1. Specified IPL response time is NOT THE SAME as process safety time or the estimated response time for an IPL 2. IPL response time specification requires understanding - The effect of the deviation on the process - Whether there is process lag after the safety action is complete - How fast the function is capable of acting, including the impact of specified accuracy - The desired balance between the normal operating limit and the least conservative setpoint 3. Multiple techniques can be used to understand the process safety time - Expert judgement - Extrapolation - Mass and energy balances - First principle process modeling 4. During detailed design, usually need to correct the initial assumptions used during H&RA and conceptual design 5. ALWAYS document operating limits and assumed parameters to facilitate future MOC.
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