Functional Safety 2016

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