WKU Laboratory Ventilation Management Program

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TABLE OF CONTENTS

 

POLICY

Laboratory exhaust ventilation systems designed, constructed, maintained and used at Western Kentucky University shall comply with the specifications and standards set forth in this document and in the publications listed in Appendix A. This Laboratory Ventilation Management Program has been created based upon the standards currently in practice at the University of Massachusetts, Amherst. Written permission for use was obtained from that university’s Environmental Health & Safety Department.

New, renovated and established fume hood systems will be tested using the Procedures for Testing Fume Hood Systems (Appendix C). Fume hood systems that do not meet the testing criteria and specifications will not be accepted for use. When a fume hood fails to meet acceptable performance requirements the hood will be declared out of service. The Environmental Health and Safety Department will evaluate these systems. A sample fume hood inspection report is provided in Appendix D. See Appendix E for Responsibilities for the Proper Operation and Use of Fume Hoods.

OBJECTIVES

The intention of this document is to set a standard for the design, construction, maintenance and use of laboratory ventilation in order to maintain acceptable air quality in the laboratory building and surrounding areas. This standard outlines criteria for stack heights, exhaust exit velocities, and design considerations that shall be considered and implemented at Western Kentucky University. This document together with existing design standards will determine requirements for laboratory exhaust ventilation systems. These requirements do not preclude adherence to good engineering practice and the Kentucky Building Code and standards referenced therein. These requirements will be included in contract specifications for all future contracts for fume hood systems submitted by Western Kentucky University.

INTRODUCTION

This standard will concentrate on the aspects of fume hood system design and operation that are critical to protecting the health and safety of faculty, students, and visitors and also minimizing nuisance odors. Properly designed systems function to capture contaminants from the work area and disperse them in the outside environment. Exhaust stacks function to release contaminants from the inside of a building in order to minimize contaminant reentrainment. The critical design aspects of fume hood systems that are discussed in this document are: the quality of the fume hood enclosure, the quality and quantity of supply air provided to the fume hood, face velocity of the fume hood, exhaust stack height and exit velocity of air being exhausted from the stack. In addition, effluent dispersal is contingent upon factors such as exhaust stack / air intake separation, stack height, stack height plus momentum, topography of the building and surrounding environment, and wind dynamics.

Although system performance depends heavily on the above design elements it must be noted that the fume hood performance in a room is affected by room layout and supply air distribution. System performance depends on the fan and duct layout as well as fan type and discharge conditions.

FUME HOOD DESIGN AND CONSTRUCTION

Hood Purchase Specifications and Evaluations

A fume hood that is appropriate for the purpose should be chosen. General guidelines on types of hoods and their application are presented in the American Conference of Governmental Industrial Hygienist’s (ACGIH) Industrial Ventilation Manual.

Laboratory fume hoods and associated exhaust ducts should be constructed of non- combustible, nonporous material that will resist corrosion. They should be equipped with vertical or horizontal sashes that can be closed, airfoils built into the fume hood at the bottom and the sides of the sash opening, and baffles to attain a uniform face velocity under different conditions of hood use. Combination horizontal and vertical sashes shall be provided unless special conditions dictate otherwise. Additionally, recognized good design and construction features are listed in ANSI/AIHA Z9.5 1992.

Fume hoods should be tested before a hood leaves the manufacturer using the ANSI/ASHRAE requirements for Class 1 hoods including a tracer gas performance of AM(as manufactured) 0.05ppm or better at a tracer gas release rate of 4.0 liters per minute. Documentation shall be provided with the results of the test. Performance is measured by specific tests.

1. Flow visualization,

2. Face velocity measurements,

3. Test method for Variable-Air-Volume (VAV) Fume Hoods,

4. VAV Response Test, and

5. Tracer gas containment.

Flow visualization qualitatively tests a hood’s ability to contain vapors. This test consists of a small local challenge (use of a smoke tube), and a gross challenge (use of a smoke candle or smoke generator) to the hood. Smoke is released in the hood to visually determine if a hood or associated duct work leaks as it is actually used.

