A chemical compound with the chemical formula CH4 (one atom of carbon and four atoms of hydrogen). It is the simplest alkane and the main constituent of natural gas. At room temperature and standard pressure, methane is a colourless, odourless gas. The familiar smell of natural gas as used in homes is achieved by the addition of an odorant as a safety measure. Methane has a boiling point of −164 °C (−257.8 °F) at a pressure of one atmosphere. As a gas it is flammable over a range of concentrations (5.4–17%) in air at standard pressure.