and air intakes 42 ASHRAE Protocol There are many important confounding factors in the safe operation of laboratory hoods that are not described in the standard. These include: Cross-drafts Internal obstructions Thermal challenge Work practices Work in progress Rate of Response 43 Fume Challenges TiO2 Fume Tests Face Challenge The entire face of the hood is challenged at the plane of the sash At the point of work which is furthest from the back plenum. Does the fume escape from the plane of the sash? Does the fume reverse into the worker's breathing zone? 44

12 Fume Challenges (cont) Equipment Challenge All points of exposure are challenged. Bottom Foil Is the bottom foil free and clear? Evacuatory Observations Presence of static cells or reverse vector flow cells? Presence of roll? Fume Challenges (cont) Exterior Challenge (challenge from behind) Does the fume travel in a laminar fashion around the worker? Does the fume sweep back out from the hood interior? High Volume (recovery) Challenge Determines ability to contain catastrophic release No correlation between face velocity and intrinsic safety No "scientific" basis for a 100 lfpm criteria lfpm is an engineering design criteria Higher face velocities equal greater turbulence Face Velocities Hitchings Associates, PC used with kind permission ASHRAE 110 Control Level (ppm) Velocity vs Control Mean Face Velocity vs. ASHRAE 110 Control Level Population = 176 Hoods Correlation Coefficient = Mean Face Velocity (fpm) 47 Hitchings Associates, PC used with kind permission 48

13 Face Velocity An exhaustive study conducted for the EPA, concluded that fume hood face velocities of 50 FPM would usually suffice if the particle kinetics for aerosols or the molecular diffusion of gases and vapors were the only forces to overcome. The study also concluded that face velocities of 80 to 100 FPM are adequate if the overall installation can be rated as good to excellent. The increased turbulence within the hood and around the operator when higher velocities (150 FPM) were used, compounded the bad performance of installations rated poor. (Laboratory Fume Hood Standards Recommendations for the USEPA, R.I. Chamberlin and J.E. Leahy, 1/15/78. Contract No ) 49 Sash/Velocity Relationship In most lab fume hoods, the velocity of the air at the face as the sash is lowered would be excessive. Therefore, a bypass baffle is added to the casing. The baffle opens as the sash is lowered, allowing room air to enter the hood interior. In this way, the hood static pressure is maintained, but the flow of air through the face opening is lower than would normally be predicted. Virtually all standard hoods are now by-pass hoods. To measure the evacuatory volume or face velocity with the sash in any position other than fully open, may result in erroneous data. Determining the sash level at which a 100 lfm face velocity is achieved is a useless and misleading exercise providing absolutely no information about the functioning of the hood. 50 Velocity Readings Velocity Readings - Anamometery Hitchings Associates, PC used with kind permission Hitchings Associates, PC used with kind permission 51 52

14 Probe Anamometry Measuring Face Velocities Degree of Yaw A % Accurate B % Accurate Source: Air Flow Ltd. UK Miscellaneous Readings Auxiliary Velocities Anemometry or delta P readings as permitted by the size of the opening. Readings taken every 6 inches. Optimal range is 30 to 70% of evacuatory Q By-pass Baffle Check Room Air Location of doors and windows are noted Velocity readings of cross drafts are measured parallel to the sash In the Y axis In the X axis Optimally, cross drafting should not exceed 25 lfpm Sash is lowered to 6 inches; equidistant center-line readings taken "Closed to open" ratio (C:O) should be no greater than 3 and no less than 0.2. C:O ratios greater than 3 are indicative of a dysfunctional by-pass baffle (or a hood that is a simple cabinet). 55 Effects of doors and windows are evaluated with fume as the doors are opened and closed. Effects of traffic are evaluated 56

15 Room Air In a published study, the authors concluded that "The terminal throw velocity through the grilles had a greater effect on the spillage rate (from the hood) than the face velocity of the hood." Laboratory Fume Hoods: Influence of Room Air Supply K.J. Caplan and G.W. Knutson, ASHRAE Transactions, Vol. 84, No 2, Category I Evaluation Categories The challenge fume is adequately captured at the face of the hood and progresses into the hood in a laminar manner where it is exhausted. The hood is considered to be operating in a manner which indicates that adequate protection will be provided by the user Category II Evaluation Categories The challenge fume reverses and migrates toward the user but is captured before reaching the user's breathing zone; OR static cells are present which also result in the gradual migration of contaminant toward the user but is captured and exhausted. The hood is considered to be operating in a non-optimal fashion. Evaluation Categories Category III The challenge fume migrates directly to the user's breathing zone or escapes from the interior of the hood, spilling into the surrounding air. The hood is considered to be dysfunctional. The recommendation is that the hood not be used for the protection against harmful contaminants