Environment, Health and Safety Manual - Chapter 05.19: Occupational Safety Policies - Laboratory Ventilation Policy


Environment, Health and Safety Manual - Chapter 05.19: Occupational Safety Policies - Laboratory Ventilation Policy


The University of North Carolina at Chapel Hill (University) is committed to providing students, faculty and staff with engineering controls that minimize their exposure to hazardous materials. This policy addresses the installation, removal, change, and monitoring of ducted and non-ducted equipment used to control exposure to chemicals, toxins, radionuclides, and biohazard agents at the University.


Types of Protection

Common hoods and cabinets used at UNC-CH that provide worker protection by enclosing the hazardous operation include the chemical fume hood and the biological safety cabinet (BSC). The Clean Bench does not offer worker protection. For more information about safe use of chemical hoods, refer to the UNC Laboratory Safety Manual, Chapter 17. For more information about the safe use of biosafety cabinets, refer to the UNC Biological Safety Manual, Chapter 9.

Types of Protection and Environment Table
Type Worker Product Environment
Snorkel Units
(Protection from vapors and gases)
Chemical Fume Hoods
(Protection From Vapors And Gases)
Biological Safety Cabinets
(Protection From Particulates and minute/small amounts of gases)
Clean Benches
(No Worker Protection)
Ductless Fume Hoods
(Protection From Vapors And Gases)

Selection and Purchase

University Materials & Disbursement Services requires the approval of the Directors of Facilities Services and Environment, Health and Safety (EHS) (or their designees) for the purchase of a ducted biological safety cabinet, a snorkel unit or a ducted or ductless chemical fume hood. Examples of Director designees are Engineering Supervisors, Biological Safety Officers and Chemical Hygiene Officers. Investigators who wish to bring Chemical Fume Hoods or Biological Safety Cabinets with them from a previous location must seek approval from EHS prior to shipment.

All newly installed Chemical Fume Hoods and ducted Biological Safety Cabinets shall be equipped with a static pressure gauge and alarm to continuously monitor hood airflow. Gauges shall be selected to operate at 50% of full range. Alarms shall be calibrated to alarm at +/- 20% of designed airflow.

The purchase and installation of an auxiliary air hood is not permitted.

Clean Benches may not be approved for use with hazardous materials.

The purchase and installation of ducted Biological Safety Cabinets must follow the Flammable Gases Policy.

The purchase and installation of a ductless fume hood must be approved by the EHS Director (or designee) and filter-changing/testing conducted at the expense of the PI or department and documented on the Laboratory Safety Plan (Schedule B).

Ductless fume hoods are designed to remove hazardous fumes and vapors from the work area by passing the exhaust air through a filter and/or adsorbent, such as activated charcoal. Because of the potential for unregulated use and personnel exposure through a “breakthrough” and desorption of vapors from the hood’s filtering system, EHS recommends using ducted hoods wherever possible. Ductless hoods should be used only when ducted hoods cannot be reasonably utilized or accommodated.



  • Users of ducted and ductless chemical fume hoods and biological safety cabinets are responsible for maintaining the unit in its original condition and minimizing storage of materials inside the hood/cabinet.
  • EHS will assess hoods during safety audits for materials that may potentially restrict

Students, faculty, staff, and Facilities Services personnel must not modify hoods or biosafety cabinets by drilling, cutting, adding or removing the hardware that was originally provided with the hoods. Such modifications are likely to degrade containment/performance of the unit and result in leakage of contaminants. An exception is installing a standard latticework of “monkey” bars at the rear of a chemical fume hood. Installers must follow the chemical fume hood manufacturer’s recommendations when installing these support bars. When in doubt, contact EHS. Any other proposed hood modifications must be reviewed and approved by EHS in advance and then tested following completion.

Alarms and Repair


Users of chemical fume hoods are responsible for contacting Facilities Services at 919-962-3456 if the hoods go into alarm or the gauge indicates poor hood performance.

Users of biological safety cabinets are responsible for contacting their third-party vendor (or EHS at 919-962-5507, if unknown) if the alarm sounds or the gauge indicates poor cabinet performance.

