Laboratory Safety

Fume Hoods

Chemical fume hoods are the  most essential engineering control in a lab. They provide users with  protection against vapors, gases, or dusts given off by hazardous  materials used in the lab. Although there are various types of fume hoods used  at the University of South Florida, general  guidelines should be followed to help maintain the fume hood's performance.

Types of Fume Hoods

Bypass - This type of hood has a bypass mechanism located above the sash face opening that limits an increase of the face velocity as the sash is lowered at or near the closed position. The face velocity remains unchanged when the sash is fully closed.

Bypass Fume Hood Bypass Fume Hood.

Conventional/Constant Air Volume - This is the most commonly used fume hood in our laboratories. The amount of exhausted air remains constant when the sash is in a full open position. As the sash is lowered, the  face velocity increases.

Floor-Mounted - This type of hood is used when a large amount of working space is needed or when large or tall apparatus are being used. One should never walk into a floor mounted fume hood while in operation and containing hazardous materials unless proper personal protective equipment is worn.

Perchloric Acid - This type of hood is designed specifically for the use of perchloric acid. Perchloric acid vaporizes
when heated above ambient temperatures. This can create explosive perchlorate crystals to form within the ductwork of a conventional fume hood. A perchloric acid hood is constructed with materials such as glass, plastic, or stainless steel that are compatible with perchloric acid and its byproducts . It is equipped with a special water wash down system that removes the perchlorate crystals from all interior surfaces, including the ducts, fans, and stack. The system should be activated when heating or using large amounts of perchloric acid to minimize chemical exposure hazards.

Conventional, Walk-in, and Perchloric Acid Fume Hoods Conventional (left), Floor-Mounted/Walk-in (middle), Perchloric Acid (right)


To maintain effectiveness  and performance and to minimize exposure,

Fume Hood Test Schedule

Fume hoods are tested annually by Environmental Health & Safety to ensure  that they are performing within the specifications to protect its users.

          Building                            Month

ISA January
BSF/MDC/MDT February
None June
STG/URL/DAV September
SCA November
None December



Never assume your hood is functioning properly. Always check your hood prior to use. Fume hood exhaust fans may shut down due to an unexpected power failure, equipment malfunction, or other unforeseen events. The following steps should be taken to prevent exposure hazards if your hood is not functioning properly: