If you have just disturbed asbestos, do this now
- Stop work and stop anyone else entering the area. Switch off any tool or fan that is moving air around.
- Do not sweep, dry-vacuum or wipe it up. That throws fibres into the air. Leave the debris where it is.
- Get clear, and keep anyone with visible dust on them in one place. Do not walk it through the rest of the site, your van or your home.
- Tell your supervisor or the general contractor straight away, and put it in writing.
- Treat anything you suspect as asbestos until a sample is tested - older drywall and joint compound, vinyl floor tile, pipe and duct insulation, ceiling texture, roofing and siding are common sources in pre-1990 buildings.
- It is not a DIY clean-up. Suspect material must be assessed and removed by a qualified asbestos abatement contractor under your province's asbestos regulations, and worker exposure reported to your provincial workers' compensation board (WCB, WSIB or WorkSafeBC).
This is the emergency summary. The rest of this guide explains the exposure limits and the control programs that stop this happening in the first place.
The dust that kills you on a construction site rarely does it that day. Silica and asbestos are the two big long-term hazards in the trades: both are confirmed human carcinogens, both cause disease that shows up ten, twenty or thirty years after the exposure, and both are regulated with hard exposure limits and mandatory control programs. A fall happens in front of you; silicosis and mesothelioma do their damage out of sight. That delay is exactly why these hazards get under-managed, and exactly why the law sets firm limits.
Respirable crystalline silica
Cutting, grinding, drilling or breaking concrete, brick, stone, tile, mortar and engineered stone releases respirable crystalline silica, a Group 1 carcinogen that causes silicosis (irreversible lung scarring) and lung cancer. The occupational exposure limits (OELs) are set per jurisdiction, measured as an 8-hour time-weighted average.
In Ontario the limits for construction are 0.10 mg/m3 for quartz and tripoli, and 0.05 mg/m3 for cristobalite. An important technical point that trips people up: Ontario's designated-substance regulation, O. Reg. 490/09, does not apply to construction projects. On a construction project the duty to control silica falls under O. Reg. 833 (Control of Exposure to Biological or Chemical Agents). Either way, the employer on an Ontario construction site must assess silica exposure, use wet methods or local exhaust ventilation, monitor airborne concentrations, keep worker records, and train workers.
Other jurisdictions set their own numbers. Saskatchewan uses 0.05 mg/m3 for all crystalline silica with periodic monitoring by a qualified person; several provinces follow the lower ACGIH guideline of 0.025 mg/m3, while others sit at 0.1 mg/m3. Always check your own province's current OEL rather than assuming Ontario's figure travels.
The practical controls are the same everywhere and they work: cut wet, use tools with on-tool dust extraction (a shroud and a HEPA vacuum), keep people out of the dust cloud, and fit properly fit-tested respirators where dust cannot be fully controlled. A paper nuisance mask is not protection against silica.
Asbestos
Asbestos was used for decades in pipe lagging, vinyl floor tiles and mastic, textured ceilings, cement board, drywall joint compound, roofing and insulation. Disturbing material that contains it releases fibres that cause asbestosis, lung cancer and mesothelioma, a cancer almost exclusively caused by asbestos. The national OEL for all forms of asbestos is 0.1 fibres per cubic centimetre (f/cc) as an 8-hour time-weighted average.
The legal trap in renovation and demolition is this: in any building constructed or last renovated before the mid-1990s, you must assume asbestos is present and have it surveyed before you disturb anything. Work is then classified by risk, and the terminology varies by province. Ontario (O. Reg. 278/05) uses three types: Type 1 (low risk, such as removing a small area of non-friable material), Type 2 (moderate), and Type 3 (high risk, such as friable material or demolition), where ministry-approved abatement-worker certification is required. British Columbia went further: since 1 January 2024 every asbestos abatement contractor must hold a WorkSafeBC licence, and workers must be certified at one of three levels, the first jurisdiction in Canada to mandate it. Alberta classifies work as low, moderate or high risk with certification required for high-risk work. Quebec, Saskatchewan, Manitoba and the Atlantic provinces run similar type or class frameworks with written abatement plans and air monitoring for higher-risk work.
If you find suspect material mid-job, stop, do not disturb it further, and get it sampled. Never grind, sand or dry-sweep something that might contain asbestos.
WHMIS 2015 and your dust controls
The Workplace Hazardous Materials Information System (WHMIS) 2015 is Canada's hazard-communication standard, aligned with the UN GHS. It runs on a two-part structure: Health Canada governs suppliers (labels and Safety Data Sheets on products sold), and your provincial OHS authority governs your duties as an employer. Your four core obligations are to keep a current inventory of hazardous products, hold a current 16-section Safety Data Sheet (no more than 3 years old) for each, label every container including anything you decant, and provide documented, site-specific training on the actual products your crew handles. Generic online courses alone do not meet the legal standard, and training must be reviewed at least annually.
The real long-term risk
This is the part that matters most and gets ignored most. Silicosis, asbestosis, lung cancer and mesothelioma have latency periods measured in decades. A tradesperson who cuts concrete dry through their twenties and thirties may feel fine until their fifties or sixties, when the disease finally surfaces and is incurable. The controls are cheap and effective compared with the outcome: water, on-tool extraction, a fit-tested respirator and not standing in the cloud. Build the habit young, because there is no treatment that gives the lungs back later.
Common mistakes
- Citing the wrong Ontario silica regulation. On a construction project the duty is under O. Reg. 833, not the designated-substance O. Reg. 490/09.
- Cutting masonry dry. A dry cut-off saw in still air is one of the highest silica exposures on site; wet-cut or use on-tool extraction.
- Skipping the pre-renovation asbestos survey. In a pre-1990s building you must assume asbestos and survey before disturbing material.
- Relying on a nuisance dust mask. Silica and asbestos protection needs a properly fit-tested respirator, not a loose paper mask.
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