Colorless; odorless; very toxic gas; CO; burns to carbon dioxide with a blue flame. Formed as a product of the incomplete combustion of carbon (such as in water gas and producer gas; in the exhaust gases from internal-combustion engines, such as automotive; and in the gases from the detonation of explosives). Used chiefly in the synthesis of carbonyls (such as nickel carbonyl in the refining of nickel), phosgene, and many organic compounds (such as hydrocarbons for fuels, methanol and higher alcohols, aldehydes, and formates). This gas is formed during mine fires and after explosions.