Hazard and operability method

Prior to stan-up of i production campaign, a process hazards analysis (PHA) should be conducted. A common and generally accepted PHA technique is the HAZOP (Hazard and Operability) method, although alternate teehniques can he equally effective 113.14,l.s, The purpose of the PHA is to evaluate the maiuiltictiiring prtteess to identity aiul address potential safely issues prior to start-up. 

Although companies in the process industries have always worked on the identification and control of hazards, the formal discipline of PHA, specifically the HAZOP (Hazard and Operability) method, was not developed until the 1960s by process plant professionals in the United Kingdom, many of whom worked for the company ICI (Lawley, 1976 Knowlton, 1992 Kletz, 1997). More recent guidance is provided in ISO 17776 (2000). 

Another well-known technique of hazard identification is the HAZOP (HAZard and OPerability) method. With this method, hazards are identified and analyzed using sessions with operational experts. At the same time, the experts come up with potential solutions and measures to cope with the identified hazards (Kletz, 1999). The advantage of HAZOP with respect to the functional approach is that also nonfunctional hazards are identified during the brainstorm with operational experts. However, in applying HAZOP, one needs to take care that hazard analysis and solution activities do not disturb the hazard identification process, which could leave certain hazards unidentified or inappropriately solved . Leaving such latent hazards in a design typically is known to be very costly in safety critical operation. 

Conduct a Hazards Analysis. The technique chosen is likely to be the Failure Modes and Effects Analysis (FMEA) for drilling rigs, and a Hazard and Operability Method (HAZOP) for production platforms that are already in operation. 

Analyzing the behavior of a process in case of a malfunction of one or more process elements is a time consuming and difficult task. Therefore, great effort was spent designing supporting systems for this problem. Most of the systems apply standard hazards analysis methods like the HAZOP (Hazard and Operability) method. In HAZOP analysis a team of experienced people analyses each process element in terms of possible failure and the effect of this failure on the rest of the process. The method is clearly structured by a syntax of its own and therefore well suited for use in expert systems. 

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. 

FIAZOP is a formally struetured method of systematieally investigating eaeh element of a system for all ways where important parameters ean deviate from the intended design eonditions to ereate hazards and operability problems. The HAZOP problems are typieally determined by a study of the piping and instrument diagrams (or plant model) by a team of personnel who eritieally analyze eflfeets of potential problems arising in eaeh pipeline and eaeh vessel of the operation. 

The what-if analysis is a creative, brainstorming examination of a process or operation conducted by a group of experienced individuals able to ask questions or voice concerns about undesired events. It is not as inherently structured as some other methods, such as the hazard and operability (HAZOP) study or a failure mode and effects analysis (FMEA). 

V Process hazard analysis (PHA) must be performed by a team of experts, including engineers, chemists, operators, industrial hygienists, and other appropriate and experienced specialists. The PHA needs to include a method that fits the complexity of the process, a hazards and operability (HAZOP) study for a complex process, and for less complex processes a less rigorous process, such as what-if scenarios, checklists, failure mode and effects analysis, or fault trees. 

Another widely used safety analysis method in process industry is the Hazard and Operability Analysis, better known as Hazop (Kletz, 1992). The conventional Hazop is developed to identify probable process disturbances when complete process and instrumentation diagrams are available. Therefore it is not very applicable to conceptual process design. Kletz has also mentioned a Hazop of a flowsheet, which can be used in preliminary process design, but it is not widely used. More usable method in preliminary process design is PIIS (Edwards and Lawrence, 1993), which has been developed to select safe process routes. 

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. 

Kennedy R., Kirwan B., 1998. Development of a Hazard and Operability-based method for identifying safety management vulnerabilities in high risk systems, Safety Science 30, pp. 249-274. 

Many different loss event scenarios are possible with intentional chemistry. All of them relate to losing containment or control of the intended reaction, starting another reaction, side reaction or series of reactions that are not intended or expected. A process hazard analysis, using a hazard and operability (HAZOP) study or other appropriate method, should be used to systematically identify and evaluate a full set of loss event scenarios. General causes of uncontrolled reactions include, but are not confined to, the following list ... 

For larger or more complex facilities, a systematic approach to identifying incompatibility scenarios and analyzing their severities and likelihoods may be warranted. A process hazard analysis (PHA) approach such as a hazard and operability (HAZOP) study can be an effective tool to facilitate such an effort, and may be required by regulation if the process falls within the scope of regulations. These methods are discussed in Section 4.5. 

