Disclaimer: This resource has been prepared to help the workplace parties understand some of their obligations under the Occupational Health and Safety Act (OHSA) and regulations. It is not legal advice. It is not intended to replace the OHSA or the regulations. For further information please see full disclaimer.
Workers may be exposed to elevated levels of radon gas in indoor environments. Due to dilution in outdoor environments, the amount of radon gas is very small and does not pose a health risk.
Radon gas, also known chemically as radon 222, is a naturally occurring radioactive material (NORM) that is produced during a decay process from the radioactive element uranium, which can be found globally in soil, bedrock, and mineral deposits.
Radon gas is odourless, tasteless, and colourless (invisible). It emits ionizing radiation in the form of alpha particles. Alpha particles are a hazard when taken internally, by inhalation of the radon gas, inhalation of dust with alpha particles attached, or ingestion of dust with alpha particles attached.
The health hazard associated with the inhalation of radon gas is an increased chance of developing lung cancer.
Radon can accumulate to high concentrations indoors in confined or poorly ventilated spaces, as well as in confined subterranean spaces. Radon levels are generally highest in basements and crawl spaces because radon is heavier than air. In addition, these areas are often nearest to the radon source and are usually poorly ventilated.
Industries and workplaces that are prone to radon production and therefore to worker exposure include: underground mines and tunneling/underground workings, as well as petroleum production, water treatment, fertilizer manufacturing, fish hatcheries and metal recycling facilities.
Workplaces can be classified based on their average annual concentration of radon. Measurements should be made to estimate the average annual radon gas concentrations in radon-prone workplaces.
|Average annual concentration of radon [Bq/m3] ||NORM program classification |
|800 – 3,000||Radiation Protection Management|
|200 – 800||NORM Management|
|Background – less than 200||Unrestricted|
 Bq stands for Becquerel, which is the derived Système International (SI) unit of radioactivity, defined as a disintegration or emission per second. Bq/m3 therefore stands for one radioactive transformation per second, per cubic metre of air.
 As per the Canadian Guidelines for the Management of Naturally Occurring Radioactive Materials (NORM), published by Health Canada.
The precautions which should be taken for each classification are outlined below.
The NORM classification is “Radiation Protection Management” when the estimated annual average concentration of radon gas is more than 800 Bq/m3 (translating to an annual effective dose of greater than 5 milliSievert (mSv/year). A Sievert is the SI unit of dose equivalent, defined as the absorbed dose multiplied by a quality factor (biological effectiveness of the type of radiation).
A Radiation Protection Management program should be implemented. This should include the initiation of a dose monitoring program to track the annual effective dose to the worker, both estimated and measured.
The employer should inform each occupationally exposed worker of:
The exposure reduction program should include:
An occupationally exposed worker should not be exposed to an annual average concentration of radon gas exceeding 3,000 Bq/m3, which represents an annual effective dose of 20 mSv for occupationally exposed workers.
The NORM classification is “NORM Management” when the estimated annual average concentration of radon gas in an occupied area is more than 200 Bq/m3 but less than 800 Bq/m3. This translates to an annual effective dose of 1 to 5 mSv.
Steps to reduce this exposure should be taken, including:
The work area radon levels should be assessed periodically to verify conditions have not changed.
Based on Health Canada radon guidelines, acceptable levels of radon within buildings, including homes or public buildings such as schools, hospitals, long-term care facilities, correctional facilities, is 200 Bq/m3 in air.
This value is also the derived working limit for radon, as based on the annual limit on intake of radon a worker can ingest or inhale each year, which would result in a committed dose equal to an annual effective dose of 1 mSv. Where the annual average concentration of radon gas is expected to be above 200 Bq/m3, measurements should be made to estimate the average annual radon gas concentration.
To prevent hazardous exposure levels or reduce radon concentration, an employer should seek professional assistance from private sector consultants who specialize in radon testing and radon remediation. Health Canada recognizes the Canadian National Radon Proficiency Program (C-NRPP), which certifies radon testers.
Occupants of buildings with radon concentration levels higher than 200 Bq/m3 should be:
The Canadian Guidelines for the Management of Naturally Occurring Radioactive Materials (NORM Guideline) are considered the industry standard for NORM protection in workplaces.
The general duty clause of Ontario’s Occupational Health and Safety Act (OHSA), clause 25(2)(h), states that an employer must take every precaution reasonable in the circumstances for the protection of a worker. This includes protecting workers from the hazards associated with radon exposure. When enforcing the general duty clause, the Ontario Ministry of Labour’s Radiation Protection Service may take the NORM Guideline and its recommendations into consideration.
Regulation 854 (Mines and Mining Plants), made under the OHSA, addresses workplace responsibilities with respect to radon daughters in underground mines in sections 289 to 293.
In addition, it should be noted that various sector regulations under the OHSA have requirements regarding the establishment of measures and procedures with respect to the hazards of physical agents present in the workplace and regarding the training of workers who may be exposed to physical agents in the workplace that may endanger the worker’s health or safety.
Additionally, Ontario Regulation 332/12 (Building Code), made under the Building Code Act, addresses radon 222 and radon daughter concentration levels within specific geographic locations in section 126.96.36.199.
Resources on corrective measures, radon remediation and worker training are listed below.
Canadian Nuclear Safety Commission (CNSC):
World Health Organization (WHO):
ISBN: 978-1-4606-7599-1 (HTML)
Disclaimer: This web resource has been prepared to assist the workplace parties in understanding some of their obligations under the Occupational Health and Safety Act (OHSA) and the regulations. It is not intended to replace the OHSA or the regulations and reference should always be made to the official version of the legislation.
It is the responsibility of the workplace parties to ensure compliance with the legislation. This web resource does not constitute legal advice. If you require assistance with respect to the interpretation of the legislation and its potential application in specific circumstances, please contact your legal counsel.
While this web resource will also be available to Ministry of Labour inspectors, they will apply and enforce the OHSA and its regulations based on the facts as they may find them in the workplace. This web resource does not affect their enforcement discretion in any way.