Hazards, nature event trees

A systems hazards analysis (SHA) is a systematic and comprehensive search for and evaluation of all significant failure modes of facility systems components that can be identified by an experienced team. The hazards assessment often includes failure modes and effects analysis, fault tree analysis, event tree analysis, and hazards and operability studies. Generally, the SHA does not include external factors (e.g., natural disasters) or an integrated assessment of systems interactions. However, the tools of SHA are valuable for examining the causes and the effects of chemical events. They provide the basis for the integrated analysis known as quantitative risk assessment. For an example SHA see the TOCDF Functional Analysis Workbook (U.S. Army, 1993-1995). 

THERP can also be used for event tree modeling. For example, an initiating event could be an emergency situation such as a leak of a hazardous chemical. Items in the event tree that could incorporate human error include recognition that a leak has occurred, identifying the nature of the leak, and using the correct emergency response equipment. 

With proper equipment and suiting attempt to control and contain tlie hazardous material, fire, or other event. Consider tlie nature and quantity of tlie material tliat could be im-olved in your response to tlie situation. See literature and Chem Tree or manufacturer on how to attack the problem with safety... 

The major input requirement for a fault tree analysis is the top event. The nature of the undesired top event must be provided based on an earlier hazard analysis (formal or informal) and/or historical data. 

The first step in performing a fault tree analysis is to collect the appropriate project description documents, existing hazard analyses, and guidance documents and carefully review them to determine the limits, scope, and ground rules for the FTA.This review includes defining the system to be analyzed, the depth or indenture levels to be included in the effort, and, of course, the nature of the undesired event or failure to be studied. 

FTA is a tool employed in the analysis of complex systems to estimate the likelihood of a hazardous event. It has been applied, for example, in safety evaluations of nuclear power plants, space missions, air, rail, highway, marine and pipeline transport, liquefied natur gas, chemical manufacturing, and other hazardous material facilities. With this method, all material, personnel, and environmental factors of a complex system can be systematically presented. A well-constructed fault tree enables us to discover failure combinations that would not normally be discovered and provides for both qualitative and quantitative evaluation. 

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