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Volume 14, Number 1           A Gossman Consulting, Inc. Publication       March 2009

HAZOP - Pros and Cons


David Gossman

In 1998 we published a GCI Tech Notes that summarized the HAZOP process.  Recently I had the opportunity to teach a class on performing HAZOPs to a group of safety professionals in Shanghai, China.  As a result of that experience further information on the process of performing HAZOPs will be presented in a new series of GCI Tech Notes starting with this issue.


A Hazard and Operability (HAZOP) study is a structured and systematic examination of a planned or existing process or operation in order to identify and evaluate problems that may represent risks to personnel or equipment, or prevent efficient operation.  The HAZOP technique was initially developed to analyze chemical process systems, but has later been extended to other types of complex systems including, as examples, transportation systems and software systems.  The  HAZOP process is just one of a large number of different techniques available to the safety professional for analyzing systems to identify and prevent hazards. It has the further advantage that it also identifies and helps to prevent operational problems.  HAZOP studies require more details regarding the systems under consideration, but produce more comprehensive information on hazards and errors in the system design.  As with any of these processes there are pros and cons to using a specific technique for a particular circumstance.  HAZOPs are not the best technique for every circumstance and it is important to understand the benefits as well as the costs and limitations of the method before making the decision to use it in a particular circumstance.


HAZOP is a hazard identification technique which considers system parts separately and systematically examines the effects of deviations on each part. Sometimes a serious hazard will involve the interaction between a number of parts of the system. In these cases the hazard may need to be studied in more detail using techniques such as event tree and fault tree analyses.  Many systems are highly inter-linked, and a deviation at one of them may have a cause elsewhere. Adequate local mitigating action may not address the real cause and still result in a subsequent accident.  Many accidents have occurred because small local modifications had unforeseen knock-on effects elsewhere. While this problem can be overcome by carrying forward the implications of deviations from one part to another, in practice this is frequently not done.  As with any technique for the identification of hazards or operability problems, there can be no guarantee that all hazards or operability problems will be identified in a HAZOP study. The study of a complex system should not, therefore, depend entirely upon a HAZOP. It should be used as a compliment to other suitable techniques. It is essential that other relevant studies are coordinated within an effective overall safety management system.  The success of a HAZOP study depends greatly on the ability and experience of the study leader and the knowledge, experience and interaction between team members.  HAZOP only considers parts that appear on the design representation. Activities and operations which do not appear on the representation are not considered.


An important benefit of HAZOP studies is that the resulting knowledge, obtained by identifying potential hazards and operability problems in a structured and systematic manner, is of great assistance in determining appropriate remedial measures.  While a HAZOP is not appropriate in all circumstances one of the major benefits that can be used to help justify the cost and time investment is that it also helps to avoid operating problems and can thus provide a clear return on the investment beyond the reduction in hazards.