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HAZOP is an abbreviation for HAZard and OPerability analysis. Originally developed for use at manufacturing facilities such as oil refineries, offshore oil platforms, petrochemical and chemical plants, natural gas processing plants and power plants, its application has expanded to other areas as well. It is a systematic method for examining complex facilities or processes to find actual or potentially hazardous procedures and operations so that they may be eliminated or mitigated. HAZOP Studies are performed by a team consisting of plant operators, engineers, managers and others, some of whom should be intimately familiar with the facility being studied.

Additional recommended knowledge

The origins of HAZOP Studies are in the British chemical industry and its adoption was driven by the 1974 Flixborough explosion, where lack of a systematic review of modifications by appropriately qualified personnel was identified as a contributing factor.


The methodology may be applied to any process or project although most practitioners and expertise originate in the chemical and offshore industries. A HAZOP uses guide words (e.g. "more", "less", "as well as") and parameters (e.g. "temperature", "control", "ventilation") to consider process intent, possible deviations from the intended process, the consequences of any deviations, and the hazards presented by these consequences.[1][2][3] The following table gives an overview of commonly used guide word - parameter pairs and common interpretations of them.

Parameter / Guide Word More Less None Reverse As well as Partly Other than
Flow high flow low flow no flow reverse flow deviating concentration contamination deviating material
Pressure high pressure low pressure vacuum delta-p explosion
Temperature high temperature low temperature
Level high level low level no level different level
Time too long / too late too short / too soon sequence step skipped backwards missing actions extra actions wrong time
Agitation fast mixing slow mixing no mixing
Reaction fast reaction / runaway slow reaction no reaction unwanted reaction
Start-up / Shut-down too fast too slow actions missed wrong recipe
Draining / Venting too long too short none deviating pressure wrong timing
Inertising high pressure low pressure none contamination wrong material
Utility failure (instrument air, power) failure
DCS failure failure
Maintenance none
Vibrations too low too high none wrong frequency

Once the causes and effects of any potential hazards have been established, the system being studied can then be modified to improve its safety.

See also


  1. ^ Center for Chemical Process Safety (1992). Guidelines for Hazard Evaluation Procedures, with Worked Examples, 2nd Edition, Wiley-AIChE. ISBN 0-8169-0491-X. 
  2. ^ Vesely, W.E., Goldberg, F.F., Roberts, N.H. and Haasl, D.F. (1981). Fault Tree Handbook. U.S. Nuclear Regulatory Commission. NUREG-0492.  Nuclear Regulatory Commission (Pdf file)
  3. ^ Kletz, Trevor (1999). Hazop and Hazan, 4th Edition, Taylor & Francis. ISBN 0-85295-421-2. 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Hazop". A list of authors is available in Wikipedia.
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