The use of compliance monitoring for assessing quarry workers’ exposures to respirable dust and quartz

As part of an epidemiological study of the health of workers in 74 Scottish hard rock quarries we are estimating workers’ exposures to respirable dust and quartz. Respirable dust and quartz concentrations have recently been measured at each quarry in the course of routine compliance monitoring under the Health and Safety Executive’s (HSE) Scottish Quarry Owners Scheme for Respirable Dust and Quartz, over 300 surveys at 85 quarries have been completed and over 1700 samples collected. The validity of using these measurements for exposure monitoring has been investigated by carrying out a series of detailed surveys at four of the quarries. Three 1-week long surveys have been carried out at each quarry, one each in winter, summer and spring or autumn. In both the compliance monitoring surveys and the research studies respirable dust and quartz levels differed substantially between quarries and between occupations within quarries. For most occupations the proportions of quartz observed in dust clearly depended on the rock type. There was a wide range of measured dust and quartz concentrations within most occupational groups. Much of the variability could be attributed to the month of the survey, implying a possible association with weather and production levels, both of which vary between months. We have also observed clear changes in dust and quartz concentrations directly attributable to changes in work practices and improvements in dust control and differences between the two types of survey could be explained by such improvements. The compliance monitoring results are a useful source of information on dust and quartz exposure, but care will be required to ensure that account is taken of seasonal differences. The results also demonstrate the importance of taking account of changes in work practice and dust control measures when estimating past exposures to any workplace pollutant.