Laboratory Hoods Use and Evaluation Topics of …forensic-applications.com/hoods/NCAR/NCAR_Handouts2.pdfLaboratory Hoods Use and Evaluation Caoimhín P. Connell Forensic Industrial

Thoughts On Hood Evaluations

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Laboratory HoodsUse and Evaluation

Caoimhín P. ConnellForensic Industrial HygienistForensic Applications, Inc.185 Bounty Hunter Lane

Bailey, COwww. www.forensic-applications.com

NCAR October 29, 2010

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Topics of DiscussionRegulatory issues and Industry Protocols

Hood Classifications

Evaluation methods

Performance Confounders

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Pertinent Standards and ProtocolsOHSANIOSHANSI/ASHRAENFPAAIHAACGIHSAMASEFAMiscellaneous

International Standards

German DIN 12 924

British HSE DD 191

Canadian CSA: Standard Z316.5-04 (Fume Hoods and Associated Exhaust Systems)

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OSHA RegulationsOSHA has extended its authority into the lab industry with 29 CFR §1910.1450; 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 (§1910.1450(e)(3)(iii)).


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OSHA Although OSHA does specify minimum face velocities for laboratory fume hoods in several compound specific standards (29 CFR §§1910.1003, .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. 830. (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.

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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.

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NIOSH

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.

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CDC (NIOSH)/NIH

The CDC pamphlet titled "BIOSAFETY IN MICROBIOLOGICAL and BIOMEDICAL LABORATORIES" does not provide performance criteria for control devices.


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ASHRAE

ASHRAE Standard 110-1995Method of Testing Performance of Laboratory Fume HoodsState-of-the-artNational consensus standard

The American Society of Heating, Refrigeration and Air-conditioning Engineers is a nonregulatory profit making organization. Although it publishes "standards" none of the standards are binding on U.S. businesses per se.

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Evaluation Protocols ASHRAEThe ANSI/ASHRAE 110-1995 method METHOD OF TESTING

PERFORMANCE OF LABORATORY FUME HOODS (ISSN 1041-2336) supersedes the ANSI/ASHRAE 110-1985.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 fora 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.

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ASHRAE 110 ProtocolThe method consists of three parts:

1) Flow visualization2) Face velocity measurements3) 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.

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ASHRAE 110 ProtocolThe method consists of three parts:

1) Flow visualization2) Face velocity measurements3) 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.


ASHRAE Tracer Gas Containment Test

TRACERGAS

SOURCE(SF6)

TRACER GASANALYZER

TRACERGAS

EJECTORMANNEQUIN

TRACER GASSAMPLER/DETECTOR

HOOD

TRACER GAS

CLOUD

Tracer GasAnalyzer

© Hitchings Associates, PC used with kind permission

Mannequin & Tracer Gas Detector© Hitchings Associates, PC used with kind permission

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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

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ANSI/AIHA

ANSI Z9.5-2003 (Laboratory Ventilation)

ANSI Standard Z129.1-2010 (Hazardous workplace chemicals)

State of the artNational consensus standards


NFPANFPA 45-2011 Standard on Fire Protection for Laboratories Using Chemicals

State of the artNational consensus standards

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SAMAandSEFA

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.

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SAMA(Scientific Apparatus Makers Association). The SAMA was an early attempt to provide guidance on lab fume hoods. The SAMA LF-10-1981 (and subsequent) are not considered the highest standard of care and should not be used as a sole guidance document.

Not a copyright protected document

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SEFA (Scientific Equipment & Furniture Association) The SEFA 1-1992 standard superseded the SAMA LF-10 1981 standard. The current SEFA standard is SEFA 1.2 1996. 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


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NSFThe National Sanitation Foundation provides non-regulatory guidance and certification for biological safety cabinets.

The NSF standards are not binding on US industry.

National consensus standardsState of the art

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IESInstitute of Environmental Sciences Recommended Practices (IES-RP-CC-002)

Primarily deals with filtersNational consensus standardState of the art

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Hood ClassificationsStructural 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.

