Move work at least six inches inside the face of the fume hood. This minimizes the effect of cross-drafts and eddy currents created by the operator working at the hood or occupants walking by the hood. Adjust the rear baffles properly. On most fume hoods there is an opening at the top of the fume hood and two slot openings at the back center and work surface. Make sure you select the proper exhaust speed setting.
Some fume hoods have a two speed exhaust fan with local control at the hood.
Check processes and procedures along with the fume hood velocity label posted on the fume hood to assure that adequate personal protection is provided. Labels and decals are placed on the face of each fume hood indicating the measured velocity and optimum face velocity position. The optimum face velocity is 100 Linear Feet Per Minute and its location is marked with a decal arrow. This mark is not necessarily where the sash should be located when using a fume hood. Always work with the sash partially or completely closed as this provides the best overall protection for the user.