Abstract
The Occupational Safety and Health Administration (OSHA) is promulgating new health standards in which quantitative respirator fitting is required. However, there has been controversy and confusion in the past few years regarding respirator fitting methods and their effectiveness. Members of the Lawrence Livermore National Laboratory's Hazards Control Department employ a quantitative chamber to fit facepieces to users of respiratory protective devices. We are reporting the results of a study to determine the variability in protection factors obtained for multiple facepiece fittings with particular emphasis on the protection fail/pass limits. On the basis of this work, the following statistical statements can be made regarding the protection that would be afforded by a facepiece properly fitted to the user: (1) The probability density function for the fit obtained by one individual wearer with a given facepiece is well-described by a log-normal distribution. (2) The geometric standard deviation for the above distribution varies widely among individuals and facepieces, making it necessary to measure it for each wearer/facepiece combination. (3) A risk plot method can be used to calculate the exposure risk to a wearer.