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In any chemical process industry, the implementation of flare system involves a significant amount of investment in terms of capital cost. There is a significant opportunity to optimize the flare design by applying High-Integrity Protection System (HIPS). HIPS has been widely used as one of mitigation strategies in reducing the flare capacity for new and existing plant as this being allowed by API Std 521. For a new refinery complex, HIPS was introduced in a total of five (5) column reboilers in order to safely reduce the acid gas flare design capacity. Based on preliminary analysis, partial power failure scenario had been identified as the governing scenario for the acid gas flare design capacity. In this use case, HIPS will mitigate any potential overpressure scenario by cutting off the steam supply to the distillation column reboilers. However, it is important to consider the transient relief from the columns to the acid gas flare system considering this may affect the design capacity of the flare. The total transient relief rate estimated from dynamic simulation accounts for the amount of vapor generated due to residual heat from the reboiler after HIPS valves were closed and loss of reflux to the distillation column. The outcome of the model were time-series plots, detailing out the individual and total relieves of all the distillation columns. This paper presents a case study on relief load calculation with HIPS installation and consideration of transient effect for five columns before activation of HIPS together. [ABSTRACT FROM AUTHOR]