Chapter 12: Laboratory Ventilation
Use of Laboratory Hoods
General laboratory room ventilation is designed to provide heating and cooling to the laboratory. General room ventilation does not effectively control personnel exposures to hazardous levels of airborne chemicals. Consequently, laboratory hoods are required to contain chemical vapors and gases at the emission source. Laboratory hoods are the most important control for protecting laboratory workers from chemical exposure.
All chemicals, especially toxic and/or flammable chemicals, should be handled in a laboratory hood whenever it is reasonable to do so. Chemicals that have high acute toxicity or which are carcinogens or reproductive toxins must be handled in a laboratory hood, except for situations where the risk is low (such as operations involving very small quantities or very low likelihood of inhalation exposure). As a general guide, chemicals meeting the definition of “toxic,” or which have an exposure limit less than 50 ppm (or 0.25 mg/m3 for airborne particulate), should be used in a laboratory hood or other containment device that effectively controls exposures.
Guidelines for Laboratory Hood Users
Laboratory hoods are designed to contain vapor and gases; however, the hood airflow must compete against external air currents and turbulent internal airflow in order to achieve effective containment. The following guidelines are good practices that will facilitate effective containment of contaminants.
- Verify sufficient inward airflow before using a hood.
- For hoods with an air velocity monitor, check the monitor. Alternatively, a strip of lightweight paper (such as a Kimwipe) or a piece of yarn should be readily pulled inward when held at the face of the hood.
- Operations that involve heating or volatilizing perchloric acid must be conducted in special perchloric acid hoods. These hoods contain water spray systems to wash down the interior of the hood, ducting, fan, and exhaust stack to prevent accumulation of explosive perchlorate crystalline material. Currently there are no approved perchloric acids hoods on the UNR campus.
- When possible, position the hood sash such that the glass is between the worker (especially the face) and the chemical source. Close the hood sash when not working in the hood.
- Avoid rapid movements at the face of the hood, as they tend to create competing air currents and reduce the ability of the hood to contain air contaminants.
- Keep chemical sources and equipment at least six inches behind the face of the hood.
- Minimize equipment placed in the hood to avoid dead air spaces and/or eddies.
- Equipment used in hoods should be placed on blocks to allow air to flow under and around the equipment.
Evaluation of Laboratory Hood Performance
EH&S performs laboratory hood evaluations to ensure that ventilation performance measures are being met. This normally consists of a face velocity measurement and a visual evaluation of the hood’s ability to capture and contain visual smoke.
- EH&S performs laboratory hood performance evaluations at least on an annual basis.
- Laboratory hood performance should also be evaluated following any maintenance, repair, or modification that could affect ventilation performance.
- After each successful hood performance evaluation a sticker with a red arrow on it is affixed at the side of the hood opening corresponding to a sash height of 16”. This sticker lists the average face velocity of that hood and the date when the next evaluation is due.
- If the hood evaluation indicates that the hood ventilation is not adequate a “Do Not Use” sticker is placed on the front of the sash and EH&S will submit a work request for repair of the hood. Do not use a hood that has been labeled as “Do Not Use.”
- If a laboratory hood has not been evaluated within the past 12 months (or if the due date is within less than a month) contact the CHO or the EH&S Dept. to request an evaluation of the hood.
- A face velocity of 80-120 fpm is recommended for most laboratory hoods. A face velocity outside of this recommended range should be approved for specific use by EH&S.
- Consult with EH&S and Facilities Maintenance before making any change to a ventilation system (laboratory hood or general room ventilation), or for assistance with unique experimental set-ups.
- Do not use lab hoods to "dispose" of chemicals by evaporation unless the vapors are trapped and recovered for proper waste disposal.
Repair and Maintenance of Laboratory Hoods
- If a laboratory hood or other laboratory ventilation device is operating but does not seem to have adequate or normal air flow, call the Chemical Hygiene Officer or call the EH&S Department at (775) 327-5040 and request an evaluation.
- Also notify the Chemical Hygiene Officer or call the EH&S Department if a laboratory hood or other laboratory ventilation device is inoperable or needs repair (e.g., a broken sash).
Laboratory Hood Failure
In the event of a hood failure during chemical use:
- Turn off power to all apparatus in the hood.
- Stabilize the chemical source as much as possible to minimize release. Cover chemical containers if it is safe to do so (do not cover containers that may develop internal pressure).
- Close hood sash.
- Notify other occupants of the laboratory.
- Notify the laboratory supervisor and/or the department office and call Facilities Maintenance at 784-8020 to report the problem. Also report the issue to the EH&S Department by calling (775) 327-5040.
- If hazardous chemicals are released from the hood in a quantity that presents an immediate fire hazard or high health hazard, evacuate the area and call Reno City emergency responders at 911. Call EH&S at (775) 327-5040 (24 hour contact number) if the released material presents a lower risk scenario (no fire hazard and/or lower health hazard). See Chapter 19 for additional information on emergency response actions.
- UNR Ventilation Program – contains information on topics related to laboratory ventilation, as well as video clips that demonstrate loss of hood containment.
- See the University's guide to Laboratory Ventilation for additional information on types of laboratory hoods and biological safety cabinets (BSCs), laboratory hood and BSC performance, and safe work practices.
- UNR Biosafety Manual – Chapter 8 contains information on biological safety cabinets.