Functional Safety 2016

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