Hazardous inert gas is a term used to describe a type of gas that is not reactive and can be dangerous if inhaled. RADON (5 letters) is one example of a hazardous inert gas. RADON is a naturally occurring radioactive gas that is colorless, odorless, and tasteless. It is produced by the breakdown of uranium in soil, rock, and water and can accumulate in buildings and homes. Exposure to high levels of RADON can cause lung cancer and other health problems.