Summary

Silica is one of the most prevalent inorganic compounds found in nature. As crystalline quartz, it is abundant in various minerals, including granite and sand. When materials containing crystalline silica are handled, quartz can be found as suspended dust in the air. If this dust is inhaled by workers, it can cause various respiratory tract diseases, the most serious being silicosis and lung cancer.
In the construction industry, occupational exposure to crystalline silica is common in several trades due not only to its presence in many handled materials, for example concrete, mortar and brick, but also to the processes, involving operations such as breaking, grinding or sawing. In Québec, as in other jurisdictions, the crystalline silica exposure levels in the construction industry still frequently exceed the regulatory limit values. A number of occupational diseases are compensated in this industry in Québec by the Commission de la santé et de la sécurité du travail.
The construction field is complex, with many trades, tasks, materials and tools that can be linked to crystalline silica exposure. Québec occupational health and safety practitioners do not have at their disposal a knowledge review that would allow preventive actions to be ranked in relation to the Québec reality in this activity sector. The production of such a portrait was the general objective of this study, with the more specific objectives being to identify the most hazardous occupations and tasks in relation to their exposure level, and to identify the various means of controlling exposure, while documenting their effectiveness and developing a relational database on silica dust exposure that compiles the literature data in a format that can be used by researchers or practitioners.
One key aspect of the method consisted of developing a database on work-related silica exposure in construction, from an exhaustive search of the international scientific literature (articles from periodicals, reports of public and private organizations, and databases). This database would associate measurement results (exposure levels) with a series of qualifying parameters, linked to the exposure and sampling conditions. This strategy was preferred to the more classic literature review method, which consists of individually analyzing the data from journal articles and synthesizing the information in tables that present each study separately, but which make the diverse data difficult to interpret. In total, of more than 500 documents, 116 were retained because they contained relevant information on exposure levels. Furthermore, 67 documents that dealt specifically with control methods were analyzed.
The exposure database associates 4251 respirable crystalline silica exposure levels with 76 parameters, mainly the occupation, task, tool, material and control methods used. The descriptive analysis of the data indicates that the most hazardous occupations in construction can be classified in three groups based on their exposure level. Underground workers (specialized labourers, pipeline labourers, surveyors and drillers) and heavy equipment operators at the controls of tunneling machines make up an initial group, exposed to levels clearly above (two to four times) the Québec regulatory value. Cement finishers, bricklayer-masons, drillers, specialized labourers and heavy equipment operators at the controls of road-milling machines represent a second group, exposed on average to levels above or close to the regulatory value. Specialized labourers (tile setters), unskilled labourers, fixed and mobile machine-tool operators, and heavy equipment operators (other than road-milling machine and tunneling machine operators) represent a third group exposed to levels between 50–100% of the regulatory value.
The tasks and tools with the highest exposure (all more than twice the regulatory value during the duration of the task) are, in decreasing order: sawing masonry with a portable masonry saw, bush hammering, breaking pieces of masonry (chipping jackhammers on concrete or ceramic), tunnel boring (tunneling machine), and brick/stone joint grinding (tuck point grinding).
The literature review indicates that crystalline silica substitution must be encouraged when possible, but most of the time is difficult to consider in the construction industry due to its presence in numerous basic materials used. The technical means for controlling exposure, such as spraying and local exhaust ventilation, integrated into the tools, are well known and significantly reduce the concentration of crystalline silica dust in the air, with an efficiency generally exceeding 90%. However, these means do not ensure compliance, in the great majority of cases, with the exposure limit values of the different countries and organizations, and have a negative impact on performance. It is therefore recommended that the use of these technical methods be improved as much as possible, and that good practices be applied, for example by adopting certain work methods that produce less dust and by adjusting and maintaining the tools and equipment. It is recommended that respiratory protection be used in conjunction with these methods.
The present study should ultimately involve the development of plain language documents for this industry’s workers and employers that focus on the available control methods in relation to the various tasks performed and tools used. Furthermore, the occupational exposure database developed in this project should be modeled, in order to study in detail the impact of the many parameters controlling occupational crystalline silica exposure in construction. As well, the time period covered by the literature review should be extended to years prior to 1990 to make the database applicable to the retrospective evaluation of silica exposure.