Post-Challenger Evaluation of Space Shuttle Risk Assessment and Management (1988) / Chapter Skim
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Appendix D: Probabilistic Risk Assessment
Appendix D: Probabilistic Risk Assessment
Pages 115-124
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From page 115... ...
be the results from the various safety, reliability, and quality assurance programs of the field offices. The transformation of this information into a useful basis for decision making is the step that enables meaningful risk management to occur.
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From page 116... ...
The document, which might be called the Risk Summary Report, would be updated regularly and might be the basic document upon which the risk management function would draw. It would contain in an organized way the combined knowledge of the entire technical team on issues of risk.
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From page 117... ...
If the information machine is properly constructed, it establishes not only an orderly caTcuRISK SUMMARY REPORT PROJ ECT ~6 ^~ MANAGEMENT ~ ~3 DECISION-MAKING ~ rating and recording mechanism but, perhaps even more importantly, it establishes a language and a conceptual framework that unifies and organizes the thinking, communication, and decision making of the whole project. Not only are better design decisions thus made, but enormous savings in time and talent can result simply from the fact that everybody is using the same language so that, to a great extent, all participants mean the same things by the same words.
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From page 118... ...
These curves are called state of knowledge curves. They become the final quantitative expression of risk and reliability.
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From page 119... ...
5.3 Structuring and Categorizing the Triplets Since the number of possible scenarios for a system can be very large, it is important in carrying out a Probabilistic Risk Assessment (PRA) to or ganize and categorize the set of triplets.
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From page 120... ...
5.6 Assembly and Disassembly of Risk 5.6.1 Identifying Scenarios According to the definition of risk noted above, the first and most important step in risk assessment is to identify the scenarios. In this connection, the following are some key ideas.
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From page 121... ...
" This approach would seem to be particularly appropriate for space systems. "Parts" could be interpreted successively as physical segments of the total system, as functional subsystems in the system; they could also mean different phases of the system's mission life.
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From page 122... ...
The fact that this qualitative information can be quantified as a probability density is the ma jor result of the theory of sub jective probability that has been developed since the 1950's. The second ingredient is the `'1ikelihood function" associated with the available data that contains information about Aj.
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From page 123... ...
If one now recognizes that, in the course of such a stucly and analysis, many areas of the design or maintenance/operation practices will surely be discovered where we can do L' better, and if those improvements are then implementecl, the probability curve will change again, hopefully to something like the curve P2 in Figure D-10. With repeated cycles of this type of analysis and with continued experience and technology improvement, one may hope ultimately to achieve something like curve P3, which perhaps is what is needed to support a viable manned space program.
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