Failure condition, fault hazard analysis

The Process Hazards Analysis team takes a systematic approach to identify potential process hazards and to document them [51]. The Hazardous-Operation Analysis (Haz-Op) is a method by which the process procedures, process and instrument diagrams, and process flow diagrams are evaluated for operability and safety. Fault-Tree Analysis (FTA) is also a method, which investigates the assessment of what-if scenarios and failure conditions. The outcomes of this analysis are recommendations for the col-... 

Identify hazardous chemicals from databases as discussed in Section 16.4.4 and from local legal regulations. Identify the potential for hazards from the checklist for reactivity (in Section 16.4.4) and from HAZOP-type studies or fault-tree analysis (Crowl and Louvar, 1990). In HAZOP studies, use checklist key words as triggers to systematically analyze the impact of changes to flow rate, temperature, pressure, composition, level, viscosity, heat transfer, reaction, and conditions and the potential for barrier failure and startup and shutdown to cause hazards. 

The SSHA evaluates hazardous conditions, on the subsystem level, which may affect the safe operation of the entire system. In the performance of the SSHA, it is prudent to examine previous analyses that may have been performed such as the preliminary hazard analysis (PHA) and the failure mode and effect analysis (FMEA). Ideally, the SSHA is conducted during the design phase and/or the production phase, as shown in Chapter 3, Figure 3.4. However, as discussed in the example above, an SSHA can also be done during the operation phase, as required, to assist in the identification of hazardous conditions and the analysis of specific subsystems and/or components. In the event of an actual accident or incident investigation, the completed SSHA can be used to assist in the development of a fault tree analysis by providing data on possible contributing fault factors located at the subsystem or component level. 

Model Based Safety Assessment aims at supporting the Preliminary System Safety Assessment (PSSA) [8]. Before the PSSA is performed, the Functional Hazard Analysis identifies the Failure Conditions (e.g. safety critical situations of the system) and assesses their severity on a scale going from No Safety Effect (NSE) to Catastrophic (CAT). Then, during the Preliminary System Safety Assessment, safety models (or alternatively fault-trees) axe built and analysed. A safety model describes formally in which node a fault occurs and how this fault propagates inside the system architecture in order to cause a Failure Condition. 

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). 

CONSTRUCTING THE FAULT TREE. Fault tree construction begins at the top event and proceeds, level by level, until all fault events have been traced to their basic contributing events or basic events. The analysis starts with a review of system requirements, function, design, environment, and other factors to determine the conditions, events, and failures that could contribute to an occurrence of the undesired top event. The top event is then defined in terms of sub-top events, i.e., events that describe the specific "whens and wheres" of the hazard in the top event. Next, the analysts examine the sub-top events and determine the immediate, necessary, and sufficient causes that result in each of these events. Normally, these are not basic causes, but are intermediate faults that require further development. For each intermediate fault, the causes are determined and shown on the fault tree with the appropriate logic gate. The analysts follow this process until all intermediate faults have... 

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