HAZOP stands for HAZard and OPerability study and is a safety assessment technique developed at the Imperial Chemical Industries (ICI) company during the 1960s for application to chemical and similar process plants. It seeks to uncover hazardous states which the plant could conceivably enter, thereby providing a basis on which to develop a safety strategy for the plant design and operation. The technique involves a team of people systematically examining design drawings, traditionally 'Piping and Instrumentation Diagrams', and investigating postulated departures from design intent. As such, the technique is best characterised as one of creative search, relying on the interaction between knowledgeable people within the team and on the use of guide words ('no', 'more', 'less', etc.) applied to attributes of the components in the design, particularly flows, to identify plausible anomalous conditions. Publications in the U.K. by the Chemical Process Industries Association and Kletz have popularised the technique in these industries.
Chudleigh and Catmur, along with other groups, have been investigating the application of the HAZOP technique to software-based systems for several years, dating back at least to their paper in SAFECOMP '92. Similar guide words are applied to the flow-type entities appearing in software design descriptions, such as those in data flow diagrams and the transitions of state transition diagrams. The HAZOP technique has been adopted in a draft military standard in the U.K.