Silica Exposure: Workplace Risks, Laws, and Prevention in Ontario
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Silica exposure remains one of the most significant (and often underestimated) occupational health hazards in construction. Found in many common building materials, respirable crystalline silica (RCS) is serious health risks to workers and creates major compliance concerns for employers.
If silica is a concern in your workplace, it’s important to know your legal responsibilities, its health risks, and how to manage silica hazards before they lead to costly orders or illness.
Silica exposure remains one of the most significant (and often underestimated) occupational health hazards in construction. Found in many common building materials, respirable crystalline silica (RCS) is serious health risks to workers and creates major compliance concerns for employers.
If silica is a concern in your workplace, it’s important to know your legal responsibilities, its health risks, and how to manage silica hazards before they lead to costly orders or illness.
Already received a silica-related order or have concerns about workplace compliance? Schedule a free 30-minute consultation with a Registered Occupational Hygienist.
What Is Silica and Why Is It Harmful?
Crystalline silica is a naturally occurring mineral found in sand, stone, concrete, brick, and mortar. It is commonly found on construction sites, in gravel pits and quarries, in manufacturing, and other industries across Ontario. When these materials are cut, drilled, ground, or demolished, they release tiny airborne particles known as respirable crystalline silica (RCS).
These particles are small enough to bypass the body’s natural defenses and reach deep into the lungs. Prolonged or repeated exposure can lead to serious and irreversible health outcomes, including:
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Silicosis – a progressive lung disease caused by scarring of lung tissue
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Lung cancer – silica is classified as a Group 1 carcinogen by the International Agency for Research on Cancer.
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Chronic Obstructive Pulmonary Disease (COPD)
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Kidney disease, rheumatoid arthritis, and autoimmune disorders
Did you know? Around 153,000 Ontarians are exposed to silica at work, including those in construction, mining, manufacturing, and agriculture (Cancer Care Ontario and the Occupational
Cancer Research Centre).
WorkBright helped our health and safety team with an occupational hygiene assessment. Mike communicated effectively and prepared our team for the day. His findings were thorough and clear to understand which gave us and our employees confidence. We truly value his expertise.
Questions about silica in your workplace?
High-Risk Construction Tasks Involving Silica Exposure
Silica is commonly released into the air during tasks that involve:
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Cutting or grinding concrete, brick, tile, or stone
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Abrasive blasting (especially with silica-containing blast media)
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Drilling, chipping, or jackhammering
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Demolition of concrete and masonry
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Tunnelling and earth moving
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Dry sweeping of dust or use of compressed air
Some of these tasks are known to release higher amounts of silica into the air. For example, abrasive blasting is known to generate higher airborne concentrations of silica compared to drilling a 1/8-inch hole in concrete.
Silica Exposure and Legal Requirements for Employers
Under Ontario’s Occupational Health and Safety Act (OHSA) and related regulations, employers have a duty to protect workers from hazardous exposures, including silica.
Regulation 833: Control of Exposure to Biological or Chemical Agents
Employers are required under section 4 of this regulation to limit the exposure of workers to airborne silica in accordance with the following value set out in the “Ontario Table”:
Crystalline silica – quartz
0.10 mg/m3 (respirable*)
See: Regulation 833, Control of Exposure to Biological or Chemical Agents
*means that size fraction of the airborne particulate deposited in the gas-exchange region of the respiratory tract and collected during air sampling with a particle size-selective device that, (a) meets the ACGIH particle size-selective sampling criteria for airborne particulate matter; and (b) has the cut point of 4 µm at 50 per cent collection efficiency.
Regulation 490: Designated Substances
This regulation applies to every employer and worker where silica exposure is likely. Employers must
1. Assess and document silica exposure
2. Control exposure. Based on assessment findings, an employer may need to implement control measures that include:
- Monitoring procedures for silica
- Ventilation or enclosures to prevent silica from becoming airborne
- Job procedures and practices such as warning signs, barriers, or job rotations
- Hand washing or shower facilities
- Maintain personal records
- Training of supervisors and workers on silica.
Ontario Guideline: Silica on Construction Projects Guideline
This Ontario guideline helps employers and workers in the construction industry understand and manage the hazards of silica. It outlines:
1. The classification of silica work into Type 1, 2, or 3 operations
2. Control measures including ventilation, enclosures, and PPE
3. Employer legal duties under the OHSA, including hazard identification, training, and supervision
4. Procedures for controlling airborne silica on job sites, such as using water
5. Medical surveillance and hygiene practices to protect worker health.
Reminder:
O. Reg. 490/09 does not directly apply to all construction projects, but employers are still required to control exposure to silica in the air under the Regulation 833.
Controlling Silica Exposure: What Employers Should Be Doing
Silica-related hazards should be controlled using the hierarchy of controls:
1. Elimination & Substitution
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Eliminating or substituting silica-containing materials where possible can be quite effective. Although this may not be possible in every situation, sometimes workplaces could eliminate the need to cut, drill or polish silica-containing materials on-site. Instead this could be done in a controlled environment such as a shop.
2. Engineering Controls
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Use wet methods for cutting/drilling
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Implement local exhaust ventilation systems
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Fully or partially enclose high-risk work zones
3. Administrative Controls
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Post warning signs and restrict access to dust-generating areas
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Rotate tasks to reduce worker exposure time
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Provide hygiene and cleanup protocols (no dry sweeping!)
4. Personal Protective Equipment (PPE)
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Provide proper respirators with fit testing and maintenance
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Use protective clothing and ensure it’s decontaminated correctly
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Implement a respirator program as per CSA Z94.4.
Is Your Workplace in Compliance?
If you’re unsure whether your worksite meets Ontario’s silica safety requirements, the first step is to conduct a silica exposure assessment. This involves:
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Identifying where silica may be present
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Monitoring airborne concentrations of RCS
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Classifying the work under Type 1, 2, or 3
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Implementing appropriate control measures and documentation
A professional occupational hygiene assessment can help you not only identify risk, but also avoid health and safety contraventions, protect workers, and meet due diligence obligations.
WorkBright Can Help
At WorkBright, we work with employers across Ontario to:
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Conduct air monitoring for respirable crystalline silica
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Develop compliant exposure control plans
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Advise on engineering controls, PPE selection, and hygiene practices
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Provide documentation and guidance during MOL investigations or WSIB claims
Speak with a Registered Occupational Hygienist
Explore our full Occupational Hygiene Assessment Services to learn how we help keep your workplace safe and compliant.