Face velocity measurements determine the average velocity of air moving perpendicular to the hood face. The measurement is usually expressed in feet per minute (fpm). Face velocities will often provide information concerning the fume hood’s ability to properly control contaminants.

A tracer gas leak test will quantitatively determine if the fume hood is properly containing contaminants. A tracer gas is released in the hood and a continuous-reading instrument is positioned outside the hood to monitor for the escape of the tracer gas. The preferred tracer gas is sulfur hexafluoride.

Face Velocity

Each variable air volume hood shall maintain an average face velocity of 80-150 fpm with the sash at a working height of no less than 12 inches. Each constant volume hood shall maintain an average face velocity of 80-150 fpm in the half open position. A written request for an exception to this requirement must be submitted to EH&S and will be granted only by EH&S. Face velocity measurements are to be made with a recently calibrated mechanical or electrical anemometer. Measurements should be made of 1 square foot areas across the face of the hood and no single face velocity measurement should be more than plus or minus 20% of the average. For further information, refer to ANSI/ASHRAE 111-1988, Practices for Measurement, Testing Adjusting, and Balancing of Building Heating, Ventilation, Air-Conditioning, and Refrigeration systems.

Supply Air

The proper volume, distribution, and quality of supply air shall be provided to laboratories containing fume hoods. ANSI/AIHA Z9.5 1992 and ANSI/ASHRAE 62 provide these standards. Make up air (replacement air) should be equal to at least 95% of the volume exhausted from the laboratory. This air shall not be re-circulated from other laboratory areas. Although laboratory supply air seldom requires air cleaning, ASHRAE (HVAC Application Handbook 1995) provides technical information for the reduction of contamination from atmospheric dust and dirt.

Air supply systems for rooms containing chemical fume hoods shall not create room air drafts at the face of any hood greater than one half (and preferably one third) the face velocity of the hood. For most laboratory hoods, this means 50 fpm or less terminal throw velocity at 6 feet above the floor. ACGIH’s "Industrial Ventilation - A Manual of Recommended Practice" provides design criteria to help achieve these standards.

Variable Air Volume Fume Hoods

Variable-air volume fume hoods shall be installed unless accepted design practice dictates otherwise. A VAV hood is one that is fitted with a face velocity control that varies the amount of air exhausted from the fume hood in response to the sash opening to maintain a constant face velocity. These hoods produce an acceptable face velocity over a relatively large sash opening and also provide significant energy savings by reducing the flow rate from the hood when it is closed.

Exhaust Stack Discharge and Exit Velocities

Exhaust stacks shall be designed and built to prevent re-circulation of contaminated air from the fume hood exhaust system into the fresh air supply of the facility or adjacent facilities. The effluent exhaust shall escape the building envelope. The stack shall also provide significant effluent dispersal so that effluent downwash does not occur at ground level. They shall be designed and built with the latest applicable ASHRAE standards and using ANSI/ASHRAE Z9.5. ASHRAE’s 1997 Fundamental Handbook and the publication "Laboratory Stack Height Determination and Evaluation Methods" present three methods for specification and evaluation of stack heights from laboratory hood exhaust fans.

Effluent discharge shall be:

  1. direct to the atmosphere (unless treated for re-circulation).
  2. in compliance with federal, state and local air emission regulations.
  3. released so that reentry of effluent from the discharging building or a surrounding building is reduced to allowable concentrations inside of the building. (Allowable concentrations shall be determined using information on the nature of the contaminants to be released, recommended industrial hygiene practice, and applicable safety codes.)
    4.

Exhaust discharge from stacks shall:

  1. be in a vertical up-draft direction at a minimum of 10 ft above adjacent roof lines and located with respect to surrounding air inlets as to avoid contaminant re-entry.
  2. have a minimum exit velocity of 3000 fpm.
    3.

Re-circulating Hoods

Re-circulating or ductless fume hoods are not permitted for the removal of chemical contaminants.

