What is a fit test? According to OSHA, “a ‘fit test’ tests the seal between the N95 mask’s, or respirator’s, facepiece and your face.” It typically takes 15-20 minutes to complete and should be performed when this type of mask is first used and then at least annually. The purpose of the fit test is to assure that the mask fits and seals properly so potentially contaminated air cannot leak into the mask and so hazardous substances are kept out.
Source: American Dental Association