Users must follow shut down procedures and place a sign on the chemical fume hood or biological safety cabinet to notify others: “Out of Service/Do Not Use.”

Facilities Services will coordinate all responses to requests for ventilation system repair and contact EHS for a Safety Clearance Form as indicated in the worker’s Hazards Management Plan.

All system outages (planned or unplanned) require that laboratory notification, posting, and appropriate shutdown procedures be followed. Maintenance personnel shall follow all applicable OSHA standards as indicated in their Hazards Management Plan (e.g., hazard communication, lockout-tagout, personal protective equipment).

Directors or Department Chairs of the affected laboratories and EHS must be notified of all ventilation outages that will exceed four hours in duration.

Preventive Maintenance

Responsibility: Facilities Services

As with all mechanical systems, inspections and regular preventive maintenance are critical to ensure that laboratory exhaust systems operate without unscheduled interruptions in service. Facilities Services personnel maintain records of all inspections and corrective actions for each laboratory building. Depending on the item, inspections are done quarterly, semiannually or annually.

Laboratory occupants must receive advanced notification of planned fan stoppage and label the hood or ducted cabinet “Out of Service/Do Not Use” during the procedure.


Authorization for Removal, Change, or Installation of Laboratory Ventilation

A ducted or ductless chemical fume hood, snorkel unit or ducted biological safety cabinet cannot be installed at the University without the approval of the Directors of Facilities Services and Environment, Health and Safety, or their designees.

Authorization for Startup

To prevent the exposure of students, faculty and staff to volatile radionuclides, reproductive hazards, carcinogens, toxins, and biological hazards, EHS will not permit hazardous materials in a new laboratory until its ducted or ductless chemical fume hoods, ducted biological safety cabinets, and general ventilation system are performing according to the project’s design and manufacture’s specifications. The EHS Director, or designee, will make this decision based on the available information, including tests by the contractor, Facilities Services staff and EHS. All Chemical Fume Hoods:

  • Must pass the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 110 “as-installed” test, including a Sulfur Hexafluoride (SF6) challenge. Contact EHS for recommended testers. Testing shall be done at the user’s expense. See Addendum 1 for additional testing requirements.

Until the EHS Director or designee authorizes the startup of a new ducted or ductless chemical fume hood:

  • In an occupied laboratory, the hood will be posted with an “Out of Service/Do Not Use” sign.
  • EHS will not authorize the new laboratory for radioactive material
  • EHS will not move chemicals into the new laboratory.
  • EHS will instruct laboratory staff to not move any hazardous materials, including BSL-2 materials into the new
  • Third party commissioning is required for Variable Air Volume (VAV) laboratory hood systems.



  • The Building Manager, Department Administrator, and/or Project Manager will coordinate all requests for chemical fume hood or ducted biological safety cabinet removal and will notify EHS for Safety Clearance
  • Design Services of Facilities Services will oversee the airflow assessment and
  • Facilities Services Movers will not move a chemical fume hood or biological safety cabinet without an EHS Safety Clearance Form.

Because ducted chemical fume hoods, snorkel units and ducted biological safety cabinets may supply the majority of a room’s exhaust, removal of these units may require careful calculation to maintain safe and comfortable air in the space afterwards. Once the airflow assessment is signed off by Design Services of Facilities Services, EHS is called in to conduct a safety clearance for the physical removal of the hood. Biological safety cabinets must also obtain microbiological decontamination that meets or exceeds the NSF-49 standard prior to being moved. A chemical fume hood or biological safety cabinet is never to be moved without an EHS Safety Clearance Form.


Responsibility: Users or their Representatives, Facilities Services, EHS

The design of ducted chemical fume hood, snorkel units and ducted biological safety cabinet and overall laboratory ventilation systems must consider their physical environment and integration into the building’s supply and exhaust systems. System components include the hood or ducted cabinet, airflow alarm and gauge, supply and exhaust air requirements, general room ventilation, and Variable Air Volume (VAV) controls.

After installation or replacement and prior to use, the safety of the chemical fume hood or biological safety cabinet must be validated.

