A comparison of exposures to refractory ceramic fibres over multiple work shifts

As part of an ongoing, industry-wide study in the manufacture of refractory ceramic fibres (RCF), time weighted average (TWA) exposures have been collected at five facilities according to a standardised protocol. Work activities were grouped into dust zones (DZs). Persons to be sampled were randomly selected according to a protocol designed to assure that at least one sample was collected annually from each DZ; each work shift is also sampled at least annually. TWA exposures calculated over a sampling period of at least 360 min were included in the data set. DZs were combined into one of three groups (DZGs): fibre production; vacuum processes; other. The data were analysed to identify any differences by DZG between airborne fibre exposures, by the shift worked at each facility, and across all facilities. There were no statistically significant shift-related differences detected between airborne fibre exposures across the five RCF facilities when analysed as a group. Within four of the facilities, no shift-related differences were detected between airborne fibre exposures; however, at one facility, first and third shift exposures were statistically different. No documentation related to job activities was found to account for the observation. The data generally support the use of a single exposure estimate for each DZG in each of these facilities, regardless of shift worked. Researchers reconstructing exposure and not able to determine the shift worked by study subjects may find these results useful, but are cautioned that substantial differences in exposure across shifts may exist in other types of manufacturing.