Fume Hood Prudent Practices

A chemical fume hood can provide adequate protection for most laboratory processes if they are used correctly. Fume hoods are analyzed and reported on at least every two years to assess performance standards.

The following are some "practical" tips to optimize the protection a fume hood can provide.

For a list of approved fume hoods click here.

  • Is the fume hood functioning? The hood operator should determine whether it is functioning before beginning any work. This can be done with an electronic safety monitor or checking the airflow with a thin strip of paper. If the fume hood is not functioning: stop and cover all reactions, then call Physical Plant, 206.685.1900, immediately.
  • If necessary adjust the hood baffles properly before setting up any work. Most fume hoods have adjustable rear baffles. This controls from where the largest volume of air will be exhausted: the upper, middle, or lower air space. The total air volume exhausted by the hood will not change when adjusting the baffles. Use of heavier than air fumes are best exhausted with the lower baffles opened. Use of fumes lighter than air or when high loads of heated fumes are generated, it is best to exhaust with the upper baffles opened. Some fume hoods have baffles that are not adjustable; instead they are fixed in the most optimal setting for general hood usage.
  • Select proper exhaust speed setting. Some fume hoods have a two speed exhaust fan with a local control at the hood. The LOW or SLOW exhaust setting is designed to provide air exhaust for chemical storage within the hood. The HIGH or FAST exhaust setting provides protection for working with chemicals (e.g. mixing, measuring, pouring, distillations, etc.). Some local controls contain an "OFF" setting which should not be used. The hood should be left running to provide adequate room ventilation along with chemical fume ventilation.

  • Fume hood sash closed
  • Work with the hood sash partially or completely closed. If this is not possible, additional Personal Protective Equipment (PPE) should be used to ensure adequate protection.

  • fume hood from best to good to 
            bad usage
  • Move work at least six inches inside the face of the fume hood. This minimizes the effect of cross-drafts and eddies created by the hood operator or by occupants walking by the hood. Also, keeping windows and doors closed will control cross-drafts.

  • fume hood ventilation
  • Avoid overcrowding the fume hood work areas. Chemicals and equipment not in use should be removed from the hood to a proper storage cabinet. Large bulky equipment used in the hood will cause eddies that can be reduced by making sure there is a 1-2 inch air space on all sides including the bottom. Avoid using equipment that blocks the hood sash from closing. A safer ventilation method may exist and should be pursued.
  • Control reaction rates and observe process until completion. Controlling the rate of vapor and particle formation can minimize the risk of exposure. Never leave a reaction unobserved for an extended period of time, due to possible hood failure or unexpected accidents/spills.
  • Minimize fire hazard within the hood. Do not place electrical spark producing equipment in a hood containing flammable chemicals. Never leave a flame or heating apparatus unattended. No permanent electrical receptacles are permitted inside the hood.
  • Do not attach or insert exhaust ducts or snorkels to the hood without checking with EH&S (206.221.5549) or Campus Operations (206.685.1900). Drilling holes into the side of a hood increases the risk of fume exposure if not done properly. The UW certifies fume hood performance and thus the hood should not be physically altered without prior approval and consent.

For further information and questions, please call EH&S Building and Fire Safety at 206.221.5549.