The assigned protection factor of 10 for half-mask respirators

A number of researchers have published or presented papers on workplace protection factor (WPF) studies involving halfmask respirators. Individually, each study contains a relatively small amount of data, generally less than 25 data points for any single respirator. Because of the small amount of data, any attempt to quantify the result statistically does not provide useful information on the low end of the distribution of WPFs. Several studies on half-mask respirators were combined to yield a data set with 390 observations. Of these WPF data, 1.5% were less than 10, the best estimate of the 5th percentile was 13, with a 95% confidence interval of 10 to 18. Differences between the mean WPF based on the type of filter were found, but no difference was found between the mean performance of elastomeric and disposable respirators equipped with dust/mist and dust/fume/mist filters.