Uncertainty, acceptable risk

The determination of an acceptable dose for humans involves the application of uncertainty factors to reflect the fact that, unlike the experimental animal, there is wide variability and susceptibility of response in the genetically diverse human population. Variations in gender, age, hormonal and disease status can affect the response to a chemical. In order to minimise any potential risks, uncertainty factors are applied to the NOAEL to arrive at a reduced exposure that is considered tolerable - namely the acceptable daily intake or ADI. These are usually tenfold for variations in susceptibility amongst the human population (the intra-species factor) and tenfold for the potential... 

FIGURE 8.1 The risk curve lines shown represent thresholds between different types of decisions (based on ECOFRAM 1999a and 1999b). These thresholds would be determined by decision makers and may move location subject to other factors that affect the decision (e.g., pesticide benefits). The bottom graph shows an example risk curve with uncertainty bounds. The curve clearly fits within the acceptable risk category however the upper uncertainty bound does not, indicating a need for risk mitigation or further refinement of the risk assessment. 

In a screening-level risk assessment, interval or bounding analyses, which put upper and lower bounds on risk, may be sufficient to reach a decision of acceptable risk or unacceptable risk provided the bounds are a reflection of the true limits of uncertainty. 

We fully recognize that many areas of uncertainty are confronted when conducting risk assessments. These include the lack of generally accepted specific assessment techniques. Furthermore, even when risk is assessed there is a lack of a consensus on the absolute limits of acceptable risks. We do feel, however, that there are systematic approaches that can and are being used and, at the minimum, they are directionally correct and can serve as a conceptual framework for regulatory program development. 

Although the benefits of pesticides are undeniable, attention in recent years has been focused on their impact on human health and environment. Although pesticide law requires that both risks and benefits be considered in all decisions, risk drives the process in terms of depth of analysis and allocation of federal resources. Two questions relative to risk are appropriate "What is acceptable risk " and "How can we minimize the risk . No amount of research can eliminate all uncertainties associated with assessing the risks of exposure to pesticides or eliminate the controversial judgments inherent in any decision about control of pesticide exposures. 

There are difficult policy decisions and unresolved scientific issues in the testing of carcinogenic risk of chemicals to humans. There has been considerable discussion on how to define an acceptable risk for populations exposed typically to low doses of environmental carcinogens. The relevance of animal results to man, and methods of extrapolation, appears to he more appropriate to handle living with uncertainty. 

Many risks people are subjected to can cause health problems or death. Precautions should be taken based on what is practical, logical, and useful. However, those involved in laws and regulations, as well as the public and, particularly, the news media, should recognize that there is Acceptable Risk. This is the concept that has developed in connection with toxic substances, food additives, air and water pollution, fire and related environmental concerns, and so on. It can be defined as a level of risk at which a seriously adverse result is highly unlikely to occur but it cannot be proven whether or not there is 100% safety. In these cases, it means living with the reasonable assurance of safety and acceptable uncertainty. This concept will always exist. Note the use of automobiles, aircrafts, boats, lawnmowers, food, medicine, water, and the air we breathe. Practically all elements around us encompass some level of uncertainty. Otherwise, life as we know it would not exist. Many products and environmental factors are not perfect and never will be perfect. 

In a)-d) a key issue to address is how the frameworks take into accoimt that the different stakeholders involved could have different perspectives on risk, uncertainties and acceptability. To what extent do the frameworks acknowledge this diversity in perspectives and what means do they offer to deal with it ... 

Figure 3-7 illustrates the issue. There is a region in which all will agree on what is safe. There are conditions, behaviors, and circumstances that all will agree are not safe. Between those two zones is a region of uncertainty. Someone must decide how far to move the boundary of acceptable risk. 

The main uncertainty in deterrnitiing the societal risk is limited knowledge regarding the number of people affected by events following disruption of the gas pipeline. Also the estimated degree of protection of people inside the buildings and vehicles is uncertain. These factors become even more important when the calculated societal risk is close to the limit of acceptable risk. 

Risk and uncertainty associated with each venture should translate, ia theory, iato a minimum acceptable net return rate for that venture. Whereas this translation is often accompHshed implicitly by an experienced manager, any formal procedure suffers from the lack of an equation relating the NRR to risk, as well as the lack of suitable risk data. A weaker alternative is the selection of a minimum acceptable net return rate averaged for a class of proposed ventures. The needed database, from a collection of previous process ventures, consists of NPV, iavestment, venture life, inflation, process novelty, decision (acceptance or rejection), and result data. 

The. statement goes on to acknowledge the contribution of the Reactor Safety Study (WASH-1400) to risk quantification but points out that safety goals were not the study objectives and that the uncertainties make it unsuitable for such a purpose. After pointing out that the death I f any individual is not "acceptable," it states two quantitative objectives ... 

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