Flare Radiation Plot and isopleths map
Flares in oil and gas production or processing plants continuously burn hydrocarbon gases. The flame of this burning of gases emits heat, a part of which is transferred to the surroundings by radiation of heat. The fraction of heat generated being radiated to the surroundings is known as emissivity coefficient for the flame. The radiated heat energy reaches different surrounding locations at different intensities, depending on the distance of a particular location from the flame. Flare radiation plots are representative of the incident radiated heat from flare reaching at different locations in the surroundings.
Flare radiation plots typically consist of isopleths. Isopleths are curves on a map of the flare surroundings which connect geographical points receiving the same intensity of heat radiated from the flare.
Isopleths are useful when designing the manned facilities surrounding the flare. As per API RP 521 (Pressure-Relieving and Depressuring Systems), radiation intensity level of 1.58 kW/m² is generally known as continuous full shift exposure. API RP 521 allows personnel with appropriate clothing to be continuously exposed to this radiation level.
Outside of the radiation isopleths corresponding 1.58 kW/m2, personnel with appropriate clothing may be continuously exposed. A radiation intensity level of 4.73 kW/m² would be the limit in areas where emergency actions lasting two to three minutes may be required by personnel without shielding but with appropriate clothing. A radiation level of 6.31 kW/m² would be the limit in areas where emergency actions lasting up to 30 seconds may be required by personnel without shielding but with appropriate clothing.
Isopleths corresponding to these levels are developed prior to designing the operation facilities in the flare surroundings.