Special Laboratory Fume Hoods

ANSI/AIHA Z9.5 1992 provides standards for non-traditional laboratory fume hoods. These hoods include perchloric acid fume hoods, walk-in fume hoods, and glove boxes. All class II biological safety cabinets must meet the National Sanitation Foundation

Standard Number 49 for Class II Biohazard Cabinetry for design, manufacturing and testing.

TESTING FUME HOOD EXHAUST SYSTEMS AND BIOLOGICAL SAFETY CABINETS

All new and renovated fume hoods will be tested after installation and before use. They shall also be tested annually, as will established fume hoods. See Procedures for Testing Fume Hoods (Appendix C).

The operational integrity of a new biological safety cabinet (BSC) must be validated by certification before it is put into service or after a cabinet has been repaired or relocated. In addition, it will be the responsibility of the faculty member to have BSC tested and certified annually. An accredited Biohazard Cabinet Field Certifier using National Sanitation Foundation (NSF) Standard Number 49 for Class II Biological Safety Cabinets will perform certification.

USE OF LABORATORY HOODS

All personnel using fume hoods, biological safety cabinets, and glove boxes will follow the policies and procedures outlined in Western Kentucky University’s Chemical Hygiene Program (CHP). ANSI/AIHA Z9.5 1992 and ACGIH’s Industrial Ventilation Manual provide additional work practices to minimize emissions and employee exposure when working with fume hoods.

CDC/NIH’s publications "Bio-safety in Microbiological and Biomedical Laboratories" and "Primary Containment for Biohazards: Selection, Installation, and Use of Biological Safety Cabinets" provide additional information on the use of biological safety cabinets. Horizontal and vertical laminar flow clean benches are not biological safety cabinets. These clean benches provide a very clean environment for the manipulation of non-hazardous materials and can be used for activities such as the dust-free assembly of sterile equipment or electronic devices. Since the operator sits in the downstream exhaust from the clean bench, this equipment must never be used for the handling of toxic, radioactive, infectious, or sensitizing materials.

DECONTAMINATION AND REMOVAL OF FUME HOOD SYSTEMS OR BIOLOGICAL SAFETY CABINETS

When a fume hood is scheduled for removal, the hood, fan, and associated ductwork must be tested for the presence of radioactive materials and hazardous chemicals e.g. perchlorate salts, asbestos, oxidizers, sulfides, cyanides, lead, and mercury. EH&S will determine the need for testing and decontamination of the hood and ductwork. If decontamination is necessary, fume hood(s) must be decontaminated before removal. Biological safety cabinets must be decontaminated before removal or a move to a different location. Costs associated with testing and/or decontamination shall be included in the total project cost.

CONTRACTORS WORKING WITH FUME HOODS AND ASSOCIATED FANS AND DUCTWORK

Before beginning work, all contractors and subcontractors, involved with a renovation project involving fume hoods and associated fans and ductwork must consult with EH&S for recommendations for training and personal protective equipment for their employees.

APPENDICES

APPENDIX A

PUBLICATIONS

ANSI/ASHRAE 110-1995 "Method of Testing Performance of Laboratory Fume Hoods." (1995).

Available from:

ASHRAE

1791 Tullie Circle, NE

Atlanta, GA 30329

ANSI/AIHA Z9.5 1992 "American National Standard for Laboratory Ventilation." American Industrial Hygiene Association. 1992.

Available from:

AIHA

2700 Prosperity Avenue

Suite 250

Fairfax, VA 22031

NFPA Standard 45. National Fire Protection. Standard on fire protection for laboratories using chemicals.

OSHA 29 CFR 1910. Occupational Exposures to Hazardous Chemicals in Laboratories; Final Rule.

Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Committee on Prudent Practices for Handling, Storage, and Disposal of Chemicals in Laboratories. National Academy Press. Washington, D.C., 1995.

APPENDIX B

DEFINITIONS

BUILDING ENVELOPE: the three-dimensional space surrounding a building containing the building’s makeup air.

