Passive systems of reduction have been revealed to be capable of reducing interior radon levels by greater than 50%. When radon ventilation fans are included radon levels can also be decreased better. The danger of lung cancer cells boosts by 16% per 100 Bq/m3 rise in long time ordinary radon focus. The dose-response connection is straight-- for instance, the danger of lung cancer cells boosts proportionally with increasing radon direct exposure. The lower the radon concentration in a residence, the lower the danger of lung cancer cells as there is no known threshold listed below which radon exposure brings no danger.