In the United States, respirator use in the workplace is regulated by OSHA, and employers allowing or requiring respiratory use must follow the requirements of OSHA’s Respiratory Protection Standard - 29 CFR 1910.134. The standard requires employers to implement a written respiratory protection program with several elements, including provisions for respirator selection, medical evaluations, fit testing and employee training to name a few. In this article we will focus on one element of an effective written program: Fit testing.