The Hazard and Operability (HAZOP) review is a systematic way to identify hazards to staff, facilities, and the environment. It may be applied to many types of plant ranging from large continuous processes such as petrochemical plants, to small batch ones such as autoclaves or machines for forming plastic.
The technique was developed in Mond Division of ICI in the 1960's and spread throughout ICI and to other parts of the UK and European Process Industries. The UK Chemical Industries Association, the Dutch Process Safety Committee, and the German Industrial Insurance Institute for the Chemical Industry, to name a few have published standards based on the HAZOP method.
The HAZOP technique involves the use of "Guide Words" to stimulate an imaginative yet systematic search by the investigative team for possible hazards and operational difficulties. This is typically done in a series of "Examination Sessions" where P&IDs, Sequence of Operations and other detailed process specification documents are reviewed for hazards by asking questions such as what would happen in the event of "higher than expected flow", "lower than expected flow", "no flow", or "reverse flow".
There are a number of HAZOP aids available including documentation, training materials and computer programs.