When Maureen Hayes first tested her Ottawa home for radon a little over a year ago, the initial reading was far below Canada's current threshold to take action.

Her device showed 114 becquerels per cubic metre (Bq/m³), well under the 200 Bq/m³ guideline for hiring a radon professional, according to Health Canada's guidance .

But Hayes soon realized the country's recommended limit for this invisible, cancer-causing radioactive gas is actually double that of the World Health Organization (WHO). And as she kept testing, she saw her home's levels hit 180 Bq/m³ and beyond — still under Canada's threshold yet firmly above the WHO's guideline.

Hayes was concerned — and confused. "The government issues these guidelines," she said, "but they're different internationally."

After seeing CBC News coverage on radon earlier this year, Hayes decided to install a $3,000 mitigation system to slash her home's radon levels and, in turn, reduce any exposure that might heighten her risk of lung cancer.…