C. Hazardous Face-Seal Leakage—A proper seal between a respirator's sealing surface and a wearer's face is absolutely essential for effective and reliable performance of any respirator with negative pressure inside the facepiece. It is much less critical, but still important, for a positive-pressure respirator. Hazardous face-seal leakage can result from factors such as incorrect facepiece size or shape, incorrect or defective facepiece sealing-lip, beard growth on a wearer, perspiration or facial oils that can result in facepiece slippage, user failure to use all the headstraps, incorrect positioning of a facepiece on a wearer's face, incorrect headstrap tension or position, improper mask maintenance, and mask damage.
To assure an adequate seal, quantitative fit tests must be performed periodically and accurately to detect face-seal leakage. Fit tests help ensure that a respirator can provide adequate protection on each wearer and that it is fitted properly to each wearer's face. However, fit tests can detect only the hazardous face-seal leakage that exists at the time of the fit testing. Also, fit tests do not detect hazardous leakage through the filter.
An additional benefit of quantitative fit tests is that the screening cutoff value in these fit tests can be adjusted to assure very low face-seal leakage considerably less than 2% (81,82). For example, when quantitatively fit testing, NIOSH uses a screening value of 0.2% leakage for the non-powered operational mode of powered, HEPA-filter, halfmask respirators to assure less than 2% leakage in the powered mode of these respirators.
Because point-of-use factors can create a considerable risk of undetected hazardous leakage past a face seal when a respirator is worn in a hazardous environment, each wearer must have the capability of effectively and reliably fit checking his or her respirator for proper fit before every respirator use. This is the purpose of fit checks that must be performed by users each time they don their respirator. The rationale for and the essential nature of both fit tests and fit checks are summarized in Table 1 on page 20.
