Natural gas tens of millions of structures that use the fuel, the individual risk of using natural gas is very low. Natural gas heating systems may cause carbon monoxide poisoning if unvented or poorly vented. In 2011, natural gas furnaces, space heaters, water heaters and stoves were blamed for 11 carbon monoxide deaths in the US. Another 22 deaths were attributed to appliances running on liquified petroleum gas, and 17 deaths on gas of unspecified type. Improvements in natural gas furnace designs have greatly reduced CO poisoning concerns. Detectors are also available that warn of carbon monoxide and/or explosive gas (methane, propane,
Natural gas prices import gas based on the Henry Hub index, which was, until very recently, the most widely used reference for US natural gas prices. Depending on the marketplace, the price of natural gas is expressed in US dollars (or other currency) per 1 million British thermal units (MMBtu), thousand cubic feet (Mcf), or 1,000 cubic meters. Note that, for natural gas price comparisons, $ per MMBtu multiplied by 1.025 = $ per Mcf of pipeline-quality gas, which is what is delivered to consumers. For rough comparisons, one million Btu is approximately equal to a thousand cubic feet of natural gas. Pipeline-quality