Process hazard analysis dependability

The experts are the members providing the technical expertise for completing the study. Depending upon the process, a process hazard analysis could include any or all of the following types of experts. Some can be brought in on an as needed basis ... 

There are many different methodologies under the Process Hazards Analysis (PHA) umbrella. Depending on the goals of the study and the time available, one of several different studies would be completed. One of the most comprehensive PHAs is a HAZOP (Hazards and Operability Study), which identifies operability problems as well as hazards to personnel, company property, and the environment. 

Various analytical tools can be used in conjunction with the JHA process. These are used for specific purposes or conditions depending on the industry and range widely complexity. Examples would include — Process Hazard Analysis," What-If Analysis and Checklists for scenario development. Hazard and Operability Studies (HAZOP), Failure Mode and Efiect Analysis (FMEA), Fault-tree Analysis, Activity Hazard Analysis (Appendix H). 

There are a large number of standard methods suitable for each stage in the hazard analysis and risk assessment procedure. The selection of the proper method depends on several factors. Some of these are the type of process, the stage in the lifetime of the process, the experience and capabiUties of the participants, and the step in the procedure that is being examined. Information regarding the selection of the proper procedure is available in an excellent and comprehensive reference (1). 

Experimental analysis involves the use of thermal hazard analysis tests to verify the results of screening as well as to identify reaction rates and kinetics. The goal of this level of testing is to provide additional information by which the materials and processes may be characterized. The decision on the type of experimental analysis that should be undertaken is dependent on a number of factors, including perceived hazard, planned pilot plant scale, sample availability, regulations, equipment availability, etc. 

The basic objective of hazard analysis is to identify and assess potentially hazardous situations, and their possible consequences and associated risk, in order to provide a rational basis for determining where risk reduction measures are needed. Hazard identification always has been an integral part of design and operational practice. However, it is to a large degree still an informal process depending on the experience of those directly involved. 

Hazard analysis for a process normally involves a battery of tests including Differential Scanning Calorimetry (DSC) and Accelerating Rate Calorimetry (ARC). Optimization and scale-up also require extensive experimental work in reactors of different sizes with different temperatures, compositions, etc. Time commitment and difficulty in interpreting the results will depend on the complexity of the process. Under most circumstances, a modeling approach is cost-effective (1 ). The importance of modeling will actually increase with the increasing complexity of the process. 

The sampling procedure used will obviously depend on the type of sample whether it is liquid or solid fresh, chilled or frozen and the type of container e.g. tinned, bottled). Other major problems are the frequency of sampling and the position on a production line from which a sample is taken. For example, when sampling from a food production line is carried out, an important consideration is whether or not the food has been subjected to sterilisation, or any form of pasteurisation after the point from which the sample was taken. This is considered further in the chapter on food microbiology under the concept of Hazard Analysis Critical Control Point (HACCP). Whatever the form of the sample, it should be collected in a sterile container using aseptic techniques, returned to the laboratory under conditions identical to those from which it was taken, and processed as rapidly as possible. 

The workflow should be broken down to manageable chunks each of which become a target for a round of hazard analysis and perhaps our what-if questions. It is at this stage that detailed hazards, causes and controls can be established which will form the bulk of the hazard register. The system business processes themselves may be derived from a number of different sources depending on the material available. Some systems may have detailed use cases with primary and exception flows carefully documented. For others the processes may need to be ascertained from training material, product descriptions or test cases. 

Unfortunately, no tools exist for identifying hazards. It takes domain expertise and depends on subjective evaluation by those constructing the system. Chapter 13 in Safeware provides some common heuristics that may be helpful in the process. The good news is that identifying hazards is usually not a difficult process. The later steps in the hazard analysis process are where most of the mistakes and effort occurs. 

STPA (System-Theoretic Process Analysis) can be used at any stage of the system life qrcle. It has the same general goals as any hazard analysis technique accumulating information about how the behavioral safety constraints, which are derived from the system hazards, can be violated. Depending on when it is used, it provides the information and documentation necessary to ensure the safety constraints are... 

Because operational safety depends on the accuracy of the assumptions and models underlying the design and hazard analysis processes, the operational system should be monitored to ensure that ... 

Before any planned changes are made, including organizational and safety control structure changes, their impact on safety must be evaluated. Whether this process is expensive depends on how the original hazard analysis was performed and particularly how it was documented. Part of the rationale behind the design of intent specifications was to make it possible to retrieve the information needed. 

The approach used to identify hazards will depend on the application being considered. For certain simple processes where there is extensive operating experience of a standard design, such as simple off-shore wellhead towers, it may be sufficient to use industry developed check lists (for example, the safety analysis checklists in ISO 10418 and API RP 14C). Where the design is more complex or a new process is being considered, a more structured approach may be necessary (for example, lEC 60300-3-9 1995). 

The ETBA is an analytical technique that can be of great assistance in preparation of the preliminary hazard list (PHL). It can also be quite useful in the development of a preliminary hazard analysis (PHA), subsystem hazard analysis (SSHA), or the more general system hazard analysis (SHA). The ETBA can also be used, depending on the specific system under consideration, in the development of the operating and support hazard analysis (O SHA), and, of course, during the MORT process from which the ETBA evolved. 

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