F. Ventilation

F1. General

Laboratory air should be replaced continuously (8 air changes/ hour). General ventilation provides only modest protection against toxic gases, aerosols, vapors and dusts. General ventilation will not be used for protection against toxins.

F2. Local

Local ventilation will be used to prevent harmful fumes, mists, dusts, gases, and vapors from entering the laboratory air. Your best protection is the chemical fume hood, if used properly.

Fume hoods will be inspected and validated annually by a contractor. Fume hoods will have a face velocity of at least 100 linear feet per minute with the sash in the fully opened position or at the sash catch position. If 100 fpm cannot be achieved with the sash fully open, the sash will be lowered until the face velocity is 100 fpm. The sash will be marked at this position. Each hood used for chemical operations will be labeled with the face velocity and the date certified. The sticker will be placed on the front of the hood above the face opening. See also our Chemical Fume Hood Validation Program.

A simple visible test for users to ensure flow into fume hoods and other ventilation equipment is to tape a telltale to the hood and note its movement. Green telltales have been placed on the left hand side of each sash of each hood in the division.

Experiments or work with highly toxic substances (LD₅₀ <5 mg/kg oral, <40 mg/kg skin, <1000 ppm, <500 mg/m³) may require more specialized local ventilation such as the use of a glove box or other closed system.

F3. Work Practices for Chemical Fume Hoods

• Set up work at least 6 inches from the face of the hood to avoid turbulence at the sash edge
• Separate and elevate each instrument by using blocks or rack so that air can flow easily around all apparatus.
• Do not clutter the hood with unnecessary bottles or equipment. Do not use the hood for storage of chemicals or other materials if it is used for chemical operations as well. Only materials in use should be in the hood.
• Work with the sash in the lowest possible position. The sash provides a physical barrier to protect against splashes, sprays, fires, or minor explosions. Lower the sash completely when no one is working in the hood.
• Do not obstruct the slots at the back of the hood. Keep the hood baffles free of obstructions.
• Do not dismantle or modify the physical structure of your hood or exhaust system in any way without first consulting B&G personnel.
• Do not place electrical receptacles or other spark producing equipment inside the hood.
• Never put your head inside an operating hood to check an experiment. The plane of the sash is the barrier between contaminated and uncontaminated air.
• Clean up spills as soon as possible.
• Do not use a hood for evaporation of chemical wastes.
• Heating of perchloric acid will only be done in a perchloric acid fume hood.

If you suspect that your fume hood is not functioning properly, let the Environmental Health and Safety Coordinator or Buildings and Grounds know.

An 8.5 inch by 5.5 inch Work Practices Guide For Your Fume Hood card is available from the Environmental Health and Safety Office. A copy has been placed in the lower left hand corner of each sash on each hood in the division.

Last modified: April 08, 1998