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Quantitative Assessment

In any discussion of mishap risk management and risk assessment, the question of quantified acceptability parameters arises. Care should be exercised, under such conditions not to forget the limitations of a mathematical approach. In any high-risk system, there is a strong temptation to rely totally on statistical probability because, on the surface, it looks like a convenient way to measure safety "who can argue with numbers" To do so, however, requires that the limitations and principles of this approach are well understood and that past engineering experience is not ignored. Quantitative acceptability parameters must be well defined, predictable, demonstrable, and above all, useful. They must be useful in the sense that they can be easily related to the design and the associate decision criteria


Many factors fundamental to system safety are not quantifiable. Design deficiencies are not easily examined from a statistical standpoint. Additionally, the danger exists that system safety analysts and managers will become so enamored with the statistics that simpler and more meaningful engineering processes are ignored. Quantification of certain specific failure modes, which depend on one of two system components, can be effective to bolster the decision to accept or correct it.


General risk management principles are:

a. All human activity involving a technical device or process entails some element of risk.

b. Most hazards (safety risks) can be neutralized or controlled.

c. Hazards should be kept in proper perspective. Weighing the risk does this by knowledge gained through analysis and experience against program need.

d. System operations represent a gamble to some degree; good analysis assists the MA in controlling the risk.

e. System safety analysis and risk assessment does not eliminate the need for good engineering judgment.

f. It is more important to establish clear objectives and parameters for risk assessment than to find a cookbook approach and procedure.

g. There is no "best solution" to a safety problem. There are a variety of directions to go. Each of these directions may produce some degree of risk reduction.

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