Carbon monoxide, chemical formula CO, is a colorless, odorless, tasteless, flammable and highly toxic gas. It is a major product of the incomplete combustion of carbon and carbon-containing compounds. It is less dense than air under ordinary conditions, however it accumulates on the ground, meaning that if poisoning causes loss of consciousness the amount of carbon monoxide inhaled increases and so fatality is radically increased. It is very slightly soluble in water and burns in air with a characteristic blue flame, producing carbon dioxide; it is a component of producer gas and water gas, which are widely used artificial fuels. It is a reducing agent, removing oxygen from many compounds and is used in the reduction of metals, e.g., iron , from their ores. At high pressures and elevated temperatures it reacts with hydrogen in the presence of a catalyst to form methanol. Carbon monoxide is formed by combustion of carbon in oxygen at high temperatures when there is an excess of carbon. It is also formed with a byproduct oxygen by decomposition of carbon dioxide at very high temperatures (above 2,000 °C). It is present in the exhaust of internal-combustion engines, often the exhaust of automobiles, and is generated in coal stoves, furnaces, and gas appliances that do not get enough air. This may be due to insufficient ventilation or other reasons.