Passive systems of reduction have been shown to be capable of minimizing interior radon levels by greater than 50%. When radon ventilation followers are included radon degrees can also be reduced even more. The danger of lung cancer cells rises by 16% per 100 Bq/m3 rise in long period of time typical radon focus. The dose-response relation is linear-- for example, the threat of lung cancer cells enhances proportionally with increasing radon exposure. The lower the radon concentration in a house, the lower the danger of lung cancer cells as there is no recognized limit listed below which radon direct exposure carries no danger.