Radon is radiation. It is a naturally occurring colourless and odourless radioactive gas that stems from the nuclear decay of uranium which makes up a large portion of the Earth's crust.

Radon enters all buildings through cracks in floors, crawl spaces and service lines. Radon will enter any building regardless of its use, age, operation, the construction methods employed or the quality of construction. High radon may also be present in groundwater and will enter buildings through plumbing, particularly in buildings with water wells. Once radon has entered a building it concentrates to potentially unsafe levels and is inhaled deeply into the lungs. This internal radiation exposure increases an individual's risk of lung cancer.

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Who should be concerned about Radon?

Everyone should be aware of radon and how they, their family, employees or tenants are exposed to radon. On average Canadians spend over 90% of their time indoors (between home, work and public buildings) where radon levels may be elevated. Therefore an individual’s exposure to radon is likely never from a single source. Attention must be paid to all sources of radon exposure as there are cumulative. Ever increasing public awareness due to Health Canada’s radon awareness campaign will educate Canadians and increase concern about radon. This will add pressure for the administrators of buildings to measure and mitigate.

Bill 96, Radon Awareness and Prevention Act, 2013 was introduced September 9, 2013 and carried second reading on September 12, 2013. If passed, this bill will make radon testing mandatory in all workplaces in Ontario, with the exception of construction projects, before December 31, 2016. Failure to comply with these provisions carries maximum penalties of $25,000 or imprisonment for a term of not more than 12 months, or both for any person in contravention. A corporation convicted of an offence may face a maximum fine of $500,000.

Cancer Effects of Radon

Radon is known to cause lung cancer. According to Public Health Ontario, "13% or almost 850 lung cancer deaths each year in Ontario are attributable to radon". Studies by Health Canada attribute indoor radon exposure as "the second leading cause of lung cancer after tobacco smoking".

The safe radon exposure level provided by Health Canada is 200 Becquerels per cubic metre of air (Bq/m3). The United States Environmental Protection Agency (EPA) sets a level of 150 Bq/m3, while the World Health Organization (WHO) established a standard of no more than 100 Bq/m3.

Health Canada has estimated that about 7% cent of Canadian homes and 8.2% of Ontario homes are above the radon guideline of 200 Bq/m3. The radon potential map of Canada clearly shows the majority of southwestern Ontario in the High Risk Zone.

Health Canada has developed measurement and mitigation guidelines for various building types based primarily on function, which are summarized as follows:

Schools, Hospitals & Healthcare, Detention Centres
Residential Dwellings (Homes)
Residential Dwellings (Apartments)

How do we measure Radon?

Air testing, as prescribed by Health Canada, is conducted by deploying a small sampling canister in the lowest lived-in level of a building and leaving it undisturbed for a period of time. Depending on the sampling method used, sample durations can range from 48 hours to one year. Health Canada recommends sample durations of three to 12 months and never less than one month.

The reason for such long sample durations is to compensate for fluctuations in radon concentrations from daily and seasonal weather, occupant activity, and other inherent variables. Once sampling is complete the results are compared to the 200 Bq/m3 criterion. If the building has elevated radon concentrations, mitigation measures to reduce the concentration should be implemented within a reasonable time frame. Based on the concentration detected in the building Health Canada has established the following recommended mitigation time frames.

Radon Concentration
Greater than 600 Bq/m3
Between 200 Bq/m3 & 600 Bq/m3
Less than 200 Bq/m3
Recommended Remedial Action Time
In less than 1 year
In less than 2 years
No action required

How is elevated Radon reduced in a building?

Since each building is unique, there are several ways to mitigate radon levels. Care should be taken in the selection of methods used in order to optimizing the protection of human health with the available funds.

The most effective and perhaps preferred method of mitigation is sub-slab depressurization (SSD). A typical SSD system involves coring holes through the basement floor slab and installing draw piping and an air tight in-line fan that exhausts outdoors. A small fan generates a slight negative air pressure relative to the building interior under the floor slab. This prevents the radon from entering the building and vents it outdoors.

It has been recommended that buildings be retested every two years after a mitigation system is implemented to ensure it is operating properly. Regardless of whether or not a mitigation system is installed, retesting should be conducted whenever major renovations are performed or building operations altered.

How do you find a certified Radon professional?

Radon measurement specialists and mitigation contractors must meet an acceptable level of expertise to be granted proficiency status. the Canadian National Radon Proficiency Program ( C-NRPP) designations are proof that an individual possesses the skills and knowledge to conduct radon testing, assessment and mitigation.

Bruce Decker, C.E.T., ROHT, BSSO

Senior Technical Advisor, Building Health Sciences, QA

Mr. Decker’s qualifications as a Certified Engineering Technologist (C.E.T) in civil engineer and Building Science Specialist Ontario (BSSO) combined with his ROHT designation and Health and Safety experience qualify him as an expert in indoor air quality, soil vapour intrusion and radon. Bruce is a Certified Radon Measurement Provider under the National Environmental Health Association (NEHA) – National Radon Proficiency Program (NRPP) - Cert. No. 106349 RT; and the Canadian National Radon Proficiency Program (C-NRPP) - Certified Radon Measurement Provider - ID# 201017 CRT.

While testing his own home, it was revealed that concentrations of radon in Bruce’s basement ranged between 220 Bq/m3 to 272 Bq/m3 with a main floor concentration of 90 Bq/m3. Concentrations measured using a radon grab sampler indicated approximately 4550 Bq/m3 beneath the basement floor slab. After the installation of a sub-slab depressurization system indoor basement levels dropped to 14 Bq/m3 (close to outdoor levels) with concentrations under the floor slab holding steady at 445 Bq/m3.


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