All Chemical Fume Hoods:

  • Must pass the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 110 “as-installed” test, including a Sulfur Hexafluoride (SF6) challenge. Contact EHS for recommended testers. Testing shall be included in the cost of the project. See Addendum 1 for additional testing
  • In laboratories designed to require that corridor doors be normally closed, require smoke puff tests at the bottom of the closed doors. (To pass, no smoke can escape into the )

All Biological Safety Cabinets:

  • Must pass the National Safety Foundation (NSF) standard 49 certification for Class II (Laminar Flow) Biosafety Cabinetry. Contact EHS for recommended
  • In laboratories designed to require that corridor doors be normally closed, require smoke puff tests at the bottom of the closed doors. (To pass, no smoke can escape into the )

Project budgets over $300K involving laboratories (both major and download) typically include major revisions to, or replacement of, existing HVAC systems, ductwork, hoods, cabinets, and control systems. For these projects, specifications for the design, purchase, installation, testing and balancing of chemical fume hoods, ducted biological safety cabinets and laboratory ventilation systems are detailed in the University Design Guidelines and may require approval from State Construction.

As described in the Guidelines, a rigorous, detailed review process for the entire ventilation system must be undertaken early in the project. Design and construction must follow coordinated, sequential steps to assure that all components of the system are considered and will perform properly.

Project budgets under $300K involving laboratory ventilation or the installation of new or replacement chemical fume hoods or ducted biological safety cabinets are managed through Design Services of Facilities Services.

  • Facilities Services will determine whether a building can adequately support a proposed chemical fume hood or ducted biological safety cabinet. An engineering assessment of existing mechanical and electrical systems must be performed before units can be added, removed, or
  • As much as practicable, specifications should rely on the University Design Guidelines, may require approval from State Construction, and design drawings and specifications shall be sealed by a Professional

Annual Hood and System Testing

EHS manages the University Biosafety Cabinet and Chemical Fume Hood Inspection and Airflow Measurement Program that ensures testing standards are met and maintains databases of all fumehood airflow testing and biosafety cabinet certifications at UNC-CH.

Chemical Fume Hoods

Responsibility: EHS

Testing shall occur with HVAC systems operating at 100%. Qualified and trained personnel shall conduct testing. At a minimum, the following test procedures will be followed:

  • Visual inspection for hood damage, modifications or congestion
  • Face velocity measurements at the designated working sash position. (To pass, the average velocity must be within plus 20% or minus 10% of the design rating at the standard operating sash opening. This is typically 90-120fpm. For most chemical fume hoods at the University, standard operating sash opening is 18 inches sash height, or two panes open on a combination sash hood.)
  • Chemical fume hood alarm

Tested chemical fume hoods will have EHS labels affixed stating the following: test date; initials of inspector, and face velocity readings at the standard operating sash opening as indicated on the test label.

For chemical fume hoods found to be outside of the designated range at the standard operating sash opening, Facilities Services will be contacted for airflow adjustments (this does not apply to low flow chemical fume hoods). EHS will post hoods: “Out of Service/Do Not Use.” Hoods that are posted “Out of Service/Do Not Use” may need to be emptied and cleaned as determined by the EHS Safety Clearance procedure to prevent chemical exposures for lab occupants and personnel who will repair the hood system.

Radiation Chemical Fume Hoods

If a radioactive materials posted hood is above 90 fpm and below 100 fpm, a request for airflow adjustment should be submitted to Facilities Service as soon as practicable. The hood can be continued to be used if below 100 fpm as long as it is posted as “Air flow adjustment has been requested”. If below 90 fpm the hood should not be used for radioactive materials until adjustments are made. EHS will post hoods: “Out of Service/Do Not Use.”

After repairs, EHS or Facilities Services, as appropriate, will perform follow-up testing.

Low Flow Chemical Fume Hoods

Low flow chemical fumehoods are manufactured as low flow hoods. It is designed to be an energy savings fumehood. A low flow hood is one that has had the exhaust volume reduced by operating through a smaller sash opening. This type of hood does not require the containment be the same with the sash full open for setup as it is for usage. Energy savings can parallel that of low velocity hoods, but proper sash position for usage or setup must be managed. These fume hoods will be tested by EHS based on the manufacturers’ criteria.

