Isocyanate exposure control in motor vehicle paint spraying: evidence from biological monitoring

Abstract

The purpose of this work was to assess the changes in control of exposure to hexamethylene diisocyanate based paints used in vehicle spraying after a Health & Safety Executive (HSE) national project. Paint sprayers and managers from motor vehicle repair (MVR) bodyshops across the UK, were invited to one of 32 Safety and Health Awareness Days (SHADs) to increase their understanding of the hazards, and practical ways of controlling of exposure to isocyanate based paints. Exposure measurement based on biological monitoring was offered, free of charge, to each of the roughly 4000 participants and used to assess the effectiveness of controls and methods of working. Results are compared with pre and post SHAD measurements. Urine samples were received from 995 paint sprayers. Hexamethylene diamine (HDA) levels in urine, indicative of exposure to hexamethylene diisocyanate (HDI), were significantly lower (Mann-Whitney, p<0.0001) than had been seen in a wider population from previous HSE inspections and routine sampling. Where a sprayer's urinary HDA was above the quantification limit they were asked to send another sample after reviewing and improving exposure control measures. The results from these repeat samples were significantly lower than the original results. There was no difference in the exposures of sprayers using air-fed half-mask face-pieces compared with visor type air-fed breathing apparatus, or between spray booths and rooms. The analysis of HDA in urine is a useful technique for assessing exposure to isocyanates in paint sprayers. The simplicity of this approach has allowed wide-scale use of biological monitoring in an industry dominated by small and micro businesses. Biological monitoring of exposure has enabled individual companies, and sprayers, to check that their control measures are working. This study showed overall lower levels of HDA in paint sprayers following SHADs. These lower levels have been maintained across a wider population of UK paint sprayers over the succeeding years. Whilst there may be many reasons for the reduction in exposure, the weight of evidence suggests that the key messages about exposure control measures, delivered through the SHADs and other means, were influential.