SILICA DUST EXPOSURE ON CONSTRUCTION SITES — WHAT ONTARIO WORKERS NEED TO KNOW

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Crystalline silica is one of the most dangerous airborne hazards on Ontario construction sites, and it is everywhere. Concrete, brick, stone, mortar, sand — these materials all contain silica. Every time a worker cuts a concrete slab, grinds a block wall, drills into masonry, or sweeps up dust from a demolition, they are potentially breathing in microscopic particles that can scar their lungs permanently.

The problem is that silica dust is often invisible to the naked eye. The most harmful particles — those under 10 micrometres — are small enough to bypass the body's natural defences and lodge deep in lung tissue. You cannot see them, you cannot taste them, and by the time symptoms appear, the damage is already done.

What Is Crystalline Silica?

Crystalline silica is a naturally occurring mineral found in the earth's crust. The most common form is quartz, which makes up a significant portion of sand, granite, and most concrete and masonry products used in construction. When these materials are cut, ground, drilled, crushed, or otherwise disturbed, they release fine respirable dust containing crystalline silica particles.

Construction activities that generate the highest silica dust exposures include:

• Concrete cutting and sawing — wet or dry cutting of slabs, walls, and curbs with abrasive or diamond blades
• Grinding and polishing concrete — surface preparation, smoothing, and finishing
• Drilling and coring — creating holes in concrete, brick, or stone for anchors, conduit, or plumbing
• Demolition — breaking apart concrete and masonry structures with jackhammers, breakers, or heavy equipment
• Tuck-pointing and mortar removal — grinding out mortar joints in brickwork, one of the highest-exposure tasks in construction
• Abrasive blasting — using sand or other silica-containing media to clean or prepare surfaces
• Sweeping and cleanup — dry sweeping of dust from cutting and grinding operations

Ontario's Occupational Exposure Limit

Ontario's occupational exposure limit (OEL) for respirable crystalline silica is 0.025 mg/m³ as an 8-hour time-weighted average. This is set out in Ontario Regulation 833 — Control of Exposure to Biological or Chemical Agents, under the Occupational Health and Safety Act.

To put that number in context, 0.025 milligrams per cubic metre of air is an extraordinarily small amount. A single grain of sand weighs roughly 50 milligrams — about 2,000 times more than the maximum permissible airborne concentration over an entire shift. This gives you a sense of just how dangerous even trace amounts of respirable silica can be.

When air monitoring shows that workers are exposed at or above 50 percent of the OEL, the employer must take action to reduce exposure and implement a control program.

Engineering Controls — Stopping Dust at the Source

Ontario's regulations follow the hierarchy of controls. Engineering controls that eliminate or reduce dust at the source are the first line of defence, and they are far more effective than relying on respirators alone.

• Wet cutting and wet drilling — water suppression is the single most effective method of controlling silica dust. A continuous water feed on a concrete saw can reduce airborne silica by 80 to 95 percent compared to dry cutting. Every concrete saw, masonry saw, and core drill should be equipped with a water attachment.
• Local exhaust ventilation (LEV) — vacuum extraction systems attached directly to the tool capture dust at the point of generation. HEPA-filtered vacuum systems paired with grinders, drills, and tuck-pointing tools can reduce exposure dramatically. The key is ensuring the shroud fits the tool properly and the vacuum has sufficient airflow.
• Enclosures and isolation — containing the dust-generating process within a physical barrier keeps contaminated air away from workers. This can include temporary enclosures for indoor grinding operations or blast cabinets for abrasive blasting.
• Ventilation — in enclosed or semi-enclosed spaces, general dilution ventilation can help reduce ambient dust levels, but it should be used as a supplement to source controls, not a replacement.

Dry cutting concrete without any dust controls is one of the fastest ways to exceed Ontario's silica OEL. A worker operating a dry concrete saw in an enclosed area can be exposed to silica levels 50 to 100 times the legal limit within minutes.

Respiratory Protection

When engineering controls cannot reduce exposure below the OEL, or while controls are being implemented, respiratory protection is required. In Ontario, the selection and use of respirators must follow CSA Standard Z94.4.

• N95 filtering facepiece respirators — suitable for lower-level exposures (up to 10 times the OEL) and short-duration tasks. Must be fit-tested to the individual worker.
• Half-face elastomeric respirators with P100 filters — provide better protection (up to 10 times OEL), a more reliable seal, and reusable cartridges. A solid choice for regular concrete work.
• Full-face respirators with P100 filters — protect the eyes as well as the lungs and offer a higher assigned protection factor (up to 50 times OEL).
• Powered air-purifying respirators (PAPRs) — use a battery-powered blower to push filtered air into a hood or facepiece. More comfortable for extended use in hot conditions.

Fit testing is mandatory. A respirator that does not seal properly provides little to no protection. Workers must be clean-shaven where the respirator contacts the face — beards, stubble, and sideburns will break the seal.

Medical Surveillance

Workers regularly exposed to silica dust should be enrolled in a medical surveillance program. This typically includes:

• Baseline chest X-ray and lung function test — conducted before or shortly after the worker begins silica-exposed work
• Periodic follow-up — chest X-rays and spirometry every 1 to 3 years, depending on exposure levels and duration
• Health questionnaire — screening for symptoms such as persistent cough, shortness of breath, or chest tightness

Medical surveillance allows early detection of silicosis and other lung diseases before they progress to the point where they are debilitating or fatal.

What Is Silicosis?

Silicosis is an incurable, progressive lung disease caused by inhaling respirable crystalline silica. The silica particles trigger inflammation and scarring (fibrosis) in the lungs, reducing their ability to absorb oxygen. There are three forms:

• Chronic silicosis — develops after 10 or more years of lower-level exposure. This is the most common form and may go undetected for years.
• Accelerated silicosis — develops within 5 to 10 years of higher-level exposure. Progresses faster and more aggressively than the chronic form.
• Acute silicosis — develops within weeks to months of extremely high exposure. This form is rapidly fatal and has been documented in workers performing dry abrasive blasting with silica sand or uncontrolled concrete grinding in enclosed spaces.

Silicosis also dramatically increases the risk of tuberculosis, lung cancer, kidney disease, and autoimmune disorders. There is no cure — once lung tissue is scarred, it does not heal. Treatment focuses on slowing progression and managing symptoms.

Your Responsibilities as a Worker

Under the OHSA, workers have responsibilities too. You are required to use the protective equipment and engineering controls provided by your employer. If you are assigned a respirator, wear it. If a wet cutting attachment is available, use it. If you see a co-worker dry-cutting concrete without any dust controls, say something — because the dust they generate does not stay in their breathing zone alone.

You also have the right to refuse unsafe work under Section 43 of the OHSA. If you are asked to perform silica-generating tasks without adequate controls or protection, and you believe this creates a danger to your health, you have the legal right to refuse and to have the situation investigated.

Silica dust is not a minor nuisance. It is a confirmed carcinogen and a cause of fatal lung disease. Treat it with the same seriousness you would treat any other lethal hazard on a construction site.