The Fundamental Importance of Fit One of the most important criteria for any filtering facepiece air-purifying respirator to be effective is that a good seal is formed between the respirator’s facepiece and the wearer’s skin. The ability to achieve this seal is called the respirator’s fitting characteristic. In 1995, when NIOSH put Title 42 Code of Federal Regulations Part 84 (42CFR84) into operation, it did not include an evaluation of the fitting characteristics of respirators approved only for particulates.1 In addition, no voluntary consensus or other government-unique standards existed to evaluate the fit capability of a filtering facepiece respirator prior
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