DOWNWASH: pollutants discharged from an exhaust stack that travel towards the ground due to insufficient discharge velocities, poor wind dispersion, and physical obstructions.

EXHAUST AIR: the air that is removed from an enclosed space and discharged into the atmosphere (ANSI/AIHA Z9.5, 1992).

FACE VELOCITY: average velocity of air moving perpendicular to the hood face, usually expressed in feet per minute (fpm) or meters per second (m/s) (ANSI/ASHRAE 110, 195).

GLOVE BOX: a boxlike structure provided with tight-closing doors or air locks, armholes with impervious gloves sealed to the box at the armholes, and exhaust ventilation to keep the interior of the box at negative pressure relative to the surroundings (ANSI/AIHA Z9.5, 1992).

HOOD FACE: the of minimum area at the front portion of a laboratory fume hood through which air enters when the sash(es) is (are) fully opened, usually in the same plane as the sah(es) when sash(es) is (are) present (ANSI/ASHRAE 110, 1995).

INTERNAL CONDENSATION: fumes and vapors that condense into liquids inside of the exhaust stack.

LABORATORY FUME HOOD: a boxlike structure enclosing a source of potential air contamination, with one open or partially open side, into which air is moved for the purpose of containing and exhausting air contaminants, generally used for bench-scale laboratory operation but not necessarily involving the use of a bench or a table (ANSI/ASHRAE 110, 1995).

LPM: liters per minute (ANSI/ASHRAE 110, 1995).

MAKEUP AIR: outside air drawn into a ventilation system to replace exhaust air (ANSI/AIHA Z9.5, 1992). Makeup air MUST always be provided when any exhaust system is designed and installed.

PERCHLORIC ACID HOOD: a fume hood constructed with water wash so it is safe for use with perchloric acid or other reagents that might form flammable or explosive compounds with organic materials of construction (ANSI/AIHA Z9.5, 1992).

RECIRCULATION: air withdrawn from a space, passed through a ventilation system, and delivered again to an occupied space (ANSI/AIHA Z9.5, 1992).

REENTRY: The flow of containment air that has been exhausted from a space back into the space through air intakes or openings in the walls of the space (ANSI/AIHA Z9.5, 1992).

REPLACEMENT AIR: see makeup air.

RETURN AIR: air being returned from a space to the ventilation fan that supplies air to a space (ANSI/AIHA Z9.5, 1992).

SPECIAL PURPOSE HOOD: an exhaust hood, not otherwise classified, for a special purpose such as, but not limited to, capturing gases from equipment such as atomic absorption, gas chromatographs, liquid pouring or mixing stations, and heat sources (ANSI/AIHA Z9.5, 1992).

VARIABLE AIR VOLUME FUME HOOD: a fume hood designed so the exhaust volume is varied in proportion to the opening of the hood face by changing the speed of the exhaust blower or by operating a damper in the exhaust hood (ANSI/AIHA Z9.5, 1992).

VELOCITY: speed and direction of motion (ANSI/AIHA Z9.5, 1992).

WALK-IN HOOD: a fume hood designed to be floor mounted with sash and/or doors for closing the open face (ANSI/AIHA Z9.5, 1992).

APPENDIX C

PROCEDURES FOR TESTING FUME HOOD SYSTEMS

Applicability: This test is to be conducted when new hoods are installed or when existing hoods are included as part of a significant renovation as a condition of acceptance. In addition tests will be conducted annually to check the performance of established fume hoods or whenever a significant change is made to the operating characteristics of the hood. Tests to be performed include face velocity measurements and containment tests.

Test conditions:

1. General room ventilating systems, both supply and exhaust, including fume hood exhaust, must meet design specifications and shall be in full normal operation. Airflow systems in the laboratory shall be properly balanced and commissioned prior to this test. Laboratories must be under negative pressure relative to corridor unless special design conditions prevail.

