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
  • mineral deposits

Workers may be exposed to elevated levels of radon gas in indoor and underground environments. Radon does not pose a health risk in outdoor environments because the amount of radon gas is very low because of dilution in the air.

Radon gas is:

  • odourless
  • tasteless
  • colourless (invisible)

It emits ionizing radiation in the form of alpha particles. Alpha particles are a hazard when taken internally, either:

  • by inhaling radon gas
  • by inhaling dust with alpha particles attached
  • by ingesting dust with alpha particles attached

Health effects

The health hazard associated with the inhalation of radon gas is an increased chance of developing lung cancer.

Hazard location

Radon can accumulate to high concentrations indoors in confined or poorly ventilated spaces, and confined subterranean spaces. Radon levels are generally highest in basements, crawl spaces and other underground environments because radon is heavier than air. In addition, these areas are often nearest to the radon source and are some of these areas may not be adequately ventilated.

Industries and workplaces that are prone to radon production and therefore to worker exposure include:

  • underground mines
  • tunneling and underground workings
  • petroleum production
  • water treatment
  • fertilizer manufacturing
  • fish hatcheries
  • metal recycling facilities

Hazard classification

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.

In the table below, the first column includes the average annual concentration of radon, expressed as Bq/m3. Bq stands for Becquerel, which is the derived Système International (SI) unit of radioactivity, defined as a disintegration or emission per second.

Bq/m3 stands for one disintegration (or emission) per second, per cubic metre of air. The second column is the Canadian Guidelines for the Management of Naturally Occurring Radioactive Materials (NORM),  published by Health Canada.

Program classifications for radon and NORM

Average annual concentration of radon [Bq/m3]NORM program classification
800 – 3,000Radiation protection management
200 – 800NORM management
Background – less than 200Unrestricted


The precautions you should take for each classification are outlined below.

Radiation protection management for radon

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 following:

  • their status as a radiation worker
  • risks associated with radiation exposure
  • applicable limits
  • his or her personal measured dose levels

The exposure reduction program should include the following:

  • steps to reduce the radon concentration levels to below 200 Bq/m3 through engineering controls where possible
  • administrative controls
  • personal protective equipment
  • periodic worksite assessments to measure changes in radon levels

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.

NORM management for radon

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.

Take the following steps to reduce exposure:

  • introduction of access controls to prevent public and incidentally exposed worker (whose regular duties do not include exposure to NORM) access to areas with these radon levels
  • changes in work practices
  • reduction of radon concentration levels to below 200 Bq/m3 where possible

The work area radon levels should be assessed periodically to verify conditions have not changed.


The NORM classification is “unrestricted” if the average annual concentration of radon in the air is 200 Bq/m3 or less. Based on Health Canada radon guidelines, these are acceptable levels of radon in buildings, including homes or public buildings, such as:

  • schools
  • hospitals
  • long-term care facilities
  • correctional facilities

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:

  • advised of the presence of radon and
  • given information on the health effects of radon exposure

Key legal requirements

The Canadian Guidelines for the Management of Naturally Occurring Radioactive Materials (NORM Guideline) is 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, Training and Skills Development’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 progeny in underground mines in sections 289 to 293.

When radon decays the following are produced:

  • radon progeny
  • polonium-218
  • lead-214
  • bismuth-214
  • polonium-214

The radon progeny have short half-lives and emit radiation more quickly than radon itself. Polonium-218 and polonium-214 pose a health risk to workers.

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 progeny concentration levels within specific geographic locations in section


Resources on corrective measures, radon remediation and worker training are listed below. We have included links to other websites, but this does not mean that we endorse their information as compliant with the OHSA or the regulations.

Health Canada

Canadian Nuclear Safety Commission (CNSC)

World Health Organization (WHO)

This resource does not replace the Occupational Health and Safety Act (OHSA) and its regulations and should not be used as or considered legal advice. Health and safety inspectors apply and enforce these laws based on the facts they find in the workplace.