There really is no safe level of Radon exposure. However, with that being said, there are recommended guidelines for exposure limits set forth from Government and Health agencies. Health Canada recommends the following:
Radon gas is measured in Canada as Becquerels per cubic meter (Bq/m³) or in the US as picoCuries per liter (pCi/L). The current airborne radon level at which Health Canada recommends action is 200 Bq/m³ or 5.4 pCi/L. The US EPA guidelines are set at 4 pCi/L or 148 Bq/m³ the World Health Organization (WHO) guideline is set at 100 Bq/m³ or 2.7 pCi/L. These are all recommended guidelines and, the best advise is to obtain the lowest level of airborne radon you can within your financial limit.
Radon concentrations in water can also be a concern and contribute to airborne Radon levels. High Radon in water levels are usually associated with deep water wells. Hot water “vapourizes” into the air by converting into steam and thus becomes an inhalation hazard of radon into the lungs. As a general rule, a measurement of 10,000 Bq/m³ of Radon in water will contribute roughly 1.0 Bq/m³ throughout the household air. This may also vary depending on the amount of water used, the air exchange rate of the building, and how much hot water / steam is created or used.
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