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Class I Biosafety Cabinet

Provides glove box protection for the employee –does not protect the contents


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Class I Biosafety Cabinet

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Class III Biological Safety CabinetClass III provides glovebox protection to the

employee AND the experiment. The entire box in maintained under negative pressure.

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Class IIA Biological Safety CabinetThe Class IIA cabinet protects the employee and the experiment. The fan and plenum are contaminated and the plenum is under positive pressure.

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Class IIA Biological Safety CabinetAlternative IIA Configuration


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Class II B Biological Safety CabinetThe fan is not contaminated in the Class II B. Protection is provided to the employee and to the experiment

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Class IIB Biological Safety CabinetIn this version of a IIB, the plenum is maintained

under negative pressure

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Laminar Flow HoodsLaminar flow hoods do not protect the employee

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Laboratory Fume HoodsThe 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).


Single Greatest ConfounderReverse vector flow

Negative pressure zonesDisrupted air flow

Supply ventsDoorsWindowsTraffic

Poor designUnderratedPoor location in labNot synced with ventilation design

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Single Greatest ConfounderReverse vector flow

Poor installationFans installed backward

Poor work practicesPersonnel modificationsLab coatsWork area locations Work configurationsUser adjustable baffles

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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

Negative Pressure Zones

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To eliminate the negative pressure zone, auxiliary air may be brought in from the top and forced to fill the negative pressure zone

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Or air may be brought in from the side.

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Preliminary AssessmentIdentification of confounders

Equipment In HoodType of equipmentExcessive heat load?Jet producer?Biological contaminants?Radiological contaminants?Location of equipmentIs the equipment raised?Face clear of obstructions?Gas cylinders?

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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?


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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?

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Preliminary Assessment (cont)Manufacturer?Currently in use?Date of last inspectionLast efficacy ratingHave baffles been adjusted?Have blast gates been adjusted?Roof top inspection (terminal caps and air intakes

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ASHRAE ProtocolThere are many important confounding factors in the safe operation of laboratory hoods that are not described in the standard. These include:

Cross-draftsInternal obstructionsThermal challengeWork practicesWork in progressRate of Response

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Fume Challenges

TiO2 Fume TestsFace ChallengeThe 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?


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Fume Challenges (cont)Equipment Challenge All points of exposure are challenged.

Bottom FoilIs the bottom foil free and clear?

Evacuatory ObservationsPresence of static cells or reverse vector flow cells?Presence of roll?

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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) ChallengeDetermines ability to contain catastrophic release

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Face VelocitiesNo correlation between face velocity and intrinsic safety

No "scientific" basis for a 100 lfpm criteria

80-120 lfpm is an engineering design criteria

Higher face velocities equal greater turbulence


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Velocity vs ControlMean Face Velocity vs. ASHRAE 110 Control Level

0.0001

0.001

0.01

0.1

1

10

100

40 60 80 100 120 140Mean Face Velocity (fpm)

ASH

RA

E 11

0 C

ontr

ol L

evel

(ppm

)

Population = 176 Hoods Correlation Coefficient = -0.24



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Face VelocityAn 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. 68-01-4661)

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Sash/Velocity RelationshipIn 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.

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Velocity Readings

© Hitchings Associates, PC used with kind permission 52

Velocity Readings - Anamometery



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Probe Anamometry

Degree of Yaw

-30° -20° -10° 0° 10° 20° 30°

A % Accurate -78 -88 -96 0 98 -98 -86

B % Accurate -96 -97 -99 0 97 97 -99

Source: Air Flow Ltd. UK 54

Measuring Face Velocities

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Miscellaneous ReadingsAuxiliary VelocitiesAnemometry 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

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).

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Room AirLocation of doors and windows are noted

Velocity readings of cross drafts are measured parallel to the sash

In the Y axisIn the X axis

Optimally, cross drafting should not exceed 25 lfpm

Effects of doors and windows are evaluated with fume as the doors are opened and closed.

Effects of traffic are evaluated


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Room AirIn 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, 1978.

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Evaluation CategoriesCategory IThe 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.

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Evaluation CategoriesCategory II

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.

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Evaluation CategoriesCategory IIIThe 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.

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