Guide Words for HAZOP Studies

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 ... 

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. 

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 ... 

The HAZOP team examines each study node for potentially hazardous process deviations. First, the design intent is defined to delineate the purpose of the equipment and the process parameters. Process deviations are determined by combining guide words with the important process parameters. The established set of guide words is shown in Table 4.14. 

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 Analysis (Hazop) (Kletz, 1992) is one of the most used safety analysis methods in the process industry. It is one of the simplest approaches to hazard identification. Hazop involves a vessel to vessel and a pipe to pipe review of a plant. For each vessel and pipe the possible disturbances and their potential consequences are identified. Hazop is based on guide words such as no, more, less, reverse, other than, which should be asked for every pipe and vessel (Table 1). The intention of the quide words is to stimulate the imagination, and the method relies very much on the expertise of the persons performing the analysis. The idea behind the questions is that any disturbance in a chemical plant can be described in terms of physical state variables. Hazop can be used in different stages of process design but in restricted mode. A complete Hazop study requires final process plannings with flow sheets and PID s. 

The approach to identifying hazards and operability problems by this technique is to search for deviations from design intents. The first step is to plan the HAZOP study to ensure that there is sufficient time, expertise, and information available. Next, a multidisciplinary team, led by an expert in the technique, is set up. Then, by means of a fixed set of abstract words called guide words (such as more ), the team leader examines each process... 

The results of the HAZOP study are summarised in Table 9.8, where guide-words which do not proceed nor provide additional insights for this specific case have already been omitted. 

Table 9.9 HAZOP study for the system of Fig. 9.5 (guide words which do not proceed were left out after examination)...

Use guide words such as no/less/excess/more/higher, etc., for various parameters such as flow of reactants, heating medium, cooling water, and levels in tanks for each section of the plant to examine further (more details are given below for such HAZOP study). 

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). 

Therefore recording and report preparation can never be overestimated. It is worth noting that all the background information based on which study has been carried out should be part of the dossier. This will be helpful for further reference as well as to mark the changes in the future. Therefore the amount of information in the HAZOP final report will vary from case to case. Each section shall be covered fully with a selection of guided words and a heading. 

HAZOP study for procedure This is normally a detailed method and should be properly defined. This study is usually carried out by a well-balanced team from different disciplines. The information required includes but is not limited to procedure definitions, up-to-date P IDs, and other relevant drawings and documents. Also the aim of the study (depth of study and major area of interest such as HSE, accident, etc.) needs to be well defined before starting a step-by-step procedure. Each stage/step and action is examined with the guide word to identify meaningful deviation for analysis for hazard identification. In the case of a HAZOP study for procedure, human error is an important factor. 

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