How to Use Chemical Fume Hoods

When used properly, chemical fume hoods provide superlative protection when you work with flammable, explosive and corrosive materials. However, training on the correct technique for use of chemical fume hoods is commonly lacking for novice laboratory technicians and scientists. A chemical fume hood works by providing a negative air pressure environment in front of the operator, constantly pulling room air into the hood and exhausting it up and out of the building. The basic steps for ideal operation are fairly universal, and while there are decent guidelines available, this article covers the practical measures to take when you perform a procedure that requires the use of a standard chemical fume hood with a vertical sash.

Things You'll Need

• A Chemical Fume Hood not in use by other personnel.

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Instructions

• 1

  To prepare the chemical fume hood for use, turn on the light and open the vertical window sash no more than 18 inches (many have a safety stop). Determine that the hood has been certified for use in the past year by noting any inspection stickers with dates. Check any available Fume Hood Flow Monitors for indications that the hood is functioning properly. Sometimes the hood will be drawing air in at too low a rate to provide adequate protection; terminate the procedure and seek consultation if there is any doubt about the proper functioning of the unit.

• 2

  Ensure that any baffle operational controls are set to Normal General Procedures. The baffles control air flow and are located in the back of the hood. The baffle contol lever, if present, will be labeled as such on the front of the hood. The vast majority of procedures require exhaust with the baffles set to "Normal"; more complicated procedures require users who are experts at fume hood use.

• 3

  Gather all equipment and materials that will be used in the procedure, excluding exceedingly bulky items that may disrupt air flow. Place everything as far back into the hood as possible; consider the first six inches of the interior work surface a "no work zone." Raise any low profile items one to two inches off the surface of the hood using rubber stoppers or the like without posing an inadvertent safety risk.

• 4

  If any equipment requires an electrical cord, first note that the electrical outlets will be exclusively located on the outside of the hood to prevent any sparking and subsequent fires or explosions within. This means absolutely no extension cords should be run inside the hood! Also note that the outlets are sometimes of low amperage (20 amps) compared to other laboratory power supplies, meaning the use of high power instruments may trip the circuit breaker. If possible, run all cords under the airfoil on the front lip of the hood to prevent any air turbulence.

• 5

  Lower the vertical sash so that there is enough room to fit your arms through and perform the procedure. The sash acts as a barrier to possible splashes and, if made of safety glass, can provide some protection against catastrophic events. Minimize side-to-side movements and constant in-and-outs. This is again to prevent any undesired and deleterious air turbulence that put you at risk for exposure to the agents you are manipulating.

• 6

  When you are done with your tasks, remove all the equipment and items that were introduced into the hood, properly clean the interior and turn off the interior light. Close the sash to the mandated height: some institutions rely on continuous hood function to keep the entire laboratory under negative pressure; others have separate means for negative pressure maintenance and save electricity by lowering the sash all of the way. Check with the building contractor or the safety office for compliance.