Radon outlet pipe on the outside wall of a public library. Radon is a radioactive gas produced by the decay of the small amounts of uranium found naturally in all rocks and soil. Levels of radon differ with different geological conditions. In areas with high levels it needs to be prevented from accumulating inside buildings. Radon is removed by using a sump. The sump consists of a pipe, running from beneath a solid floor to the outside, with a small fan in it to suck the radon from the building. Exposure to radon increases the risk of developing lung cancer.