A gas flare, alternatively known as a flare stack, flare boom, ground flare, or flare pit, is a gas combustion device used in places such as petroleum refineries, chemical plants and natural gas processing plants, oil or gas extraction sites having oil wells, gas wells, offshore oil and gas rigs and landfills. Wikipedia

1) Flares use open flames during normal and/or emergency operations to combust hazardous gaseous. The system has no special features to control temperature or time of combustion; however, supplemental fuel may be required to sustain the combustion. Historically, flares have been used to dispose of waste gases in the oil and gas industry and at wastewater treatment plants having anaerobic digestors. Regulation for thermal destruction of hazardous wastes limit the practical use of flaring to combustion of relatively simple hydrocarbons, such as methane from digesters or landfill gas collection systems. 2) A control device that burns hazardous materials to prevent their release into the environment; may operate continuously or intermittently, usually on top a stack. OmegaWiki