Risk-based approach disadvantages

In conclusion, although the OLF-070 guidelines much the same principles as lEC 61508/61511 the main difference is the initial determination of integrity levels. Whereas the lEC standard defines a risk based approach, the OLF-070 guideline attempts match the safety instrumented functions to common typical loops and assign a minimum integrity level. The disadvantage of this approach is that the demand rate, severity, and personnel exposure to the hazard are not... 

Disadvantages/limitations of the risk-based approach include ... 

This option does not appear to be advantageous for either radionuclides or chemicals that cause stochastic responses. In radiation protection, total detriment is used mainly to develop the tissue weighting factors in the effective dose (see Section 3.2.2.3.3), but ICRP and NCRP have continued to emphasize fatal responses as the primary health effect of concern in radiation protection and radiation risk assessments. Since total detriment is based on an assumption that fatalities are the primary health effect of concern, the same difficulties described in the previous section would occur if this measure of response were used for chemicals that induce stochastic responses. Other disadvantages of using total detriment include that detriment is not a health-effect endpoint experienced by an exposed individual and the approach to weighting nonfatal responses in relation to fatalities is somewhat arbitrary. Furthermore, total detriment is not as simple and straightforward to understand as either incidence or fatalities. 

This approach often has the disadvantage of being a qualitative decision, based on available data and circumscribed by the experience of the participants. Written rationales are often missing, on less than adequate, for further peer or legal review. The consensus approach does, however, allow for a strong introduction of "rational" common sense, qualitative risk assessment, etc. to be introduced into the decision making process. Many of our existing health and safety environmental standards were developed on this approach. 

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