Respirable Crystalline Silica Exposures among Stoneworkers involved in Stone Restoration Work

Abstract

Exposure to respirable crystalline silica (RCS) can result in the development of a range of adverse health effects including silicosis and lung cancer. Although exposure to RCS has been characterised in many occupational groups, limited data is available on RCS exposures and suitable exposure controls in restoration stone work. Occupational exposure to RCS in this sector is of particular concern due to the high silica content of the materials used, the challenges in implementing exposure control strategies and the large number of workers potentially affected globally. The objectives of this study were to identify the main determinants of RCS exposure of a group of restoration stoneworkers and to design and execute a workplace intervention to reduce worker exposure to RCS during high exposure tasks. During the exposure assessment, field trials were performed to evaluate the performance of high-flow rate samplers for the collection and assessment of RCS in low silica content materials during restoration stone work. An exposure assessment (n=103) study was designed to characterise RCS exposures amongst a group of stoneworkers involved in the restoration and maintenance of heritage buildings in Ireland. Exposure data was analysed using mixed effects modelling to investigate determinants of RCS exposure and their contribution to the individual¿s mean exposure. Between-depot, between-worker and within-worker variance components were also investigated. High risk RCS exposure tasks, involving angle grinders and sandstone were identified and a technical intervention study was designed to evaluate the effectiveness of commercially available shroud systems at reducing RCS levels. The workplace intervention also included a worker element, involving a questionnaire survey designed to collect information on exposure control usage and worker and organisational factors, influencing worker use of exposure controls. Post implementation of the workplace intervention, the questionnaire survey was re-administered and an exposure assessment was conducted. To investigate the implication of this study for the wider stoneworker community in Ireland, a questionnaire was administered to a convenience sample of stoneworkers. While conducting the exposure assessment at field sites, a short study to evaluate the performance of three high flow rate samplers for the collection of low concentrations of RCS in restoration stonework sites was also performed. The geometric mean (GM) RCS exposure concentrations for all worker tasks ranged from < 0.02 - 0.70 mg/m3 with concentrations for work involving limestone/lime mortar and sandstone < 0.02 - 0.01 mg/m3 and < 0.02 - 0.70 mg/m3 respectively. 67% of the 8-hr time weighted average (TWA) exposure measurements for sandstone exceeded the occupational exposure limit proposed for RCS, 0.05 mg/m3. The 95 percentile for the tasks of cutting and grinding sandstone was greater than the OELV, demonstrating a high probability of non-compliance with the OELV when workers carried out these tasks. Statistical analysis of the data using mixed effects regression found task to be the only significant (P < 0.001) determinant of RCS exposure, with the tasks of grinding and cutting sandstone producing RCS exposures on average 32 and 70 times higher than the task of stone decorating. The variance components for between-depot, between¿worker and within-worker were reduced by 46%, 89% and 49% respectively, after including task in the mixed effects model. The within worker variance component was larger than the between-depot and between worker variance components in the final model. Thus, the workplace intervention focused specifically on the worker task of grinding sandstone and took into account the within worker variability within this group. The Dustie® shroud was selected as the most suitable on-tool shroud, based on worker feedback, and respirable dust concentrations and RCS were both significantly reduced (P < 0.001) when the shroud was in place compared with concentrations without using the shroud. Regression analysis showed that there was a significant (P < 0.001) difference in the levels of respirable dust measured depending on grinding wheel used. A worker training programme was developed including hazard communication, information on exposure controls and the technical intervention. Post intervention task exposure data for grinding sandstone was lower (GM 0.5 mg/m3) than exposure values measured prior to implementation of the Dustie® shroud (GM 0.7 mg/m3). Post intervention workers exhibited a significant improvement in their knowledge of exposure controls and occupational health issues but use of the shroud and some individual barriers to using RPE did not show significant improvement. The fact that the sites were still in the commissioning phase of the intervention is a probable explanation for the low reporting of shroud use post intervention and suggests that the short time period of three months may not be sufficient time to observe a change within this organisation. Results from the survey of Irish stoneworkers showed that this population regularly worked with high silica content materials and nearly 90% used power tools with these materials. Findings also indicated poor health and safety practice and a lack of awareness of the health risks associated with stone work amongst this group. Results from the evaluations of the high flow samplers indicated that most of the quartz mass collected with the high-flow-rate samplers were above the limit of detection, relative to the corresponding low-flow-rate samplers used in the study. This indicated that these samplers were suitable for quantifying exposures from low silica content materials. Feedback received from the workers on the practicality of the high-flow pumps indicated that they were not comfortable to wear and could interfere with their work. This study provides a comprehensive evaluation of exposure to RCS in restoration stone work, and contributes to existing knowledge on exposure controls suitable for this work, enabling professionals in identifying effective controls to reduce RCS exposures in their workplace. Results indicate that there is significant potential for over exposure to RCS amongst restoration stoneworkers and other stoneworkers who work with high silica content materials worldwide, putting them at risk of developing illnesses associated with RCS exposure. There is a need for regulatory bodies to produce more specialised health and safety guidance material for this sector, concentrations of RCS can be significantly reduced by using commercially available on-tool shrouds while grinding sandstone in restoration stone work, however, there is scope for commercially available on-tool shrouds to be further refined. Findings also indicated that worker behaviour had a role to play in the use of the shrouds post intervention and that a technical intervention alongside a behavioural intervention should be implemented with the aim of improving workplace intervention design.