Western Carolina University

Chemical fume hoods are the primary containment device in the laboratory used to control airborne contaminants generated by experimental procedures. Chemical fume hoods provide personnel protection by means of directional airflow from the laboratory into the hood through the face opening. This airflow reduces the potential for escape of airborne contaminants into the laboratory. Procedures involving volatile chemicals and those involving solids or liquids that may result in the generation of toxic vapors should be conducted in a chemical fume hood rather than on the open bench. Placing a reacting chemical system within a hood, especially with the hood sash closed, places a physical barrier between the workers in the laboratory and the chemical reaction. This barrier can afford laboratory workers protection from chemical splash, sprays, fires, and minor explosions. Hoods should be evaluated before use to ensure adequate face velocities. Hoods are checked by the Safety & Risk Management Office to determine the face velocity.  An adequate face velocity for most applications is 100 feet per minute + / - 10%.  Hoods with low face velocity <75 feet per minute are posted as "low toxic only" use.  Although chemical fume hoods do protect laboratory personnel from exposures to hazardous materials, they must be used properly in order to maximize their effectiveness.  The following practices should therefore be observed when using fume hoods:

• Hood work areas should be clear of unnecessary equipment and materials, which can disrupt airflow and block, vents. Hoods should not be used for storage of chemicals.
• Work should be carried out as far back in the hood as possible.  Moving apparatus 10 cm back from the front edge can improve performance by 90%.
• Experiments should be planned so that, as much as possible, all of the materials needed for a procedure are present in the hood to eliminate disruption of airflow by carrying equipment in and out during a procedure.
• Disruptive room air currents should be minimized by avoiding traffic near fume hoods and opening and closing doors near fume hoods while experiments are in progress.
• Keep the sash as low as possible.
• Use equipment with legs, if possible.
• Adjust the inside baffle at back of the hood so the bottom slot is wide open and the one at the top is closed or partially closed.  This will favor airflow across the workbench where heavier than air solvent vapors congregate.

Safety Training Video: Fume Hood Operation