Fume Hoods

Laboratory fume hoods are designed to protect laboratory users from exposure to hazardous materials. Fume hoods provide a safe, enclosed work area for chemical manipulations and provide critical ventilation for the user and laboratory. This ventilation is often the best engineering control available to keep chemical exposure below exposure limits. Proper fume hood use also assists with containing spills, providing shielding, removing odors, and reducing the concentration of flammable vapors.

Fume Hood Use

It is good work practice to use a fume hood whenever possible as a protective measure. Fume hoods should always be used when working with or potentially producing a substance that has a threshold limit value *(TLV) of less than 50 ppm. The TLV for a substance will be listed on the Safety Data Sheet (SDS). Fume hoods are typically the best method of protection when working with flammables, corrosives, water reactive chemicals, and pyrophoric materials as well.

Using a Fume Hood

All fume hood users should take Fume Hood Training to properly understand the elements of a hood and to learn about proper fume hood use. Some key points to fume hood use are below.

• The fume hood sash should be opened only as far as necessary to access your work. Always keep fume hood sash closed when the hood is not being used (see Drawing A) 
• Do not store excess chemicals or equipment in a fume hood. Contact Chemical Safety if you need to use large pieces of equipment inside of a hood.

Avoid making rapid movements while working in a fume hood and avoid walking close to a fume hood that is being used by a coworker. The air current disturbance may cause erratic air flow endangering yourself or a coworker.

• Place chemical sources and apparatus at least 6 inches behind the face of the hood. Do not lean into the hood while working with hazardous chemicals. This negates the protection the hood provides.
• Run all electrical cords underneath the hood airfoil, along the front edge of the fume hood, to external electrical outlets. In an emergency the sash can be closed completely, and cords can be unplugged without reaching into the hood or creating the potential for sparks inside the hood.
• Do not modify fume hoods in any way without consulting with Physical Plant or EH&S. This includes adding, removing, or changing any of the fume hood components, such as baffles, sashes, airfoils, liners, and exhaust connections.

All fume hoods have a face air velocity indicator which will alarm if there is a loss of airflow. If the alarm sounds, stop operations, seal all containers, and close sash fully. Contact Physical Plant if the problem persists.

• Ductless fume hoods are NOT permitted at the University of Wisconsin–Madison.
• Biosafety cabinets, Laminar flow clean benches, Pharmacy Isolators, and Glove boxes are NOT fume hoods and DO NOT provide the same protections.

Specialty Fume Hoods

Not all hoods may be used for all chemicals. Some chemicals require specially designed and designated hoods.

• The use of high concentrations of or any operation evaporating perchloric acid fumes require a perchloric acid fume hood. These hoods have a water spray system to wash down the entire length of the exhaust duct, the baffle and the wall to remove any perchloric acid or organic material that may have accumulated.
• Hydrofluoric acid (HF) fume hoods must be specifically designed to be resistant. An example of this is HF hoods have lexan^tm Sashes which prevent fogging of the sash, and HF hoods also are being produced out of none metallic materials.

Fume hoods with motion sensors (Inactive Set back mode hoods)

Inactive setback mode is an energy saving measure that minimizes the hood’s air flow when the hood is not in use. You can identify if your hood has inactive set back mode by the presence of a motion sensor directly over the hood (See Figure C).

• The hood will go into set back if the motion sensor does not see movement for 2 minutes.
• When your hood goes to inactive set back the face velocity slows to a point that is safe with sash fully closed
• If the hood goes to inactive set back mode with sash panels open an audible alarm will sound and a warning light will turn red on the face velocity meter.
• To stop alarm from sounding shut the sash or move in front of the motion sensor causing it to go back to normal operation mode.

What to do if your fume hood is not working or stays in alarm

• Contact Physical Plant Customer Service at 608-263-3333 for repairs.
• If you have concerns about how to use your fume hood properly or how to handle materials in your fume hood contact Chemical Safety at 608-265-5700.