How do you size a pressure relief system?

Relief system sizing: (1) Identify scenarios - fire, blocked outlet, cooling failure, runaway reaction, tube rupture, control valve failure, thermal expansion. (2) Calculate relief load for each scenario - mass flow rate and required orifice area using API 520/521. (3) Select controlling scenario (largest relief rate). (4) Size relief device - orifice area from API equations considering back pressure. (5) Design inlet piping - pressure drop less than 3% of set pressure. (6) Design outlet piping - calculate back pressure, ensure below device limits. (7) Disposal system - flare, scrubber, or atmosphere depending on fluid. Document all scenarios and calculations for future verification and regulatory compliance.