Correcting Coal Miner Respirator Total Inward Leakage Values for Respiratory Tract Deposition

The great majority of workplace respirator efficacy studies have measured total inward leakage (TIL) for particulate contaminants. One of the first such studies, designated the Harris study, was conducted in the early 1970s in US underground coal mines. As in other particle-based studies, inside-the-facepiece dust sampling was continuously conducted across the inhalation and exhalation phases of the breathing cycle, although unlike in other studies, respirable dust cyclones were used in air sampling. Because exhaled air was partially depleted of dust particles due to deposition in the respiratory tract, the measured time-averaged dust concentration inside the facepiece underestimated the time-averaged dust concentration inspired into the facepiece. In turn, the reported TIL values underestimated the true TIL values experienced, which is to say, overestimated respirator efficacy. This paper describes a method to correct the Harris study's reported TIL values for respiratory tract deposition while accounting for particle size-selective sampling by the cyclone devices. Given the estimated coal mine particle size distribution outside the respirator, it is shown that the reported TIL values should be increased by the multiplicative factor 1.69. This paper also discusses the assigned protection factor (APF) of five for the quartermask respirator class and shows that 4/5 quartermasks in the Harris study did not meet the criterion for complying with this APF value when using the corrected TIL values.