HAZOP Studies

A HAZOP is systematic about one thing: deviation from design intent. The team takes a node with a stated intent, applies guide words to flow, pressure, temperature, level and composition, and works out what causes each deviation, what it leads to and what stands in the way. That discipline is what makes it the upstream feedstock for LOPA, for SIL determination under IEC 61511, for bow tie barrier mapping and for the argument in a safety case. It also means the study needs a design firm enough to examine, which is why it belongs at detailed design rather than earlier. The value depends on three things that are easy to state and hard to hold: the independence and competence of the chair, the quality of the P&IDs and the way nodes are cut, and whether recommendations survive to close out. The failure modes are consistent across the industry, being recycle loop blindness, batch and transient modes skipped because the guide words were written for continuous flow, low frequency high consequence scenarios waved through, and human factors treated as somebody else's study.