Variability in protection afforded by half-mask respirators against styrene exposure in the field

Concentrations of styrene were measured in the breathing zone and inside the facepiece of air-purifying half-mask respirators of 13 workers for three to six 1-hr periods while they were engaged in the production of fiberglass-reinforced products. These data were used to estimate the protection afforded by the respirators. In arriving at these estimates, it was necessary to correct the concentration measured inside the mask for pulmonary retention of styrene by the workers. Workers were classified as sprayers or as other production line workers not directly carrying out spraying operations. An analysis of variance showed no evidence of differences in the level of protection afforded by the respirators between the two job classes. A second analysis of variance showed that protection varied between workers as well as for a single worker during different wearing periods. The geometric standard deviation (GSD) between workers was 1.92, the common within-worker GSD was 2.93, and the total GSD was 3.51. One-half of a population of wearers with similar protection would be expected to experience long-term average workplace protection factors in excess of 44 and one-half below that value. The observation of between-worker and within-worker variability in protection indicates that both sources of variability have to be taken into account in the specification of maximum use concentrations.