Butane lighters have a valved orifice that meters the butane gas as it escapes. Gaseous hydrocarbons such as mixtures of pentane, propane, butane and isobutane took their place. Notable examples of asphyxiant gases are methane, nitrogen, argon, helium, butane and propane. LPG (propane/butane) or fuel oil may be used where natural gas is not available. Some gases, such as propane and butane gases, are inhaled directly from the canister. The plant produces natural gas liquids (NGL) including propane, butane, and condensate products. It also contains small amounts of ethane, propane, butane, some heavier alkanes, and nitrogen. It also places levies on natural gas, pump gas, propane, butane, and aviation fuel. Indoors, exposure arises from cigarette smoke, and butane and kerosene heaters and stoves. It is a mixture of propane and butane. They can operate on electricity, propane, bottled butane (small units), or natural gas. The explosive TATP and 120 canisters of butane and propane were found inside the house. The price of propane, butane and aviation fuel will also increase. Propane/butane blends are also listed in these specifications. In a similar manner, propane and cyclopropane, butane and cyclobutane, etc.