2. Hoods are tested in fully open position, half-open position, and 25% open position.

3. All other hoods in the same room are in half-open position.

4. All other hoods on the same floor exhaust system are in half-open position.

5. The hood being tested should be empty.

6. The doors to the laboratory will be closed.

7. When adjustments are made to hood sashes, supply and exhaust air in the room will be allowed to stabilize before testing is done.

8. Hood monitor, where applicable, is calibrated and not in alarm.

Determination of Average Face Velocity for Variable Air Volume (VAV) Hoods:

  1. The open face of the hood shall be divided into imaginary rectangles (zones) of equal area approximately 1 square foot and velocity shall be measured in each rectangle.
  2. Instruments used: EXTECH Hot Wire Thermo-Anemometer..
  3. Average the readings to determine average face velocity.
  4. Note reading of face velocity on anemometer.
  5. Average face velocity must be 80-150 fpm at maximum allowed hood opening. Maximum opening is the point above which the face velocity falls below 80 fpm.
  6. Anemometer readings must be within +/-20% of the average face velocity.
  7. Face velocities will also be measured at the one half and one quarter open positions. The average face velocities at these openings should be +/-10% of the average at the fully open position.
    8.

Determination of Average Face Velocity for Constant Air Volume Hoods:

1. The open face of the hood shall be divided into imaginary rectangles of equal area approximately 1 square foot and velocity shall be measured in each rectangle.Instruments used: EXTECH Hot Wire Thermo-Anemometer.

2. Note reading of face velocity on anemometer.

3. Average the readings to determine average face velocity.

4. Average face velocity must be 80-150 fpm at the one-half open position or as a minimum at the operational position of 12 inches.

5. Anemometer readings must be within +/-20% of the average face velocity.

Smoke Testing To Determine Direction of Airflow and Air Turbulence and Containment Reentry:

Using a smoke tube, puff smoke 6 inches within the face of the hood around the outside edge of the opening. Determine direction of smoke flow. If visible fumes flow out of the front of the hood, make necessary adjustments.

Ignite a smoke candle in the hood and visually observe if there is leakage of smoke from the ductwork or if smoke is being drawn back into building or surrounding buildings.

Conditions For Passing Hoods:

  1. General room ventilating systems, both supply and exhaust, including fume hood exhaust shall be in full normal operation.
  2. Hood must have an average face velocity of 80 fpm at a sash height of no less than 12 inches.
  3. Hood must pass the smoke testing.
  4. There must be no leakage of exhaust from ductwork and no reentry of hood exhaust into buildings.
    5.

    APPENDIX D

    ANNUAL FUME HOOD INSPECTION FORM

  • The Annual Fume Hood Inspection Form can be found at : Form
    •

APPENDIX E

RESPONSIBILITIES FOR THE PROPER OPERATIONAL USE OF FUME HOODS

Environmental Health and Safety:

  1. Inspects the entire fume hood operating systems including the fume hood, associated ductwork, exhaust blowers, and stacks.
  2. Places a sticker on fume hoods indicating maximum working sash height and the average face velocity at this height if the hood passes inspections and is deemed suitable for use.
  3. Places a "Do Not Use" sign on the hood sash if the hood fails to pass inspections and is deemed unsuitable for use.
  4. Puts in a work order on behalf of the Department Head to Facilities Management for repair.
  5. Notifies the Department Head and Facilities Management of any hoods that are placed out of service.

Facilities Management:

1. Make all necessary repairs/modifications to the fume hood operating system, and any associated equipment that affects the fume hood operating system in order to make the entire system safe to use.

2. Notify the Environmental Health and Safety Department (EH&S) upon completion of all repairs/modification. EH&S will then retest the system.

Department Head:

1. Ensure that any hoods that are placed out of service are not used until notified by EH&S that they are suitable for use.

2. Attend all required health and safety training sessions.

3. Do not use fume hoods that are out of service.

4. Report fume hoods which are not operating properly, accidents, and any unhealthy and unsafe conditions to EH&S.

5. Notify EH&S of any pre-existing health conditions that could lead to serious health situations when using a fume hood.

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