Radon, a radioactive element
Radon is the major source of human exposure to radioactivity. This would account for 16% of lung cancer deaths in Canada.
Radon can be concentrated in poorly ventilated crawl spaces and/or basements. With a half-life of 3.8 days, significant quantities can only penetrate into buildings through breaches in the concrete such as joints, cracks in slabs, drains or sumps. Once infiltrated, radon remains in poorly ventilated areas.
The concentration of radon in a building can be reduced by aeration and ventilation, sealing of cracks in the concrete, and, in more serious cases, depressurization of the soil under the basement slab.