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In our day to day practice we frequently see risk/hazard methodologies being stretched to «fit the clients’ case», or, in other words, tools being selected to deliver results they were not designed for. This is a brief summary for HAZOP, a common process hazard identification methodology. In the coming weeks we will review several of these methodologies and will end the review with a comparison.
HAZOP is a structured and systematic examination of a planned or existing process or operation (the system) in order to identify and evaluate problems (HAZards) that may endanger personnel or equipment, or prevent efficient operation; it should be carried out by a suitably experienced multi-disciplinary team (HAZOP team) during a set of meetings. During the meetings the system is broken down into detailed elements (often down to single pipe and valve) and hazards are defined in terms of malfunctions defined thanks to guide-words lists including, for example: No or not, Other than, More, Early, Less, Late, As well as, Before, Part of, After, Reverse (of intent), Others can be crafted as needed…
HAZOP is a Hazard identification tool: it is very top-heavy and works well for processes.
HAZOP identifies and evaluates hazards (malfunctions), but not risks (probability of an adverse event and its consequences). HAZOP is blind to hazards that occur outside of the system under analysis and could impact the system, until a malfunction is detected. Also it does not prioritize hazards and therefore in the decision making process the same weight may be given to two items which might generate very different risks. HAZOP is mostly used in process intensive hazardous industries, but remains a rare sight in main stream application.
For the curious here is a small example of the time required:
An Ethylene plant has 110 P&IDs, 600 equip’t items. 600 items
Consider Pressure, Temperature, Flow Composition and Function, i.e. 5 variables
Consider these guide-words: None, More of, Less of Part of, More than and Other than. i.e. 6 guide words
Questions to be answered =600*5*6=18,000
Consider 5 minutes per question
Time for detailed ethylene plant HAZOP study = 5*18,000= 90, 000 minutes @ 4 hours, 240 minutes sessions per day = 375 Days
Days per week = 5 days/week No. of weeks to complete HAZOP for plant = 75weeks