Modélisation de l’exposition à la silice cristalline dans le secteur de la construction

Chronic inhalation of respirable inorganic dusts containing crystalline silica is linked to occupational respiratory diseases such as lung cancer and silicosis.  Several studies have documented the overexposure to respirable crystalline silica in construction workers, as this compound is found in several building materials and many operations can release fine suspended particles.  Comprehensive quantitative exposure assessment in this industry is challenging due to the variety in tasks performed, materials used and environmental conditions between work sites, the mobile workforce and the temporary nature of construction sites.  An occupational exposure database of silica exposure was compiled from the literature by a research group from the Université de Montréal and the Institut de recherche en santé et en sécurité du travail (IRSST) to address this issue. The exposure data contained in the database were separated on the basis of sampling strategies, which resulted in two separate – but complementary – analyses.  The first analysis was restricted to samples collected to compare levels with an occupational exposure limit, in order to estimate work-shift respirable crystalline silica exposure by construction trade.  The second analysis used measurements collected under a task-based sampling strategy in order to estimate the exposure levels associated with specific activities.  Monte-Carlo simulation was used to recreate individual exposures from measurements reported as summary statistics. Modeling was performed using Tobit models within a multimodel inference framework, with construction trade, task, sampling duration, year and strategy, project type, construction sector, workspace and control methods as potential predictors. The dataset for the analysis by construction trade was comprised of 1346 exposure measurements and included 11 trade categories.  The model containing all the variables explained 22% of the exposure variability and the sampling duration, year and strategy were identified as important predictors.  Civil engineering and roadwork sites as well as new construction projects were associated with lower exposure levels, while the use of control methods reduced silica concentrations by 18% outdoors and 24% indoors.  Predicted geometric means (GM) for year 1999 were the highest for drillers (0.214 mg/m3), underground workers (0.191 mg/m3), roofers (0.146 mg/m3) and cement grinders/finishers (0.125 mg/m3), based on a 8-hour shift.  Heavy equipment operators (0.041 mg/m3) and foremen (0.047 mg/m3) had the lowest predicted GMs. 1566 task-based measurements, representing 27 task categories, were included in the activity-specific dataset.  The proportion of variance explained by the model containing all the variables was 59%, and all the variables investigated had a strong influence on the exposure levels.  Predictions were made based on the year 1998 and the median duration by task in the dataset.  The largest predicted GMs were associated with the following operations: scabbling concrete (1.446 mg/m3), chipping with other tools (0.354 mg/m3), abrasive blasting (0.349 mg/m3) and tuck point grinding (0.200 mg/m3).  Important reductions in exposure levels were found with the use of tool-integrated water sprays (-80%) and local exhaust ventilation (-64%). Important overexposure to the ACGIH Threshold Limit Value and the Québec exposure limit was found for all the trades investigated, indicating a long-term risk of silica-related occupational diseases.  The results of the task-based analysis suggest that this sampling strategy provides a better characterization of the factors affecting exposure and the impacts of engineering dust control methods to control long-term exposure levels.

Keyphrases: construction, crystalline silica, occupational exposure database, exposure assessment