Biological Safety Cabinets

Responsibility: Users

EHS recommends annual certification for all biosafety cabinets at biosafety level 1 (BSL-1) and BSL-2; however, if the BSL-2 cabinet is used for concentrations of risk group 2 agents, annual certification is required. This includes ducted and non-ducted biosafety cabinets. All biosafety cabinets at BSL-3 are certified annually. Contact EHS at 919-966-5507 to arrange for certification.


Upon request EHS can check the airflow on an existing snorkel. Contact EHS at 919-962-5507.

References and Addendum

Key References

  • ANSI/AIHA Z9.5 (most current)
  • ASHRAE 110 1995 (or most current)
  • NSF/ANSI-49 (most current)
  • UNC EHS Laboratory Design Guidelines (most current)
  • UNC Laboratory Safety Manual (most current)
  • UNC Biological Safety Manual (most current)

Laboratory Ventilation Policy: Addendum 1

Performance Requirements

  1. Follow ASHRAE 110-1995 flow visualization test with low and high volume smoke at designed opening, 18”. Hood should not be
    Pass/Fail Criteria
    Rating Description
    • Smoke was visually observed escaping from the hood
    LOW PASS (Poor)
    • Reverse flow of smoke is evident near opening
    • Lazy flow into hood along openings
    • Slow capture and clearance
    • Observed potential for escape
    PASS (Fair)
    • Some Reverse flow in hood not necessarily at opening
    • Limited turbulent vortex flow inside hood
    • Smoke is captured and clears readily
    • No visible escape
    HIGH PASS (Good)
    • Good capture and quick clearance
    • Limited vortex flow inside hood
    • No reverse flow regions
    • No visible escape
  2. Face Velocity should be 100fpm, +20% or -10% at designed opening (per ANSI 5).
    1. No single point in the face velocity testing may be +/- 20% of the average, at designed opening.
    2. Test face velocity at 50% and 25% of designed opening. At 50% opening, face velocity should be 80-150fpm. At 25% of design opening, face velocity should be 80-300fpm.
  3. Perform ASHRAE 110-1995 tracer gas test at 4Lpm. Results must be less than 0.05ppm.
    1. Vertical hoods should be tested in the right, left, and center positions at designed opening.
    2. For horizontal sashes, test with the maximum opening in the left, right, and center positions
    3. All tracer gas testing should be performed with the hood loaded.
  4. Perform walk-by test with tracer gas with the mannequin in the center position. Execute three rapid walk-bys, 12 inches behind the mannequin, at 30 second intervals. Tracer gas concentration shall not exceed 0.1ppm and should return to specified containment within 15
  5. All testing should be done using the specific diversity factor for at least the section of the floor being tested, if not the entire building, to ensure the total of the fume hood exhaust system is being challenged, as applicable.
  6. Test Fume Hood Alarms
    1. Alarm should activate when hood sash is fully
    2. Alarm reading should match tested face

Contact Information

Policy Contact

Environment, Health and Safety
1120 Estes Drive
Campus Box #1650
Chapel Hill, NC 27599-1650
Phone: 919-962-5507

Back to Chapter 05.18 - Respiratory Protection Program

Proceed to Chapter 05.20 - Clearance of Laboratories Where Hazardous Materials Have Been Used


Article ID: 131973
Thu 4/8/21 9:20 PM
Mon 7/4/22 2:11 PM
Effective Date
If the date on which this document became/becomes enforceable differs from the Origination or Last Revision, this attribute reflects the date on which it is/was enforcable.
01/30/2019 12:00 AM
Issuing Officer
Name of the document Issuing Officer. This is the individual whose organizational authority covers the policy scope and who is primarily responsible for the policy.
Issuing Officer Title
Title of the person who is primarily responsible for issuing this policy.
Executive Director
Last Review
Date on which the most recent document review was completed.
01/30/2019 12:00 AM
Last Revised
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01/30/2019 12:00 AM
Next Review
Date on which the next document review is due.
09/01/2026 12:00 AM
Date on which the original version of this document was first made official.
04/01/2014 12:00 AM
Responsible Unit
School, Department, or other organizational unit issuing this document.
Environment, Health and Safety