1.1.1.1.

Hazard and Operability (HAZOP) studies methodology was developed by ICI in the United Kingdom during the early 1960s as it required a more formalised technique for critical analysis of plant design and operation. They had reviewed the techniques being used in various parts of the company, and concluded that their quality was too heavily dependent on the people who made up the study teams. They asked the Method Study experts in the company to devise a formal review technique, and to hand it over to the engineers for use in new plant reviews. The basic HAZOP methodology was then devised by the team to fulfil these requirements.

1.1.1.3.

The HAZOP procedure involves a multi-disciplinary team who has substantial experience of the system or design to be studied. The team consider taking a full description of a process and systematically question every part of it to establish how deviations from the design intent can arise. For each credible deviation the group considers possible causes and consequences and decides if additional safeguards should be recommended when consequences are found to have a negative effect upon the safe and efficient operation of the plant. This examination of the design is structured around a specific set of guidewords, which ensure complete coverage of all possible problems whilst allowing sufficient flexibility for an imaginative approach.

1.1.1.5.

The HAZOP technique is very versatile, and can be applied to both continuous and batch processing. Generally, the HAZOP methodology is intended for use on a continuously operating system, although in concept it is equally applicable to a batch process. In fact, if one considers the start-up and shutdown procedures of a continuous process plant, it can be shown that it is nothing more than a batch plant with a long reaction cycle. However, there are several important differences in the HAZOP procedure, such as, data required, preparation time, and study time that must be understood in order to plan and carry out such a study. These differences apply when the complete process unit is operated batchwise and also when there is only a single batch process step in a large continuous unit.

1.1.1.7.

If a batch process is converted to continuous, it will almost always result in a system with more main plant items. It is, therefore, almost always true that the study time required will be significantly greater for a batch system than for a similar Process and Instrumentation Diagram of a continuous process.

1.1.2.1.

As mentioned, HAZOP is primarily used for identifying safety hazards and operability problems of continuous process systems and for the review of procedures and sequential operations. Overall, HAZOP has become a standard tool across a variety of sectors (e.g. petrochemical, offshore) and procedural HAZOP is widely used for both simultaneous operations and the assessment of evacuation systems. However, other HAZID techniques may be more efficient for many marine hazards depending upon the experience and availability of the team, the phase of the design, the information available, etc.

1.1.3.1.

Advantages

• It is widely-used and its advantages and disadvantages are well understood and well known
• It uses the experience of operating personnel as part of the team
• It is systematic and comprehensive, and should identify all hazardous deviations from the design intent and also from the operability perspective
• It is effective for both technical faults and human errors. It recognises existing safeguards and develops recommendations for additional ones
• The team approach is particularly appropriate to requiring the interaction of several disciplines or organisations
• It provides a means of assessing hazards before a system becomes operational
• The method aids the derivation of corrective and preventive measures that may be incorporated into the system.

1.1.6.1.

Fuel oil is transferred from a tanker to a ship as shown in Figure 1. A simple sketch describing part of the system is shown in Figure 2. In this example we shall apply the HAZOP technique to the equipment shown. We are interested in safety hazards and environmental aspects.

1.1.6.3.

The fuel is at ambient temperature; the pressure is negative static head at the pump suction and 3 barg maximum at pump discharge. The storage tanks are at atmospheric pressure with capacities of 50 and 20 m3 respectively for the tanker and receiving ship. Fuel flow rate is 500 litres per minute. It is assumed that level measurement in the tanks is by manual dipping and that the pump is started and stopped using a local pushbutton. A procedure is in place for correct configuration of the pipework and equipment and subsequent transfer of the fuel.

1.1.6.5.