A hazard and operability study (HAZOP) is a structured and systematic examination of a complex system, usually a process facility or machinery, in order to identify hazards to personnel, equipment or the environment, as well as operability problems that could affect operations efficiency. It is the foremost hazard identification tool in the domain of process safety. The intention of performing a HAZOP is to review the process or machinery through all phases of the product lifecycle to pick up design and engineering issues that may otherwise not have been found in other hazard identification (risk assessments) or design tools (FMEA’s, FTA’s, etc.) The technique is based on breaking the overall complex design of the process into a number of simpler sections called nodes which are then individually reviewed. It is carried out by a suitably experienced multi-disciplinary team (roles defined in section below) during a series of meetings. The HAZOP technique is qualitative and aims to stimulate the imagination of participants to identify potential hazards and operability problems. Structure and direction are given to the review process by applying standardized guideword prompts to the review of each node. A relevant standard IEC 61882 calls for team members to display 'intuition and good judgement' and for the meetings to be held in "an atmosphere of critical thinking in a frank and open atmosphere [sic]." The HAZOP technique was initially developed for systems involving the treatment of a fluid medium or other material flow in the process industries, where it is now a major element of process safety management. It was later expanded to the analysis of batch reactions and process plant operational procedures. Recently, it has been used to assess domains other than or only loosely related to the process industries, namely: software applications including programmable electronic systems; software and code development; systems involving the movement of people by transport modes such as road, rail, and air; administrative procedures in different industries; medical devices; machinery; etc.
History The technique is generally considered to have originated in the Heavy Organic Chemicals Division of Imperial Chemical Industries (ICI), which was then a major British and international chemical company. Its origins have been described by Trevor Kletz, who was the company's safety advisor from 1968 to 1982. In 1963 a team of three people met for three days a week for four months to study the design of a new phenol plant, starting with a technique called critical examination which asked for alternatives but later changed this to ask for deviations. The method was further refined within the company, under the name operability studies, and became the third stage, detailed design, of its hazard analysis procedure (the first two stages being done during conception and specification). In 1974 a one-week safety course including this procedure was offered by the Institution of Chemical Engineers (IChemE) at Teesside Polytechnic. Coming shortly after the Flixborough disaster, the course was fully booked, as were ones in the next few years. In the same year as the 1974 course offering, the first paper in open literature was also published. In 1977 the Chemical Industries Association published a guide. Up to this time the term 'HAZOP' had not been used in formal publications. The first to do this was Kletz in 1983, with what were essentially the course notes (revised and updated) from the IChemE courses. By 1983, hazard and operability studies had become an expected part of chemical engineering degree courses in the UK. Nowadays, government regulators (EPA, OSHA, etc.) and the process industry at large (including operators and contractors) consider HAZOP a strictly necessary step of project development, at the very least during the detailed design phase.
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