Hazard and operability

Plant components (pumps, compressors, exchangers) are found within nodes. In the same fashion, a parameter is an aspect of the process that describes it physically, chemically, or in terms of what is happening (flow, level, temperature). Parameters are usually classified as specific or general to respectively describe aspects of the 

Note significant consequences for each cause Note existing safeguards Document recommendations, if any Assign responsibility for recommendation 

The HAZOP procedure is a powerful tool for hazard analysis and its methodical approach ensures that weaknesses in the design intent are detected and acted upon. HAZOP is widely used in RBI processes. It is also applied at an early design stage through corrosion-risk assessments as a documented process for materials selection and corrosion prevention. The strengths of HAZOP are [10] 

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Here we shall restrict consideration to safety and health considerations that can be built in while the design is developing rather than the detailed hazard and operability studies that take place in the later stages of design. The three major hazards in process plants are fire, explosion, and toxic release. ... 

As the design progresses, it is necessary to carry out hazard and operability studies. These are generally only meaningful when the design has been progressed as far as the preparation of detailed flowsheets and are outside the scope of this text. 

Design procedures are developed with the intention of improving the safety of equipment. Tools used in this step are hazard and operability studies and quantitative risk analysis (ORA). The following scheme may be used ... 

Hazard and Operability Analysis. The hazard and operabihty analysis (HAZOP) procedure is quite popular because of its ease of use, the abihty to organize and stmcture the information, minimal dependence on the experience of the analysts, and the high level of results. Furthermore, the approach is capable of finding hazards associated with the operation of a faciUty, hence the incorporation of the word operabihty in the name. 

Control of Plant and Process Modifications Many accidents have occurred because plant or process modifications had unforeseen and unsafe side effects (Sanders, Management of Change in Chemical Plants Learning from Ca.se Histories, Butterworth-Heinemann, 1993). No such modifications shoiild therefore be made until they have been authorized by a professionally quahfied person who has made a systematic attempt to identify and assess the consequences of the proposal, by hazard and operability study or a similar technique. When the modification is complete, the person who authorized it... 

HAZOP (Knowlton, 1989 Lees, 1980 CPQRA, 1989, pp. 419-422). HAZOP stands for hazard and operability studies. This is a set of formal hazard identification and elimination procedures designed to identify hazards to people, process plants, and the environment. The techniques aim to stimulate in a systematic way the imagination of designers and people who operate plants or eqmpment so they can identify potenti hazards. In effect, HAZOP studies make the assumption that a hazard or operating problem can arise when there is a deviation from the design or operating intention. Corrective actions can then be made before a real accident occurs. 

Hazard and Operability Study (HAZOP) A systematic qualitative technique to identify process hazards and potential operating problems using a series of guide words to study process deviations. 

The cost of performing the hazard identification step depends on the size of the problem and the specific techniques used. Techniques such as brainstorming, what-if analyses, or checklists tend to be less expensive than other more structured methods. Hazard and operability (HAZOP) analyses and failure modes and effects analyses (FMEAs) involve many people and tend to be more expensive. But, you can have greater confidence in the exhaustiveness of HAZOP and FMEA techniques—their rigorous approach helps ensure completeness. However, no technique can guarantee that all hazards or potential accidents have been identified. Figure 8 is an example of the hazards identified in a HAZOP study. Hazard identification can require from 10% to 25% of the total effort in a QRA study. 

R. E. Knowlton, Hazard and Operability Studies, The Guide Word Approach, Chemetics International Company, Vancouver, BC, 1981. 

A HAZOP (Hazard and Operability Study) involves a fonual review of proeess and instrumentation diagrams by a speeialist team using a stmetured teehnique, based upon key words. These eomprise property words and guide words , e.g. as in Table 12.4. 

Hazard and operability study prior to implementation (repeat when in use) Updating of all operating instructions, notices, procedures Removal/isolation of obsolete plant/lines Control of changes in personnel (see training)... 

Refresher course on fundamentals of safety, hazard recognition, procedures Participation in hazard and operability studies on existing operations and procedures... 

The design and operation of a proeess plant form an integral part of safety and systematie proeedures and should be employed to identify hazards and operability and, where neeessary, should be quantified. During die design of a new plant, die hazard identifieation proeedure is repeated at intervals. This is first performed on the pilot plant before the full-seale version as the design progresses. Potential hazards whose signifieanee ean be assessed with the help of experiments are often revealed by this study. 

Many accidents occur because process materials flow in the wrong direction. Eor example, ethylene oxide and ammonia were reacted to make ethanolamine. Some ammonia flowed from the reactor in the opposite direction, along the ethylene oxide transfer line into the ethylene oxide tank, past several non-return valves and a positive displacement pump. It got past the pump through the relief valve, which discharged into the pump suction line. The ammonia reacted with 30m of ethylene oxide in the tank, which ruptured violently. The released ethylene oxide vapor exploded causing damage and destruction over a wide area [5]. A hazard and operability study might have disclosed the fact that reverse flow could occur. 

We put a lot of effort into improving safety by adding protective equipment onto our plants, new and old gas detectors, emergency isolation valves, interlocks, steam curtains, fire insulation, catchment pits for LPG storage tanks, and so on. We also introduced new procedures, such as hazard and operability studies and modification control, or persuaded people to follow old ones, such as permits-to-work and audits. 

FIAZOP is a formally struetured method of systematieally investigating eaeh element of a system for all ways where important parameters ean deviate from the intended design eonditions to ereate hazards and operability problems. The HAZOP problems are typieally determined by a study of the piping and instrument diagrams (or plant model) by a team of personnel who eritieally analyze eflfeets of potential problems arising in eaeh pipeline and eaeh vessel of the operation. 

A more speeifie example is the use of a PHA eheeklist for a standard boiler or heat exehanger and the use of a Hazard and Operability PHA for the overall proeess. Also, for bateh-type proeesses like eustom bateh operations, a generie PHA of a representative bateh may be used where there are only small ehanges of monomer or other ingredient ratio and the ehemistry is doeumented for the full range and ratio of bateh ingredients. 

Hazards and Operability (HAZOP) analysis is an accident detection and prevention technique used primarily by the chemical process industry (CPI) (Lees, 1980). Even though the CPI operates in a different regulatory environment from the commercial nuclear power industry, the goals of risk reduction while maintaining productivity are similar. 

Hazards and Operability (HAZOP) Facility Risk Review Quantitative Risk Analysis... 

The most common predictive technique which is used to analyze facilities which contain new equipment or processes, or where there is an unusually high risk to personnel or the environment is the Hazard and Operability technique or HAZOP. A HAZOP study requires a team of five to ten multi-discipline personnel consisting of representatives from engineering, operations, and health, safety, and environmental staff. The... 

This incident shows the importance, during hazard and operability studies (see Chapter 18), of considering abnormal conditions, such as failure of utilities, as well as normal operation. 

Should the design team have foreseen that the condensate might freeze A hazard and operability study (see Chapter 18) would probably have drawn attention to the hazard. 

The managers and engineers who authorize modifications cannot be expected to stare at a drawing and hope that the consequences will show up. They must be provided with an aid, such as a list of questions to be answ ered. Such an aid is shown in References 1 and 2. Large or complex modifications should be subjected to a hazard and operability study (see Chapter 18). 

This chapter is not concerned with accidents on the road. Rather, it describes some of the many incidents that have occurred while tank trucks and cars (known in Europe as road and rail tankers) were being filled or emptied. Section 18.8 shows how hazard and operability studies have been used to spot potential hazards in filling systems, and Section 22.3 describes some runaway reactions in tank trucks and cars.. 

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