“…Building materials, water and natural gas are additional sources of indoors radon. Radon escapes through the cracks and pores of the soil and rocks in the earth's crust, then it seeps to the indoors air by a variety of factors such as: the difference in air pressure inside and outside the house, cracks, pores, holes in the basement of the house, the type of the soil, soil permeability, soil moisture content, porosity, and the uranium content of soil (Ennemoser et al, 1995).…”