An effective protection factor study of respirators used by primary lead smelter workers

An industrial hygiene study was conducted at a primary lead smelter to determine the effective protection factors for negative pressure and powered air purifying half-mask respirators. The study involved 99 paired personal samples taken in six different work areas, in which randomly chosen subjects from the workforce wore dual sampling pumps connected to closed-face 37-mm cassettes. The cassettes were attached either to the workers' lapels for exposure measurements outside the respirator or to a ported respirator for exposure measurements inside the respirator. Samples were collected throughout the work shift and analyzed for lead according to National Institute of Occupational Safety and Health (NIOSH) Method 7082. Using particle size distribution data obtained for the same workplaces, the within-mask samples were corrected for sampling bias. The negative pressure half-mask respirators showed a mean effective protection factor of 6.5 and a mean corrected effective protection factor of 4.56, with a 5th percentile less than 0.5. Approximately 80 percent and 90 percent of the effective protection factors and the corrected effective protection factors, respectively, were equal to or less than the assigned protection factor of 10. For the powered air purifying half-mask respirators, the means for effective protection factor and corrected effective protection factor were 18.20 and 11.92, respectively, with a 5th percentile of 1.0 or less. Approximately 90 percent and 95 percent of the effective protection factors and the corrected effective protection factors, respectively, were equal to or less than the assigned protection factor of 50. The uncorrected and corrected within-mask lead concentrations for both types of respirators exceeded the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for lead by 19 percent to 58 percent. These results indicate that the straight application of assigned protection factors to actual workplace situations may not always be appropriate.