What more can be said about HAZOP, a mature subject well developed since the 1960’s? Those practitioners who have worked their way through one hundred or more P&ID’s, taking several weeks, will understand how difficult it is to keep the team focused and avoid “analysis paralysis”.

Starting each line with a failure effects review has several benefits. Most causes generated by the traditional guidewords are captured at this stage, and the team must do some solid analysis from the start improving their understanding of the line dynamics before the classical guidewords are applied. The quality of the finished product, namely the HAZOP report, in the author’s opinion, is greatly improved. One disadvantage is that lateral thinking can be inhibited. It is suggested however, that not much lateral thinking goes on in practice, after a few days HAZOP’ing.

The addition of failure effects to the HAZOP process will be demonstrated by example. This will include deviations to be addressed in typical control systems (switches, transmitters, protection devices) and process equipment items. For example, how can a measurement offset (high or low) affect a control system or protection device? Can this lead to a failure on demand and what will be the consequence? The thought process can be interesting, particularly with complex control loops. Those familiar with instrumented protection (IPF) reviews will recognise these questions and the relationship to safety integrity level (SIL) determination which can be incorporated into the review if required.