Hazard identification, HAZOP

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. 

Most hazard identification procedures have the capabiUty of providing information related to the scenario. This includes the safety review, what-if analysis, hazard and operabiUty studies (HAZOP), failure modes and effects analysis (FMEA), and fault tree analysis. Using these procedures is the best approach to identifying these scenarios. 

Fire and Explosion Index (Ffrom fires and explosions. frequency The rate at which observed or predicted events occur. HAZOP HAZOP stands for hazard and operabihty studies. This is a set of formal hazard identification and ehmination procedures designed to identify hazards to people, process plants, and the environment. See subsequent sections for a more complete description. 

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. 

The What if..method, the checklist, and HAZOP are well-publicized hazard identification tools. CCPS (1992) presents guidance on the use of these tools. 

Hazard Identification, the main sources of ammonia that could release are identified and the initiating events (IE) that can cause accidents leading to the release of ammonia are determined. Three methods used for IE identification were Master Logic Diagram, checklists, and HAZOP... 

An opportimity for error recovery would have been to implement a checking stage by a supervisor or independent worker, since this was a critical maintenance operation. However, this had not been done. Another aspect of the unforgiving environment was the vulnerability of the system to a single human error. The fact that the critical water jacket flow was dependent upon a single pump was a poor design that would have been detected if a hazard identification technique such as a hazard and operability study (HAZOP) had been used to assess the design. 

All of these factors determine the stress experienced by the workers and the extent to which operational errors will be recovered before disastrous consequences have ensued. In this context, hazard identification techniques, such as hazard and operability studies (HAZOP), failure modes and effects and criticality analysis (FMECA), fault trees, and others are useful in making the process environment more forgiving. 

Hyatt, N. (2003) Guidelines for Process Hazard Analysis (PHA. Hazop), Hazard Identification and Risk Analysis (CRC Press). 

The hazards identification procedures presented in chapter 10 include some aspects of risk assessment. The Dow F EI includes a calculation of the maximum probable property damage (MPPD) and the maximum probable days outage (MPDO). This is a form of consequences analysis. However, these numbers are obtained by some rather simple calculations involving published correlations. Hazard and operability (HAZOP) studies provide information on how a particular accident occurs. This is a form of incident identification. No probabilities or numbers are used with the typical HAZOP study, although the experience of the review committee is used to decide on an appropriate course of action. 

A number of hazard identification and analysis techniques (e.g., HAZOP), can be applied to identify, analyze, and reduce and/or mitigate the process hazards, which includes handling of reactive chemicals and energetic reactions. Chapter 4 provides an overview of these kinds of techniques as related to reactive chemicals mote detailed reviews of hazards analysis techniques are included in [2,3]. 

The What-if, the checklists and Hazop are well publicized hazard identification tools. But as Bollinger et al. (1996) have pointed out the use of any of these techniques demands knowledge, experience and flexibility. No prescriptive set of questions or key words or list is sufficient to cover all processes, hazards and all impacted populations. Bollinger et al. find that refinement of the quantitative measurement techniques such as safety indices and convergence to a single set of accepted indices would be beneficial. 

Also indices such as the Dow Fire and Explosion Hazard Index and the Mond Index have been suggested to measure the degree of inherent SHE of a process. Rushton et al. (1994) pointed out that these indices can be used for the assessment of existing plants or at the detailed design stages. They require detailed plant specifications such as the plot plan, equipment sizes, material inventories and flows. Checklists, interaction matrices, Hazop and other hazard identification tools are also usable for the evaluation, because all hazards must be identified and their potential consequences must be understood. E.g. Hazop can be used in different stages of process design but in restricted mode. A complete Hazop-study requires final process plans with flow sheets and PIDs. 

Failure mode and effect analysis (FMEA) A hazard identification technique in which all known failure modes of components or features of a system are considered in turn and undesired outcomes are noted. It is often used in combination with hazard and operability (HAZOP) studies or fault tree analysis. 

HAZOP (HAZard and OPerabdity study) A formal hazard identification and evaluation procedure based on the application of guide words to identify possible deviations from the intended operation of the process. 

HAZOP (HEP, 1992, Chaps. 4.7, 6.7, 14, 18 Knowlton, 1989 Lees, 2005 CPQRA, 2000, pp. 583 587). HAZOP is a formal hazard identification and evaluation procedure 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... 

See also Hazard acceptance Hazard assessment Hazard identification entries limitations of, 13 153-154 probability, 13 166-170 purpose of, 13 152 scenario identification, 13 165 source modeling and consequence modeling, 13 165-166 sustainable development and, 24 183-188 techniques for, 13 152-154 Hazard and operability (HAZOP) analysis, 13 154, 157-159 guide words for, 13 158t sample, 13 159... 

The hazard identification methods presented in Sections 1.5.1 to 1.5.6 above are all based on strongly systematic procedures. In the check list method, the systematic is provided by the check list itself. The comprehensiveness can be verified in the matrix (see Figures 1.4 and 1.5). With the FMEA, the systematic is provided by the division of the system into elements and the failure modes considered. In the HAZOP study, the systematic stems from the division of the plant into nodes and lines, then the systematic application of the keywords. With the decision table method, the systematic is inherent to the table. For the FTA and ETA, the systematic is given by the tree and the logical ports. Nevertheless, the work of the team must be traceable, even by persons who did not participate to the analysis. Thus, it is recommended to also document the hazards that were not considered as critical. 

Before any mitigation measures can be designed, an effective hazard identification study must be conducted. The results of such a study (a set of release scenarios) can be used to develop a coherent set of mitigation strategies. In the process industries, these studies are most commonly conducted using hazard and operability (HAZOP) studies, what-if checklists, failure modes and effects analyses (FMEA), and several other comparable techniques (CCPS, 1992). 

Chapters bear titles such as, Preparing for Hazards Evaluation Studies, Hazards Identification Methods and Results, and Selecting Hazard Evaluation Techniques. Supplemental Questions for Hazards Evaluation in Appendix B is excellent. Appendix B contains some of the important questions that are not thought of when performing a HAZOP study. There are 45 pages of probing questions on the process, specific classes of equipment, operation and maintenance, and hazard searching review. List price 120. 

NUS Corp., HAZOP Study Team Training Manual. Predictive Hazard Identification Techniques for Dow Corning Facilities, Gaithersburg, MD (July 1989). 

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