Quantitative fit testing techniques and regulations for tight-fitting respirators: current methods measuring aerosol or air leakage, and new developments.

Until a few years ago, only two quantitative fit testing (QNFT) techniques were available and accepted by U.S. Occupational Safety and Health Administration (OSHA) regulations. In the 1980s and 1990s, several new and fundamentally different QNFT methods were developed. Two of the newer methods are commercially available and are accepted by OSHA as suitable alternatives. In this article the principles of operation of the OSHA-accepted and of some newly developed but not yet approved QNFT techniques are explained, and each technique's major advantages and disadvantages are pointed out. Emphasis is given to negative-pressure air-purifying respirators, as they are in most frequent use today. The requirements and recommendations for fit testing positive-pressure respirators are discussed as well. Finally, the presently available QNFT standards and regulations are summarized to assist the user in making fit testing decisions.