Guide words

Table 1. List of Guide Words for HAZOP Procedure ...

Item Study node Process parameters Deviations (Guide words) Possible causes Possible consequences Action required Assigned to i i... 

Guide words—simple words used to qualify the intention in order to guide and stimulate creative thinking and so discover deviations. Table 26-2 describes commonly used guide words. 

Deviations—departures from the intention discovered by systematic application of guide words. 

The guide words can be used on broadly based intentions (see Table 26-2), but when intentions are expressed in fine detail, some restrictions or modifications are necessary for chemical processes, such as ... 

This gives a process plant a specific HAZOP guide-word list with a process variable, plant condition, or an issue. 

TABLE 26-2 Some Guide Words Used in Conjunction with Process Parameters... 

TABLE 26-3 Guide Words Associated with Time... 

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. 

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. 

The procedure for a HAZOP study is to apply a numher of guide words to various sections of the process design intention. The design intention informs what the process is expected to caiTy out. Table 12-6 shows these guide words, and Figure 12-42 summarizes the entire procedure. Common property words are ... 

List of guide words used for the HAZOP procedure... 

Part of Design intentions only partly achieved. It IS more precise to use the guide word less" wherever possible. However, fluctuations m a property word are covered by part of. 

System (node) Selection Design Intent Guide Words Cause Identification Consequence Identificatidn Resolution Review Record... 

A guide word (or phrase) is a perturbation on a process variable, component or system. 

I iach study node is examined for potentially hazardous process deviations. First, i he design inte-iit of the equipment and the process parameters is determined and recorded. Process de iatiuns from the design are determined by associating guide words with important process parameters. (iiiidt words for a HAZOP analysis are shown in Table 3.3.4--1 process parameters and dt. i itions are shown in 1 able, T3.4-2. 

By combining elements of the first column of the guide words with elements of columas 2 or 4 of the process parameters, process deviations may be found. For example, combining the first guide word, "No" from Table 3.3.4-1 with the first process parameter, Flow rate from Table >.3 4-4, the deviation No flow rate" is found. Other deviations may be created similarly... 

Several systems (nodes) at a time may be in the process of review and resolution. In some casc.s, ilic causes and consequences for a given section, system, node, and guide word can be readily... 

A pipeline for this purpose is one joining two main plant items—for example, we might start with the line leading from the feed tank through the feed pump to the first feed heater. A series of guide words are applied to this line in turn, the words being ... 

The same questions are then applied to reverse flow, and we then move on to the next guide word, MORE OF. Could there be more flow than design If so, how could it arise And so on. The same questions are asked about more pressure and more temperature, and, if they are important, about other parameters, such as more radioactivity or more viscosity. ... 

When studying a batch plant, the guide words should be applied to the instructions as well as the pipelines. For example, if an instruction says that I ton of A should be charged to a reactor, the hazop team should consider the effects of the following deviations ... 

Another danger of an inadequate appreciation of human causes of hazards is that the HAZOP analyst may consider a particular high risk event (identified by a guide word and deviation) to be noncredible, because he or she only takes into accoimt the hardware failures (with an extremely low probability) that could give rise to the event. When human causes are taken into accoimt, the likelihood of the event may actually be quite high. 

GUIDE WORD DEVIATION CONSEQUENCES CAUSES SUGGESTED ACTION... 

TABLE 14.3.1 Guide Words Used to Relay the Degree of Deviation from Intended SubprocessOperation... 

TABLE 15.7.1 Guide Words Used in HAZOP Studies... 

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