the biological process. There are two types of gas flare used for controlling biogas, open or enclosed. Open flares burn at a lower temperature, less than 1000 °C and are generally cheaper than enclosed flares that burn at a higher combustion temperature and are usually supplied to conform to a specific residence time of 0.3s within the chimney to ensure complete destruction of the toxic elements contained within the biogas. Flare specification usually demands that enclosed flares must operate at >1000 °C and <1200 °C; this in order to ensure a 98% destruction efficient and avoid the formation of NOx. Adverse health effects Flares release a cocktail of chemicals known to be harmful to human health, including benzene, particulates, nitrogen oxides, heavy metals, black carbon, and carbon monoxide. Several of these pollutants correlate with preterm birth and reduced newborn birth weight. Pregnant women living near flaring natural gas and oil wells experienced a 50% greater premature birth rate. Flares may emit methane and other volatile organic compounds as well as sulfur dioxide and other sulfur compounds, which are known to exacerbate asthma and other respiratory disease. A 2021 study found that a 1% increase in flared natural gas increases the hospitalization rate by 0.73%. Environmental impacts The natural gas that is not combusted by a flare is vented into the atmosphere as methane. Methane's estimated global warming potential is 28-36 times greater than that of CO2 over 100 years, and 84-87 times greater over 20 years. Therefore, to the extent that gas flares convert methane to CO2 before it is released into the atmosphere, they reduce the amount of global warming that would otherwise occur. However, flaring emissions contributed to 270 Mt (megatonnes) of CO2 in 2017 and reducing flaring emissions is key to the mitigation of global warming. An increasing number of governments and industries have pledged to eliminate flaring. The Global Methane Pledge signed at COP26, in which 111 nations committed to reducing methane emissions by at least 30 percent from 2020 levels by 2030, is also playing a role in raising the global focus on methane. Additional noxious fumes emitted by flaring may include, aromatic hydrocarbons (benzene, toluene, xylenes) and benzo(a)pyrene, which are known to be carcinogenic. A 2013 study found that gas flares contributed over 40% of the black carbon deposited in the Arctic, thus further increasing the rates of snow and ice melt. Flaring can