Mosley et al. (2000) describe a "chemistry hazard analysis" approach, similar to a hazard and operability (HAZOP) study method applied at the early development stages of a new process. Deviations from an intended chemical reaction are identified using typical HAZOP guidewords. Examples of deviations and consequences developed using this approach are shown in Table 4.10. Analyzing the basic chemistry of a process, where chemical reactions are intended to occur, can help ensure the consequences of deviating from the intended reaction are understood. 

Hazard and operability (HAZOP) study, screening methods, 38-39, 63... 

Hazard and Operability Studies (HAZOP) Other methods... 

If there is no hypothesis for the event, use an inductive method to find potential scenarios. Inductive methods speculate a given fault or failure, then look forward in time to determine the probable outcome, that is, What would happen if... Inductive methods include using a Checklist or a Hazard and Operability Analysis (HAZOP). 

Process Hazard Analysis (PHA) can be defined as the application of a systematic method to a process design in order to identify potential hazards and operating problems. It determines the causes and consequences of abnormal process conditions that arise from equipment failure, human error or other events. The goal is to determine whether opportunities exist to reduce the risks of the toll s hazards and then to implement warranted action items. The AJChE CCPS guideline Guidelines for Hazard Evaluation Procedures, Second Edition with Worked Examples is a good resource for fully detailed approaches to process hazard analysis. It provides an introduction to hazard evaluation as well as guidance on ... 

Hazard and risk analysis is a vast subject by itself and is extensively covered in the literature [22]. In order to plan to avoid accidental hazards, the hazard potential must be evaluated. Many new methods and techniques have been developed to assess and evaluate potential hazards, employing chemical technology and reliability engineering. These can be deduced from Fault Tree Analysis or Failure Mode Analysis [23], In these techniques, the plant and process hazard potentials are foreseen and rectified as far as possible. Some techniques such as Hazards and operability (HAZOP) studies and Hazard Analysis (HAZAN) have recently been developed to deal with the assessment of hazard potentials [24]. It must be borne in mind that HAZOP and HAZAN studies should be properly viewed not as ends in themselves but as valuable contributors to the overall task of risk management... 

Methods for performing hazard analysis and risk assessment include safety review, checklists, Dow Fire and Explosion Index, what-if analysis, hazard and operability analysis (HAZOP), failure modes and effects analysis (FMEA), fault tree analysis, and event tree analysis. Other methods are also available, but those given are used most often. 

Process Hazards Analysis. Analysis of processes for unrecognized or inadequately controlled hazards (see Hazard analysis and risk ASSESSMENT) is required by OSHA (36). The principal methods of analysis, in an approximate ascending order of intensity, are what-if checklist failure modes and effects hazard and operability (HAZOP) and fault-tree analysis. Other complementary methods include human error prediction and cost/benefit analysis. The HAZOP method is the most popular as of 1995 because it can be used to identify hazards, pinpoint their causes and consequences, and disclose the need for protective systems. Fault-tree analysis is the method to be used if a quantitative evaluation of operational safety is needed to justify the implementation of process improvements. 

The HAZOP Study is a very popular predictive method which was developed in the Mond Division of Imperial Chemical Industries during the 1960s. A HAZOP (Hazard and Operability) study is an analysis method for identifying hazards and problems which prevent efficient operation. Trevor Kletz was an early promoter of the HAZOP Method and in one of his recent books [18], he states ... 

A Hazard and Operability study (HAZOP) is the preferred method, in the process industries, of identifying hazards on new or existing plants. 

Robert Johnson presented a technical paper in April 1992 entitled HAZOPS Today [19] in which he stated, The hazard and operability studies (HAZOPS) method has likely become, over a period of less than ten years, the most widely-used hazard evaluation procedure in the process industries. Johnson also explained that HAZOPS is a relative latecomer to the United States and it has attained a high degree of prominence in the U.S. process industries. The method began in the United Kingdom and has now spread throughout western Europe and North America. (See Figure 11—1.)... 

This publication is intended to provide guidance to HAZOP (Hazard and Operability) and What-If review teams associated with the petroleum and chemical industries. It describes the nature, responsibilities, methods and documentation required in the performance of such reviews. 

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. The Chemical Industries Association has published a Guide to Hazard and Operability Studies, CIA (1979b), which gives a comprehensive description of the technique and examples of its application. The method is also explained fully by Kletz (1999). Further examples are given by Lawley (1974), Wells (1980) and Austin and Jeffreys (1979). 

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