Fume Hoods: Procedures and Practices
- Equipment Use
- Good Work Practices
- Waste Disposal
- Good Housekeeping Practices
- Proper Sash Use
- Fume Hood Testing and Maintenance
Laboratory fume hoods serve to control exposure to toxic, offensive or flammable vapors, gases and aerosols. Fume hoods are the primary method of exposure control in the laboratory.
Use the right hood for the job:
- General Purpose Hoods:
- Standard Fume Hood
- Bypass Hood, or Constant Volume Hood
- Variable Air Volume (VAV) Hood
- Auxiliary Air Supplied Hood (Note: At UWM, found only in the Chemistry Building)
- Radioisotope Hood--These hoods have been authorized by Radiation Safety for use with volatile radioactive materials.
- Biosafety Cabinet--Specialized hoods to prevent or minimize the exposure of humans or the environment to biohazardous agents or materials.
- Perchloric Acid Hoods must be used when working with PCA (e.g., acid digestion procedures). These hoods prevent the formation of perchlorates which could lead to explosions. They are constructed with special materials and have water-wash capability.
Hoods are labeled for special use when practical.
- Place apparatus and equipment as far back as possible in hood for safety and optimal performance. Equipment should be placed a minimum of 8 inches inside the hood. Keep electrical connections outside of hood.
- Ensure that equipment or materials do not block the baffle vents in the back of the hood.
- When using a large apparatus inside the hood, place the equipment on blocks, when safe and practical, to allow air flow beneath it.
- Do not place electrical apparatus or other ignition sources inside the hood when flammable liquids or gases are present. Keep in mind that liquids with low flash points may ignite if they are near heat sources such as hot plates or steam lines.
- When using the fume hood, keep your face outside the plane of the hood sash and remain alert to changes in air flow.
- Work at least 6 inches back from the face of the hood. A stripe on the bench surface is a good reminder.
- Always use splash goggles, and wear a full faceshield if there is possibility of an explosion or eruption.
- Do not make quick motions into or out of the hood, use fans, or walk quickly by the hood opening. All will cause airflow disturbances which reduce the effectiveness of the hood. A demonstration of the effects of walking past the fumehood is demonstrated in this video clip from the EHS Department at the University of Nevada-Reno.
- Substitute less hazardous or less volatile chemicals where possible;
- Look for process changes that improve safety and reduce losses to the environment (e.g. more accurate chemical delivery systems vs. pouring volatile chemicals from bottles); and,
- Develop a process to evaluate research proposals ahead of time for potential emissions and look for opportunities to reduce them.
Do not use the hood as a waste disposal mechanism. Apparatus used in a hood should be fitted with condensers, traps, or scrubbers to contain and collect waste solvents, toxic vapors or dust. Please contact staff in UWM's Hazardous Waste Program for additional information on waste disposal or refer to the following webpage: Hazardous Waste Disposal Information.
- Limit chemical storage in fume hoods. Keep the smallest amount of chemicals in the hood needed to conduct the procedure at hand;
- Store hazardous chemicals such as flammable liquids in an approved safety cabinet;
- Keep caps on chemical reagent bottles tight and check fitting on laboratory glassware to minimize vapor loss;
Always use good housekeeping techniques to maintain the hood at optimal performance levels. Excessive storage of materials or equipment can cause eddy currents or reverse flow resulting in contaminants escaping from the hood.
- Do not remove sashes from sliding sash hoods. The hood should be kept closed, except when working within the hood is necessary.
- Use sliding sash for partial protection during hazardous work.
- Do not remove the sash or panels except when necessary for apparatus set-up. Replace sash or panels before operating.
- Keep the slots of the hood baffles free of obstruction by apparatus or containers. See video clip (courtesy of University of Nevada EHS Department.)
- Keep the hood sash closed as much as possible to maximize the hood's performance. Keep the sash closed when not in use to maximize energy conservation. This video clip (courtesy of the University of Nevada) demonstrates the effects of raising and lowering the sash height.
Demonstration of fume hood capture efficiency with the sash in the full-open position. Notice escape of the visualization smoke from the bottom of the hood.
Notice the improved capture efficiency with the sash in the partially-closed position.
Hoods should be evaluated by the user before each use to ensure adequate face velocities and the absence of excessive turbulence.
In case of exhaust system failure while using a hood, shut off all services and accessories and lower the sash completely. Leave the area immediately.
The required face velocity is 100 feet per minute (0.5 m/sec). This velocity is capable of controlling most low-velocity cross drafts and turbulence created by normal working practices at the face of the hood. All hoods should have a sticker designating the maximum safe sash height. Keep the sash at the appropriate level to ensure optimal face velocity.
The low flow hoods in the North Tower of the Chemistry Building were evaluated at installation using the ASHRAE 110 Method of Testing Performance of Laboratory Fume Hoods. In this sophisticated test, a tracer gas (sulfur hexaflouride) is released at a known rate inside the hood. Samples are taken in the breathing zone of a mannequin standing at different positions in front of the hood. The DILHR mandated pass criteria is 100 parts per billion (ppb) tracer at the breathing zone of the mannequin. As with conventional style hoods, keep the sash at the appropriate level as indicated by the test label to ensure optimal hood performance. The objective is to minimize the sash opening to achieve proper containment.
Regular testing of the fume hood should be done by Facility Services or University Safety and Assurances staff to ensure that it is operating properly. Hoods are labeled to indicate the last inspection date. If your hood has not been tested within the past year, please contact Zack Steuerwald, x5808.
State of Wisconsin Department of Safety and Professional Services states :
(6) VENTILATION FOR LABORATORY FUME HOODS.
The OSHA Laboratory Standard (29 CFR 1910.1450) does not specify safe hood operation, flows or face velocities. However, it does mandate a chemical hygiene plan and lists requirements for the plan, including "a requirement that fume hoods and other protective equipment are functioning properly and specific measures that shall be taken to ensure proper and adequate performance of such equipment." The non-mandatory Appendix A states: "General air flow should not be turbulent and should be relatively uniform throughout the laboratory, with no high velocity or static areas; airflow into and within the hood should not be excessively turbulent (200); hood face velocity should be adequate (typically 60-100 lfm)"