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2. Process Safety Time – Terms of Reference
PST is modelled to be when the hazardous event occurs, which can be
interpreted to mean:
• Exceed design Pressure
• Prevent PSV lift
• Exceed Design pressure +15%
• Even exceed test pressure (not recommended)
Basis in terms of:
• Worst case levels in vessels; process conditions
• If PCV fail open is the cause, assume failed to 100% open.
• No help from PCVs or other PID control
• No help from PSVs