HAZOP study

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. 

Some studies have shown that a HAZOP study will result in recommendations that are 40 percent safety-related and 60 percent operability-related. HAZOP is far more than a safety tool a good HAZOP study also results in improved operability of the process or plant, which can mean greater profitability. 

The primaiy goal in performing a HAZOP study is to identify, not analyze or quantify, the hazards in a process. The end product of a study is a hst of concerns and recommendations for prevention of the problem, not an analysis of the occurrence, frequency, overall effects, and the definite solution. If HAZOP is started too late in a project, it can lose effectiveness because ... 

Control actions, e.g., provide alarms to indicate things getting out of control define control actions to get back into control. The HAZOP study is not complete until response to actions has been documented. Initial HAZOP planning should establish the management follow-up procedure that will be used. 

HAZOP studies involve a team, at least some of whom have had experience in the plant design to be studied. These team members apply their expertise to achieve the aims of HAZOP. There are four overall aims to which any HAZOP study should be addressed ... 

Computer tools are available to aid information capture. In some cases, tbe facilitator may use tbe computer tool for recording, replacing tbe secretaiy. For example, PrimaTecb offers a veiy useful computer program to aid in HAZOP studies (HAZOP-PC, 1994). Other excellent computer aids for HAZOP are also commercially available. 

When considering release scenarios, the most hazardous unit in a plant should be chosen, based on inventoiy and process conditions. The idea is to imagine the release of material in the fastest way that is reasonably possible. The worst realistic scenario should be considered. This can be based on the outcome of a review, from a HAZOP study or a hazard analysis. The time a scenario will take is almost always considered to be continuous, because after a few minutes a stable dispersion distance exists. Making the time longer will not necessarily change the hazard distance. 

Two members selected from the team act in supportive roles during the PHA. These roles are the leader and the scribe. A team leader is always needed for a PHA and should double as the scribe only for extremely simple hazard evaluations. For more complex analyses or the HAZOP study method, a separate person should always be assigned to scribe. 

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. 

A HAZOP study is a structured review of the plant design and operating procedures. The main goals are to ... 

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 ... 

The HAZOP study proceeds in a systematic mamier that reduces the possibility of omi ssion. Within a study node, all deviations associated with a given process parameter should be analyzed before the ne.xt proces.s parameter is considered. All deviations for a study node should be analy zed before the team proceeds to the next node. 

A HAZOP study is a systematic, tabular document of process deviations. The study gives the noimal operating conditions and analysis boundary conditions for each item and lists action items for further evaluation. Tables 3.34-3 and 3.3.4-4 are examples of HAZOP analysis of the Dock 8 HF Supply System and the Cooling Tower Chlorination System, respectively (for a more complete study see DOE, 1973). These example show the format for HAZOP tables. A typical HAZOP study... 

Staff requirements for a HAZOP depend on the size and complexity of the process being analyzed. Time and cost are proportional to the size of the process and the experience of the study leader and team members. Table 3.3.4-5 presents estimates of the time needed to perform a PrHA using the HAZOP study method (CCPS, 1992). Study sessions should be limited to 3 consecutive... 

The primary limitation of a HAZOP study is the length of time required to perform it. Because the study is designed to provide a complete analysis, study sessions can be intensive and lii ing. HAZOP studies typically do not look at occupational hazards (e.g., electrical equipment, rotating equipment, hot surfaces) or chronic hazards (e.g., chronic chemical exposure, noise, heat stress). For experience with HAZOP see Swann (1995). 

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... 

What if Approaches Hazind and Operability (HAZOP) Studies Preliminary Hazard Analysis (PLHA) Process Hazard Analysis (PHA)... 

A HAZOP study may be applied to operating process plants, or it may be performed at various stages Unoughout the design. An early start will lead to a safer, more efficient design and, ultimately, liigher profits. 

Before any action is taken, die goals of the study should be defined. There are six objectives to a HAZOP study ... 

A reladvely simple example of a HAZOP study using guidewords is shown for a boiler drum in Fig. 15.7.1 and Table 15.7.2. The intent of die operation is to maintain die water level in die horizontal drum between 30 and 40% of die volume. 

TABLE 15.7.1 Guide Words Used in HAZOP Studies... 

List and discuss the seven key guide words that are employed in a HAZOP study. 

Tliis particular case study does illustrate how event tree and fault tree analysis can be used in a hazard operability (HAZOP) study. 

The term operability study should more properly be used for this type of study, though it is usually referred to as a hazard and operability study, or HAZOP study. This can cause confusion with the term hazard analysis , which is a technique for the quantitative assessment of a hazard, after it has been identified by an operability study, or similar technique. Numerous books have been written illustrating the use of HAZOP. Those by Hyatt (2003), AIChemE (2000), Taylor (2000) and Kletz (1999a) give comprehensive descriptions of the technique, with examples. 

Devise a preliminary control scheme for the sections of the nitric acid plant described in Chapter 4, flow-sheet Figure 4.2, which are listed below. Make a practice HAZOP study of each section and revise your preliminary control scheme. 

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