pressure equipment. A cold relief drum which is segregated from wet relief system because of the risk of freezing. A water seal drum to prevent any flashback of the flame from the top of the flare stack. An alternative gas recovery system for use during partial plant startups and shutdowns as well as other times when required. The recovered gas is routed into the fuel gas system of the overall industrial plant. A steam injection system to provide an external momentum force used for efficient mixing of air with the relieved gas, which promotes smokeless burning. A pilot flame (with its ignition system) that burns all the time so that it is available to ignite relieved gases when needed. The flare stack, including a flashback prevention section at the upper part of the stack. The schematic shows a pipe flare tip. The flare tip can have several configurations: a simple pipe flare a sonic tip – upstream pressure > 5 bar a multi nozzle tip, sonic or subsonic a Coanda tip – a profiled tip using the Coanda effect to entrain air into the gas to improve combustion. Flare stack height The height of a flare stack, or the reach of a flare boom, is determined by the thermal radiation that is permissible or tolerable for equipment or personnel to be exposed to. For continuous exposure of personnel wearing appropriate industrial clothing a maximum radiation level of 1.58 kW/m2 (500 Btu/hr.ft²) is recommended. Higher radiation levels are permissible but for reduced exposure times: 4.73 kW/m2 (1500 Btu/hr.ft²) would limit exposure to 3 to 4 minutes 6.31 kW/m2 (2000 Btu/hr.ft²) would limit exposure to 30 seconds. Ground flares Ground flares are designed to hide the flame from sight and to reduce thermal radiation and noise. They comprise a steel box or cylinder lined with refractory material. They are open at the top and have openings around the base to allow combustion air to enter. They may have an array of multiple flare tips to provide turndown capability and to spread the flame across the cross-section of the flare. They are generally used onshore in environmentally sensitive areas and have been used offshore on floating production storage and offloading installations (FPSOs). Crude oil production flares When petroleum crude oil is extracted and produced from oil wells, raw natural gas associated with the oil is brought to the surface as well. Especially in