ABSTRACT
The term “protection factor” (PF) was first defined by the Bureau of Mines in the respirator Approval Schedule 21B in 1965. 1 The PF is a measure of the degree of protection provided by the respiratory protective device during use and is defined as the ratio of the concentration of airborne radioactive material outside the respirator to that inside the facepiece. Half-mask air-purifying respirators equipped with high-efficiency particulate air (HEPA) filters were approved for a PF of 10, i.e., it can be used up to 10 times the threshold limit value (TLV) of the air contaminant. The full facepiece air-purifying respirator equipped with HEPA filters were approved with a PF of 100 (100 × TLV). The PFs for these devices were determined from quantitative fit testing (QNFT) using dioctyl phthalate (DOP) or di-2-ethylhexyl phthalate (DEHP) aerosol with six male test subjects performing simulated work exercises.
