The Silica Control Tool is a web-based tool developed by the British Columbia Construction Safety Alliance (BCCSA) to help construction employers manage occupational exposure to respirable crystalline silica (RCS). The BCCSA is a not-for-profit association with a mandate to provide health and safety resources and services to the local construction industry. Construction companies are primarily small businesses, and many do not have access to occupational hygiene data or expertise. The Silica Control Tool uses a database of RCS exposure measurements from construction work sites to help employers generate RCS exposure estimates for their work activities and environments. The tool aims to connect employers with exposure data and help them use that data to create an effective exposure control plan (ECP). RCS BACKGROUND AND REGULATIONS Crystalline silica, or silicon dioxide, is a naturally occurring mineral that is ubiquitous in the earth’s crust and has been a known occupational health hazard for centuries. Crystalline silica is commonly found at construction work sites in rocks, sand, and earth and is also present in construction materials, including concrete, cement, brick, mortar, asphalt, and gypsum. Construction work activities that disturb and fracture these materials generate dust containing respirable crystalline silica, which may be inhaled by workers. Inhalation of RCS can cause serious health impacts primarily on the respiratory system, such as silicosis, an irreversible and sometimes fatal form of pulmonary fibrosis. RCS has been classified by the International Agency for Research on Cancer as a Group 1 carcinogenic agent, meaning there is strong evidence that it causes cancer in humans. Exposure to RCS has also been linked to an increased risk of chronic obstructive pulmonary disease, tuberculosis, and kidney disease. ACGIH has set a time-weighted average (TWA) threshold limit value (TLV) of 0.025 mg/m3 of RCS. This TLV reflects the potential for RCS to cause serious impacts even at low levels of exposure. In 2016, OSHA announced updated silica exposure regulations that reduced the agency’s TWA permissible exposure limit (PEL) for RCS from 0.1 mg/m3 to 0.05 mg/m3. The rule also requires employers to use engineering and administrative controls to control exposure to RCS and to use respiratory protection when other controls cannot reduce exposure levels below the PEL. A construction standard for RCS was published as part of the final rule, and enforcement began in 2017. In Canada, occupational health and safety is regulated by provincial governments. The regulatory authority in British Columbia, WorkSafeBC, has adopted the ACGIH TLV of 0.025 mg/m3 as the occupational exposure limit. Under a substance-specific requirement for RCS added to the regulation in 2017, employers must create a written exposure control plan (ECP) for any workplace where workers are or may be exposed to RCS at levels that exceed 0.025 mg/m3. The ECP must specify the exposure controls used to control RCS levels and employers must use air monitoring data to demonstrate that their selected controls can reduce exposure levels below 0.025 mg/m3. CHALLENGES FOR RCS MONITORING Monitoring silica levels in workers’ breathing zones is necessary for selecting controls and verifying their effectiveness. But conducting air monitoring in the construction industry is challenging due to the variable nature of construction work. On-site hazards and conditions change from day to day, and construction projects often employ multiple trades who come and go at short notice. There are no direct-reading RCS measurement methods. In the days required to obtain analytical results from RCS monitoring, a project may move on to other tasks and exposure scenarios. Moreover, in BC, as in many other jurisdictions, more than 90 percent of construction employers have fewer than 20 employees. Employers typically do not have industrial hygienists on staff, and there are insufficient consultants available to frequently monitor RCS exposure levels. Recognizing the challenges that construction employers face to collect air monitoring data, the WorkSafeBC regulation permits employers to use data from “equivalent work operations” to demonstrate compliance. The OSHA standard for RCS in the construction industry (29 Code of Federal Regulations 1926.1153) includes a similar clause allowing the use of “objective data.” However, most construction employers and their staff lack the training or experience to identify or access peer-reviewed studies or published exposure monitoring reports, evaluate the equivalence of work operations, and determine whether data were collected using valid sampling and analysis methods. Alternative methods exist that permit employers to achieve compliance without collecting and evaluating air monitoring data. For example, OSHA’s construction industry standard for RCS specifies combinations of controls employers can use to achieve regulatory compliance for common construction activities. Modeling tools are another option. In 2013, researchers at the Université de Montréal and the Institut de Recherche Robert-Sauvé en Santé et en Sécurité du Travail in Quebec, Canada, published their analysis of a database of RCS exposure measurements from construction work sites. This database was assembled from measurements reported in scientific journals, research reports, and government and institutional databases. The team’s analysis demonstrated that “task-based” samples, as opposed to full-shift sampling, could be used to develop a model that predicted RCS exposure levels. Their statistical model used work task, construction sector, construction project type, work environment (for example, indoor or outdoor workplaces), presence of general ventilation, and use of engineering controls to estimate RCS exposure. The final model explained 60 percent of the variability in RCS exposure data in the database. In Europe, several tools have been developed to assist exposure modeling for regulatory compliance, including the Advanced REACH Tool (ART), the Estimation and Assessment of Substance Exposure (EASE) model version 2.0, Stoffenmanager, and the ECETOC Targeted Risk Assessment (TRA) tool. There are several benefits to using a modeling approach for exposure assessment and risk assessment. First, a model can be calibrated to regulations and requirements used by other jurisdictions. Second, a model can be used to demonstrate the effect of exposure controls on exposure levels. It can also be updated with new measurements to respond to changes in work practices and control technologies. Collecting exposure measurements from employers can encourage industry engagement with exposure monitoring. Finally, exposure measurements collected by industry can be used beyond a one-time compliance assessment to inform the whole industry, rather than an individual employer.

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