Report from the CCOHS – October 29, 2025
We often think of workplace hazards as things we can hear, smell, touch, or see, such as noise, chemicals, or moving equipment. But there’s a serious health hazard in Canadian workplaces that’s both invisible and has no smell. Radon exposure remains under-recognized in many workplaces, despite its established link to lung cancer.
What is Radon?
Radon is a radioactive gas that forms when uranium in soil and rock breaks down over time. It dissipates quickly outdoors, but indoors, it can build up, especially in basements and ground-floor areas that are poorly ventilated or tightly sealed.
The most significant source of radon is the soil underneath a building, though it can also be present in groundwater or building materials. It can enter through cracks in floors and walls, sump pumps, floor drains, and gaps around pipes. Because radon is a gas, changes in air pressure can also affect its emission from the ground and accumulation in building air.
Once inside, radon breaks down into radioactive particles known as progeny, which attach to dust in the air. When inhaled, these particles can embed in the lungs and emit radiation that damages lung tissue, significantly increasing the risk of cancer.
The International Agency for Research on Cancer (IARC) classifies radon as a Group 1 carcinogen, meaning it is known to cause cancer in humans. Inhaling radon progeny increases the risk of developing lung cancer. According to research by scientists at CAREX Canada, radon exposure is the second leading cause of lung cancer in Canada after smoking. Combine the two, and the risk is significantly increased.
Not just a residential hazard
Though radon has traditionally been seen as a household issue, CAREX Canada estimates that approximately 190,000 people in Canada are exposed to radon at work. Workers in underground mines, particularly uranium mines, face the highest level of exposure. Those involved in tunnelling and underground workings, such as utility tunnel and subway workers, are also at an elevated risk. Though their level of exposure is lower, the occupations with the highest number of workers exposed to radon are administrative assistants, general office support workers, receptionists and elementary school and kindergarten teachers.
Many occupational exposures occur in indoor environments where radon enters from the ground and builds up over time. Some regions, particularly those with uranium-rich rock or soil, are at a higher geographic risk, but elevated radon levels have been found across the country, even in places not traditionally viewed as high-risk. Because radon can be present anywhere in Canada, regardless of region, any workplace with contact to the ground could potentially have unsafe radon levels.
How to keep workers safe
Employers can take several key steps to protect workers from radon. Start by assessing the risk to your workplace based on building type, location, and use of the space. Even if your organization isn’t in a traditionally high-risk sector, your buildings may still present a risk of radon exposure.
The only way to know if radon is present is to test for it. Testing should be initiated for any building where people spend prolonged periods of time, especially those working on lower floors or in older, sealed structures. Testing should follow Health Canada’s recommendations for long-term sampling. Where levels are high, you may need to hire a certified professional to identify appropriate control measures for the workplace.
Make radon awareness a visible part of a proactive safety culture in your workplace by integrating it into regular health and safety education and training, testing regularly, and being transparent with results. With any air sampling, you are required to share test results with workers, who have the right to know about hazards in the workplace.
What testing looks like
It is recommended to test radon exposure for at least three months, ideally during winter when buildings are sealed and radon levels are at their highest. This seasonal timing ensures a more accurate measurement, as less outdoor air is circulating through indoor spaces.
The most common testing method involves using small, disk-shaped devices called alpha track detectors, which are placed in rooms where people spend the most time, particularly in lower-level areas like basements. After three months, these detectors are sent to a lab for analysis. Results are reported in becquerels per cubic metre (Bq/m³). Health Canada’s guideline limit is 200 Bq/m³, a threshold that applies not only to homes but to public buildings such as schools, hospitals, long-term care centres, and correctional facilities.
In underground industries, exposure is often measured using “working level months” (WLM), a unit that reflects long-term exposure to radioactive decay products over time.
What to do when radon levels are high
If test results show radon levels above 200 Bq/m³, mitigation is strongly recommended. Reducing radon may fall under your legal duty to protect workers from known carcinogens. Consult your local occupational health and safety jurisdiction to confirm what the requirements are for your industry.
The most effective approach to mitigation is a method known as sub-slab depressurization, in which a pipe and fan system is installed to draw radon from beneath the building and vent it outside before it can enter the indoor air. Other actions can include sealing foundation cracks or gaps and improving overall ventilation. The effectiveness of each method depends on how high the radon levels are and the building’s construction features. In many cases, these systems are affordable and unobtrusive, offering peace of mind without major renovation. Refer to the Canadian National Radon Proficiency Program (C-NRPP) for a list of certified professionals qualified to assess and mitigate radon.
After mitigation, Health Canada recommends retesting to confirm that radon levels have been reduced and the corrective measures are effective.
Separating fact from fiction
A few common misconceptions about radon are that exposure is only an issue in older or rural buildings, that radon testing is expensive, and that radon is only a concern in residences. In truth, radon can affect any structure in contact with the ground, regardless of its age or location. Radon is impossible to detect without testing, and radon test kits are easy to use and affordable, both in the workplace and at home. Readily available research shows that radon exposure affects indoor and underground workers across several sectors, not just residents and workers in homes.
Understanding radon legislation
In Canada, legislation addressing radon varies by jurisdiction. Industries such as mining or uranium handling typically have specific exposure limits and requirements. These workers are often monitored through the National Dose Registry, managed by Health Canada.
The Canadian Nuclear Safety Commission has published dose limits for radiation exposure, and several provincial occupational health and safety authorities have adopted values that apply either broadly or to specific sectors. Consult your local occupational health and safety jurisdiction for more information.
The most effective way to address the silent threat of radon is to take proactive steps. Educate workers about the risks, make sure to test for radon regularly, share the test results, and encourage everyone to test their homes as well. Protecting workers from radon exposure is not only a matter of compliance; it’s also an investment in their long-term health, safety, and peace of mind.
My opinion
I wondered about my father having a terminal cancer and him working in and out of basements for most of his working life.
Something to think about. Key Radon Limits and Guidelines:
- Residential Guideline (Canada):200 Bq/m³ (Action recommended).
- Residential Guideline (WHO):100–300 Bq/m³.
- Occupational Exposure (Progeny):3 Working Levels (WL) or roughly
WLM per year.
- Occupational Exposure (Mining/Other):1-2 WLM per year are often recommended as safe practice.
I would suggest that a professional come in and test your basement for radon.
HRS Group Inc. has a great team that can help you with all your health and safety needs. Contact Deborah toll free at 1-877-907-7744 or locally at 705-749-1259.
Ensure your workplace is a safe place.
Remember – In Ontario, “ALL Accidents are Preventable”
‘Work’ and ‘Play’ safe.
Daniel L. Beal
CHSEP – Advanced Level
CEO & Senior Trainer
HRS Group Inc.