Hazard and Operational Study (HAZOP)

A HAZOP study identifies hazards and operability problems. The concept involves investigating how the plant might deviate from the design intent. If, in the process of identifying problems during a HAZOP study, a solution becomes apparent, it is recorded as
part of the HAZOP result; however, care must be taken to avoid trying to find solutions which are not so apparent, because the prime objective for the HAZOP is problem identification. HAZOP is based on the principle that several experts with different backgrounds can interact and identify more problems when working together than when working separately and combining their results.
The process is systematic and it is helpful to define the terms that are used:

The Concept
The HAZOP concept is to review the plant in a series of meetings, during which a multidisciplinary team methodically ―brainstorms‖ the plant design, following the structure provided by the guide words and the team leader’s experience. The team focuses on specific points of the design (called “study nodes”), one at a time. At each of these study nodes, deviations in the process parameters are examined using the guide words. The guide words are used to ensure that the design is explored in every conceivable way. Thus the team must identify a fairly large number of deviations, each of which must then be considered so that their potential causes and consequences can be identified. The best time to conduct a HAZOP is when the design is fairly firm. There is a natural relationship between the HAZOP deviation approach and the usual control system design philosophy of driving deviations to zero; thus it is very effective to examine a plant as soon as the control system redesign is firm.

The success or failure of the HAZOP depends on several factors:

  • The completeness and accuracy of drawings and other data used as a basis for the study
  • The technical skills and insights of the team
  • The ability of the team to use the approach as an aid to their imagination in visualizing deviations, causes, and consequences
  • The ability of the team to concentrate on the more serious hazards which are identified.

Steps in conducting a HAZOP
Define the purpose, objectives, and scope of the study
Select the team
Prepare for the study
Carry out the team review
Record the results.

It is important to recognize that some of these steps can take place at the same time. For example, the team reviews the design, records the findings, and follows up on the findings continuously. Each step is discussed below as a separate item.

Define the Purpose, Objectives, and Scope of the Study
The purpose, objectives, and scope of the study should be made as explicit as possible. These objectives are normally set by the person responsible for the plant or project, assisted by the HAZOP study leader (perhaps the plant or corporate safety officer). It is important that this interaction take place to provide the proper authority to the study and to ensure that the study is focused. Also, even though the general objective is to identify hazards and operability problems, the team should focus on the underlying purpose or reason for the study. Examples of reasons for a study might be to:

Check the safety of a design
Decide whether and where to build
Develop a list of questions to ask a supplier
Check operating/safety procedures
Improve the safety of an existing facility
Verify that safety instrumentation is reacting to best parameters.

It is also important to define what specific consequences are to be considered:
Employee safety (in plant or neighboring research center)
Loss of plant or equipment
Loss of production (lose competitive edge in market)
Public safety
Environmental impacts.

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