This testimony concerns NIOSH's analysis of the proposed qualitative screening tests to be used in assessing fit factors of respirators. NIOSH believes that, in order to best protect workers who must rely upon respirators for health protection, a conservative approach must be used for the analysis of available data. The fundamental purpose of fit testing is to identify those prospective wearers who have unacceptable fit factors, so that the proper respirators that produce acceptable protection will be identified. For face fit testing with either the qualitative or quantitative approach, the screening level defines the acceptable and unacceptable fit factors for prospective respirator wearers. NIOSH believes that the OSHA lead standard clearly mandates that time weighted average workplace protection factors of at least 10 for half masks and 50 for full face respirators must be achieved by an employer's respiratory protection program for each individual respirator wearer. The use of the 3M Company saccharin, the Du Pont isoamyl-acetate and the irritant smoke screening tests is discussed. When trying to achieve a high probability of attaining mandated time weighted average working protection factors in the workplace, NIOSH believes that a scale down factor must be applied to fit factors obtained during quantitative fit tests.