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.
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
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.
To maintain effectiveness and performance and to minimize exposure,
- All operations should be performed at least 6 inches inside the hood
- Avoid rapid movements, such as opening & closing doors, that can create cross-drafts and disrupt airflow
- Keep sash as low as possible. The glass provides a barrier against a spill, splash, or explosion.
- Chemicals and equipment should not be stored permanently inside the hood
- The hood sash or panels must not be removed from the hood or altered.
- Close sash when hood is not in use
- Check the air flow monitor periodically. If the monitor is alarming, do not mute or
use the fume hood. Contact
- Certain chemicals used in large quantities such as perchloric acid, hydrochloric acid, and hydrofluoric acid should not be used in a chemical fume hood that is not approved for their use.
- Radioactive materials should only be used in chemical fume hoods if certified by the Radiation Safety Office.
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.
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:
- Discontinue all operations that may produce hazardous vapors, gases, or dust.
- Securely cap/cover all open chemical containers in the fume hood
- Close fume hood sashes.
- Contact Environmental Health & Safety at 813-974-4036, or Physical Plant at Tampa - 813-974-2845, or fill out a Physical Plant work order request online at http://www.pplant.usf.edu/facnetcustomerweb/. If you are located on the St. Petersburg campus, contact Operations and Maintenance of Facilities at 727-873-4135.
- Do not use the fume hood until it is fully operational
- If hazardous vapors, gases, or dust have entered the room, leave the area immediately, and contact Environmental Health & Safety and/or the University Police.