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5. Redesign: lock of manual valves to prevent hazard
• HAZOPs may not consider the mal-operation of locked valves as being
credible.
• IEC61511 refers to addressing hazards “under all reasonably foreseeable
circumstances…and reasonably foreseeable misuse”
• CCPS
[7]
and other sources quote suggest risk reduction possible from LO/LC
valves plus procedure.
• However, we should definitely not consider that a LO/LC valve is a fool-proof
solution. It’s a safeguard which has a probability of failure.
• Key interlocking systems can be seen as having a higher reliability (including
less prone to abuse)
Ref [7] CCPS – Layer Of Protection Analysis