A detailed analysis of each plausible situation resulting in fluid discharges into the flare and vent systems should be made to determine the discharge system design rates. When analyzing a single contingency, consideration of all directly related effects, which would potentially involve more than one process unit, should be made (e.g., loss of electrical power or instrument air). A routine flaring or venting event (e.g., compressor down) may be already underway when an unanticipated but related event occurs, and the cumulative impact of all flow should then be considered. Flare and vent systems should be designed for the largest single contingencies.
Furthermore, for field developments with multiple platforms having interconnecting gas pipelines, the need to depressure each pipeline through the flare system on one platform due to an incident on the other should be considered in determining the maximum load. Additionally, the controlling case for designing the platform vapor disposal system could be from an inter-field or subsea flowline if the flowline is rated at a higher pressure than the platform piping, and an inlet valve fails.