Aliphatic Hydrocarbon Gases
Ethane is an odourless gas which is used as a refrigerant and as a component of natural gas. It is methane (swamp gas), however, which is the major component of natural gas. Both are odourless gases and produce simple asphyxiation at high concentrations. Conversion of domestic gas from coal gas (mostly carbon monoxide) to natural gas (mostly methane) has significantly reduced mortality from domestic gas leaks, since methane is much less toxic as compared to carbon monoxide. Methane being odourless, a stenching agent (alkyl mercaptan) is deliberately added to domestic gas so that leaks can be immediately recognised. It is important to remember that a build-up of methane resulting in 4.8 to 13.5% concentration in air constitutes an explosive mixture which can be ignited by a flame or even a tiny spark. Most explosions in mines (as well as homes using natural gas as fuel) occur because of this reason.
Butane, liquefied petroleum gas, propane, and propylene have a faint petroleum-like odour and may be stenched with mercaptans for transport and storage. Butane is used as a raw material for automobile fuels, in organic synthesis, and as a solvent, refrigerant, and aerosol. Propane is used as a raw material in organic synthesis, as a component of industrial and domestic fuels, as an extractant, a solvent, and a refrigerant, and in the manufacture of ethylene. Incomplete combustion of these agents can release carbon monoxide into the ambient air. Butane is often abused by adolescents in the form of inhalation.
Liquefied petroleum gas is used as a domestic, industrial, and automotive fuel. Propylene is a raw material in polypro-pylene, isopropyl alcohol, isopropylbenzene, acetone, and propylene oxide manufacturing.
Most of the aliphatic hydrocarbon gases act as simple asphyxi-ants (vide supra), in addition to additional specific toxicities.