A gas flare or flare stack is an elevated vertical stack or chimney found on oil wells or oil rigs, and in refineries, chemical plants and landfills used for burning off unwanted gas or flammable gas and liquids released by pressure relief valves during unplanned over-pressuring of plant equipment.(1)(2)(3) In landfills, the primary purpose of this device is to vent and/or burn waste gas which results from the decomposition of materials in the dump.