What is radon?
Radon gas is a naturally occurring, very dense, invisible, odourless, tasteless radioactive gas and it is a recognized danger to health. It’s produced as a progeny (by-product) when uranium, thorium, and radium decay (break down) in soil, rock, and water. Within the decay chain, uranium becomes thorium, which becomes radium and finally radon. Radon gas progeny then forms a solid dust-like substance that collects on surfaces and can be breathed into the lungs and ingested in water. Radon gas comes from the ground and it moves freely everywhere. It accounts for most of a person’s lifetime exposure to radiation. Radon is second only to smoking as a contributing factor to lung cancer and potentially leads to other cancers such as blood cancer. Health Canada estimates that 16% of lung cancer deaths in Canada are attributable to radon exposure. Most people don’t give radon much thought, but they should check their environment and mitigate the risk of exposure.
What level of radon is safe?
Two common measurement units for radon are “becquerel per cubic meter” (Bq/m3) and “picocurie per liter” (pCi/L). The USA standard unit is pCi/L and Bq/m3 is standard elsewhere including Canada. For conversion, 1 pCi/L is equivalent to 37 Bq/m3. Recommended safe amounts of radon tend to fall within a range rather than an agreed-upon single number. In 2009, the World Health Organization (WHO) suggested a manageable limit of 100 Bq/m3 (2.7 pCi/L) for residential radon and an absolute maximum limit of 300 Bq/m3 (8.1 pCi/L). However, the US EPA states that radon readings as low as 74 Bq/m3 (2.0 pCi/L) should have you seriously think about taking action for protection. The European Union and other agencies have their own recommended levels, which tend to average around 148 Bq/m3 (4.0 pCi/L). In Canada, acceptable levels of radon in "dwellings" which include homes or public buildings (schools, daycares, hospitals, long- term care facilities, etc.) is 200 Bq/m3 based on the Government of Canada Radon Guideline and this isn’t sufficient. The David Suzuki Foundation recommended that Health Canada should establish a new guideline for radon in the indoor air of 100 Bq/m3 and that indoor radon concentration should be reduced to as low as reasonably achievable below this level, in keeping with the principle of optimization of protection. Health Canada should also clarify that the standard applies generally to indoor air, including workplaces and public-access buildings, in addition to dwellings. Indoor radon concentrations are almost always higher than outdoor concentrations. Once inside a building, radon gas cannot easily escape without proper ventilation. Modern sealing of buildings to conserve energy reduces the intake of outside air and worsens the situation. Radon is drawn into buildings because the air pressure inside is usually lower than in the ground beneath. Plumbing drains, foundation and slab cracks, and gaps around pipe penetrations, and other openings provide points of entry to a building despite better sealing practices. The concentration of radon and radon progeny in the indoor air depends on the amount of radium in the foundation and nearby soil and how easily the radon it produces can move through soil and building walls where it can then mix with the room air. Many factors affect radon gas emission from the ground and its accumulation in the building air levels including shifting climatic conditions, temperature, atmospheric pressure, precipitation, and even construction or reconstruction. Experts recommend testing for radon during the colder months because radon levels are historically found to be higher, but there are no clear reasons why. The main cause for rising levels likely is that we are shutting our windows when it's cold. Radon progeny have very short radioactive half-lives ranging from a fraction of a second to 27 minutes. Radon progeny are present in significant quantities only if radon is present. If all the radon gas is removed, the radioactivity of radon progeny will diminish fast. However, this does not typically happen indoors because as old radon decays new radon continuously comes out from the decaying radium present in the ground and walls. Good ventilation will minimize radon gas concentrations.
Testing for radon. It is near impossible to escape exposure to radon gas in daily life, but you can take action to limit exposure. You should first have the building monitored for radon over at least three months. There are single-use test kits for this that typically cost between CAD$30 to CAD$150, however, I recommend a constant radon detection device. I use the AirThings Wave from Norway, a continuous detector with long-term and short-term averages that provides reports and real-time conditions via a phone app. At CAD$250 per unit, it's not inexpensive, but it works reliably well and you can eventually move it to different locations in a building for ongoing testing in intervals of three months or more. Large buildings would test for results better by using multiple units.
Radon mitigation.
After monitoring and finding out your radon levels, you may find that you might need to resolve consistent high readings. A Sub-Slab Depressurization (SSD) System is a very effective radon mitigation technique used in new house construction and can also be done in a retrofit at a higher cost of about $3,000. For an SSD System installation, a pipe is inserted into the sub-slab fill and an electric fan draws out and vents radon gas to the outdoors above a roof-line. It thus lowers air pressure beneath the concrete slab preventing radon from being drawn into the building. Complementary techniques include sealing all openings and cracks in the slab and foundation walls.
In large buildings (i.e., multi-residential, institutional), there will be soil and hydrology testing in preparation for foundation construction. Often, to prevent water infiltration into a foundation, a sealed bathtub (tank) outer-foundation is first constructed. The main foundation construction follows inside. With a well-engineered and designed energy-efficient HVAC system such as our TRAK Smart Energy System (SES), the building’s interior air changes are constant and this will significantly help minimize radon accumulation.
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