Hazard and Operability Study Technique (HAZOP)

Safety concerns in the oil and chemical process industries are mainly associated with the operation of the plant, the reliability of equipment and design of the process. The hazard and operability study was developed for use in the chemical and petroleum industries. It is based on the theory that most hazards are missed because the system is complex, rather than a lack of knowledge during design. Operability studies identify hazardous or unacceptable situations, according to Knowlton (1985).

Hazard analysis provides a quantitative examination of a serious hazard that has been identified, either by an operability study or by some other hazard identification method. It quantifies the effect of hazards as well as unacceptable situations.

During hazard and operability studies the two methods are brought together, according to the hazard and operability studies training manual published by International Risk Control Africa under licence of Det Norske Veritas of Sweden.

During a hazard and operability study the plant being examined are evaluated line-by-line and vessel-by-vessel. The HAZOP study system results from two techniques used to examine the risks as follows:

The first part of the study that focuses on the operability is based on a method developed by ICI. This operability assessment system is widely utilized by chemical and petroleum companies. The concept is founded on the conviction that most health and safety problems in a chemical conversion system or petroleum plant are disregarded as a result of the complexity of the system. It was found that the design team more often than not does not have a lack of knowledge of the system and the risk associated with the system.

The operability concept is principally used to examine the process design flow sheets at the start of a project as a preliminary step. It is also ideal to use this approach to scrutinize the detailed designs and layouts such as the instrument and piping configurations when the final design stage is reached. In some plants the approach is also successful utilized during full operation of the plant.

The second component of the technique, the hazard analysis part, is designed to provide a systematic methodology to achieve a quantitative outcome to the examination. This component utilizes the outcome of the operability phase to assess any serious hazard that has been identified to assess.

The process is based on a cause consequence logic fault tree that relates the events capable of leading to a specific hazard. The nodes in the tree are systematically quantified to produce the probability of the identified hazard so that it can be more easily understood and interpreted. The event consequences are quantified systematically with the aid of a mathematical modelling technique.

The procedure utilized in a HAZOP study is basically the creation of questions, by a knowledgably team, who ensures that complete and systematic coverage of all the applicable areas in the process is covered. The assessment team consists of design and operations personnel with sufficient technical experience and expert knowledge of the particular process and design to ensure full coverage.

The focus of the questions is to detect any design defect or process variation that may be present that could lead to safety or operability problems.

To summarise, the Operability Study identifies hazardous or unacceptable situations and Hazard Analysis quantifies the effects. The term HAZOP brings together the methods used by both.

© 2009 Carl Marx