Chemical Fume Hoods

A fume hood is an enclosure that minimizes exposure to airborne chemical contaminants (chemical vapors not biologicals). There are three different types of chemical fume hoods used on campus. They are general purpose hoods, radioactive material hoods, and perchloric acid hoods.

General Purpose Hoods are to be used only for the removal of vapors released by chemicals or generated by chemical reactions involving acids (not heated), organic solvents, and radioactive materials within Nuclear Regulatory Commission (NRC) guidelines. Do not handle perchloric acid, hot concentrated acids, highly toxic materials, unstable chemicals or explosives, or radioisotopes exceeding NRC guidelines.

Radioactive Material Hoods are to be used where radioisotopes are handled (NRC guidelines). Do not use hot perchloric acid, hot concentrated acids, unstable or explosive materials in this type of hood. Do not use radioactive material hoods for routine use of perchloric acid.

Perchloric Acid Hoods are to be used when handling hot perchloric acid, hot nitric acid, or for routine use of perchloric acid. Do not handle sulfuric acid, acetic acid, organic solvents, or any combustible materials in perchloric acid hoods. Make sure that you know how to operate the wash down systems in these hoods. Wash down systems need to be used after any operation in the hood.

 

  Fume Hood Operation Procedures

1. Located on your fume hood should be a posting of the hood's face velocity. This is the average velocity of air that is carried across the face of the fume hood (measured in feet per minute, fpm). Prior to using the fume hood, check this posting to make sure that the hood is working properly. The face velocity should be from 100 to 120 fpm. If a CAUTION or DANGER sign is posted, do not work in the hood until the face velocity has been adjusted. Contact Environmental Safety on campus at 542-5801 concerning the proper functioning of your fume hood.



2. Foot traffic, local ventilation systems, windows and doors may cause air currents to form across the face of the hood which may reduce the hood's performance by pulling air out of the face of the hood into the breathing zone. Therefore, make sure that doors and windows are kept closed when hoods are in operation. Foot traffic and rapid arm/body movement should be avoided. A person walking in front of the hood can create a velocity of 250 fpm. Velocities from the local air systems may exceed 800 fpm. These velocities greatly exceed the average face velocity of a hood which generally ranges between 100-120 fpm (therefore result in a pull of air from outside the hood).
   


3. Place chemical sources and equipment at least 6 inches behind the face of the hood. Applying tape across the work surface at the 6 inch line will help as a reminder. Studies have shown that contaminants may be 300 times greater if work is performed at the face of the hood than at this 6 inch mark. Do not extend your head inside of the hood while experiments are being performed.
   
   
4. Perform work with the sash height at 10-12 inches, otherwise the sash should remain closed and the hood should remain on. Labeling these marks on the outer frame of the sash will also provide a reminder to workers.
   
   
5. Large pieces of equipment in the hood may cause dead space and should not be used in the hood. Large pieces of equipment such as a GC's that emit gases/fumes should have special purpose hoods or other ventilation devices designed for there specific use. Keep fume hoods and adjacent work areas clean since solid debris can enter the hood's exhaust duct work.
   
   
6. When handling electrical equipment in a hood take extra precautions. Protect spark sources from flammable vapors. Permanent electrical receptacles are not permitted in the hood.
   
   
7. Handle perchloric acid and nitric acid in a Perchloric Acid Fume Hood only. Wash down systems must be in effective working condition at all times. If there is ever a doubt as to whether the wash down system is functioning properly, stop all reactions and call the maintenance shop to have it fixed. Any other operation other than those which use nitric and perchloric acid should be prohibited due to the reactive nature of these two chemicals. Contact Environmental Safety Services on campus at 542-5801 if you have any questions concerning perchloric acid fume hoods.
   
   
8. Do not cut holes into the hood or it's duct work since they may adversely affect the performance of the hood. Any opening for which the hood was not specifically designed may lower it's flow to unsafe levels.
   
   
9. Do not store chemicals in a fume hood unless storage is the sole use of the hood. Only those chemicals necessary to perform the experiment should be left in the hood.
   
   
10. Never use hood evaporation as a means of chemical disposal