 Because radon has a similar pressure and temperature curve to propane, and oil refineries separate petrochemicals based on their boiling points, the piping carrying freshly separated propane in oil refineries can become radioactive because of decaying radon and its products.Residues from the petroleum and natural gas industry often contain radium and its daughters.The sulfate scale from an oil well can be radium rich, while the water, oil, and gas from a well often contains radon.