- Hazard and operability study
Hazard and operability studies are a methodology for identifying and dealing with potential problems in industrial processes, particularly those which would create a hazardous situation or a severe impairment of the process. It is commonly known as HAZOPKletz, T. A., (1983) "HAZOP & HAZAN Notes on the Identification and Assessment of Hazards" IChemE Rugby] . Some authors call it Hazard and Operability Analysis [e.g. Center for Chemical Process Safety (1992) "Guidelines for Hazard Evaluation Procedures - With Worked Examples" (2nd Edition). AIChE. ISBN 978-0-8169-0491-4] . It is said to be the most widely used method of
hazard analysisin the process industriesWells, G., (2004) "Hazard Identification and Risk Assessment", IChemE ISBN 0852954638] , notably the chemical, petrochemical and nuclear industries.It is the subject of an international standardBritish Standard BS: IEC61882:2002 "Hazard and operability studies (HAZOP studies)- Application Guide" British Standards Institution. “This British Standard reproduces verbatim IEC 61882:2001 and implements it as the UK national standard.”] and is listed as a “suitable methodology” in US Federal Regulations [ 29 CFR1910, 29 CFR1926, 40CFR68] .
The method applies to processes (existing or planned) for which design information is available. This commonly includes a
Process flow diagram, which is examined in small sections, such as individual items of equipment or pipes between them. For each of these a design Intention is specified. For example, in a chemical plant, a pipe may have the intention to transport 2.3 kg/s of 96% sulfuric acid at 20°C and a pressure of 2 bar from a pump to a heat exchanger. The intention of the heat exchanger may be to heat 2.3 kg/s of 96% sulfuric acid from 20°C to 80 °C. The Hazop team then determines what are the possible significant Deviations from each intention, feasible Causes and likely Consequences. They then propose possible modifications to the design to remove or reduce the risk of the deviation or reduce the consequences.Usually, the designers consider these suggestions, and produce a modified design, which is subject to a further Hazop. The process may be repeated until it is considered no further modifications are needed.
A Hazop meeting is generally scheduled for 3 hours. For a medium-sized chemical plant where the total number of items to be considered is 1200 (items of equipment and pipes or other transfers between them) about 40 such meetings would be neededSwann, C. D., & Preston, M. L., (1995) "Journal of Loss Prevention in the Process Industries", vol 8, no 6, pp349-353 "Twenty-five years of HAZOPs"] .
Parameters and guide words
The key feature is to select appropriate parameters which apply to the design intention. These are general words such as Flow, Temperature, Pressure, Composition. In the above example, it can be seen that variations in these parameters could constitute Deviations from the design Intention. In order to identify Deviations, the Study Leader applies (systematically, in order) a set of Guide Words to each parameter for each section of the process. The current standard Guide Words are as follows:
In earlier publications it was suggested that the Study Leader could also be the Recorder but separate roles are now generally recommended. A minimum team size of 5 is recommended Nolan, D.P. (1994) "Application of HAZOP and What-If Safety Reviews to the Petroleum, Petrochemical and Chemical Industries". William Andrew Publishing/Noyes. ISBN 978-0-8155-1353-7] . In a large process there will be many Hazop meetings and the team may change as specialists are brought in for different areas, and possibly different members of the design team, but the Study Leader and Recorder will usually be fixed. As many as 20 individuals may be involved but is recommended that no more than 8 are involved at any one time. Software is now available from several suppliers to aid the Study Leader and the Recorder.
The technique originated in the Heavy Organic Chemicals Division of
ICI, which was then a major British and international chemical company. The history has been described by Trevor KletzKletz, T., (2000) "By Accident - a life preventing them in industry" PVF Publications ISBN 0-9538440-0-5] who was the company's safety advisor from 1968to 1982, from which the following is abstracted.
1963a team of 3 people met for 3 days a week for 4 months to study the design of a new Phenolplant. They started with a technique called "critical examination" which asked for alternatives, but changed this to look for deviations. The method was further refined within the company, under the name "operability studies", and became the third stage of its hazard analysisprocedure (the first two being done at the conceptual and specification stages) when the first detailed design was produced.In 1974a 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 the first paper in the open literature was also published [Lawley, H. G.,(1974) "Chemical Engineering Progress", vol 70, no 4 page 45 "Operability studies and hazard analysis" AIChE] . In 1977the Chemical Industries Associationpublished a guide [Chemical Industries Association (1977) "A Guide to Hazard and Operability Studies"] . 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 this time, hazard and operability studies had become an expected part of chemical engineeringdegree courses in the UK.
Kletz, Trevor|title=Hazop and Hazan|edition=4th Edition|publisher=Taylor & Francis|year=2006|id=ISBN 978052955062
*cite book|author=Tyler, Brian, Crawley, Frank & Preston, Malcolm|title=HAZOP: Guide to Best Practice|edition=2nd Edition|publisher=IChemE, Rugby|year=2008|id=ISBN 9780852955253
* [http://www.hse.gov.uk/research/hsl_pdf/2005/hsl0558.pdf Gould, J., (2000) "Review of Hazard Identification Techniques", HSE]
* [http://www.uscg.mil/hq/g-m/risk/e-guidelines/hazop.htm Summary of Hazop] Explanation by the US
* [http://www.lihoutech.com/hzp1frm.htm Hazard and Operability Studies] Explanation by a software supplier
Hazard Analysis and Critical Control Points
Process Safety Management
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