HAZOP parameters, deviations, and possible

Appendix E HAZOP Parameters, Deviations, and Possible Causes... 

The following are typical guideword parameter, deviations, and possible causes that are used in HAZOP reviews. This listing is by no means exhaustive and each review should be supplemented or tailored to meet the needs of a particular facility. 

Sometimes referred to as energy flow analysis, HazOps is used primarily in the petrochemical industry. It uses a multidisciplinary team similar to a system safety working group for the systematic review of the flow of materials through a process. It concentrates on key locations in the process known as study nodes and uses a series of guide words and parameters to examine possible deviations and the causes and consequences of deviations (Goidwaite 1985). 

Table 10-6 presents one type of basic HAZOP form. The first column, denoted Item, is used to provide a unique identifier for each case considered. The numbering system used is a number-letter combination. Thus the designation 1 A would designate the first study node and the first guide word. The second column lists the study node considered. The third column lists the process parameter, and the fourth column lists the deviations or guide words. The next three columns are the most important results of the analysis. The first column lists the possible... 

Hazard and Operability study (HazOp) A technique for identifying hazards and operating problems by using a series of guide words to identify possible deviations from intended process parameters. 

Although not mandatory in the HAZOP method, this study comprised a risk assessment to all deviations detected. Risk assessment was performed through the use of a risk matrix already used in similar industries which included the combination of probability (possibility that the event occurs) and severity (as a consequence of the event). For the risk assessment criteria, four levels of probability were defined very unlikely/remote, likely/possible, probable and frequent. For severity were defined also four levels reduced, moderate, high, very high/catastrophic. The designation of risk parameters took into account the probability of occurrence, the measures implemented, historical events, potential injury to persons, to materials, to the environment. The combination between the four levels lead to four types of risk, grouped in two levels, acceptable/not significant, which even... 

The HAZOP study was originally developed for the chemical process industry. The analysis team applies a set of so-called guidewords (like OTHER THAN or MORE ) to each combination of a process step (for instance a vessel) with a parameter (e.g. temperature) and analyses possible deviations fi-om design or process intent expressed by the combinations with respect to causes, consequences, and existing detection as well as risk mitigation measures finally, further risk reduction measures are recommended if necessary. 

Here is a table based on the HAZOP guide published by UK I Chem. E for typical derived guidewords generated by the parameter and guideword combinations for some process parameters. This table makes it easier to visualize the possible deviations. 

The HAZOP team focuses on specific portions of the process called nodes . A process parameter (e.g. flow) is identified and an intention is creat for the node under consideration. Then a series of guidewords is combined with the parameter flow to create a deviation. For example, the guideword no is combined with the parameter flow to give the deviation no flow . The team then focuses on listing all the credible causes of a no flow deviation beginning with the cause that can result in the worst possible consequences the team can think of at the time. Once the causes are recorded, the team lists the consequences, safeguards and any recommendations deemed appropriate. The process is repeated for the next deviation until completion of the node. The team moves on to the next node and repeats the process. 

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