Human exposure to radiation is often measured in rems (roentgen-equivalent man), or millirems (mrem). The cancer risk caused by exposure to radiation is through to be approximately 1 fatal cancer per 8,000 person-rems of exposure (eg –1 cancer death if 8,000 people are exposed to 1 rem each, or 10,000 people exposed to 0.8 rems each, etc.).
Natural radioactivity in the environment is thought to expose us to roughly 130 mrem/yr.