Acceptable risk examples

Most people will tolerate greater risk from activities when the threat to life is offset in time from when the risk (and the benefit) is originally accepted. For example, people may feel worse (and usually accept less risk) about a threat of immediate harm (e.g., the blast wave from an explosion) than a threat of latent harm (e.g., an increase in the chance of getting a fatal disease following a 20-year exposure to a hazardous material, like asbestos), even though the risks may be equivalent. 

Reduction of Inventories Advancements in process control and changing acceptable risk standards may have removed the initial justification for large inventories of hazardous raw materials or products. For example, tight quality control of on-time deliveries of hazardous raw materials may allow for a one or two day supply on hand versus a one- or two-week supply. 

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. 

The adverse event needs to be clinically significant enough that the risk-benefit of therapy is percieved to be altered. In this regard, the acceptable risk-benefit profile of anti-cancer therapies is markedly diflFerent than, for example, that of anti-hypertension therapy. 

Everyone faces varying degrees of risks at home, in the workplace or on the road. An example of an acceptable risk would be an act almost everyone of us performs many times a week opening our mail. Have you ever got a cut while tearing open... 

Figure 1.2 Example risk diagram with the accepted risk in white, non-accepted risk in dark gray, and conditionally accepted risks in light gray.

Acceptable risks or doses for radionuclides and chemical carcinogens also could be established based on considerations of unavoidable risks from natural background as noted previously, these lifetime risks are about 10 2. For example, an acceptable risk could be set at a value corresponding approximately to the geographical variability in the background risk, because people normally do not consider this variability in deciding where to live. 

Section 7 then addresses the implications of the recommended risk-based waste classification system. By assuming key parameters (e.g., values of acceptable risk, characteristics of exposure scenarios) and applying the system to a variety of example waste streams, the question of how existing wastes would be classified in the new system is investigated. This Section also summarizes the legal and regulatory ramifications of the proposed hazardous waste classification system. 

In many respects, the foundations and framework of the proposed risk-based hazardous waste classification system and the recommended approaches to implementation are intended to be neutral in regard to the degree of conservatism in protecting public health. With respect to calculations of risk or dose in the numerator of the risk index, important examples include (1) the recommendation that best estimates (MLEs) of probability coefficients for stochastic responses should be used for all substances that cause stochastic responses in classifying waste, rather than upper bounds (UCLs) as normally used in risk assessments for chemicals that induce stochastic effects, and (2) the recommended approach to estimating threshold doses of substances that induce deterministic effects in humans based on lower confidence limits of benchmark doses obtained from studies in humans or animals. Similarly, NCRP believes that the allowable (negligible or acceptable) risks or doses in the denominator of the risk index should be consistent with values used in health protection of the public in other routine exposure situations. NCRP does not believe that the allowable risks or doses assumed for purposes of waste classification should include margins of safety that are not applied in other situations. 

This Section provides example applications of the recommended risk-based waste classification system to a variety of hazardous wastes to illustrate its implementation and potential ramifications. Disposal is the only disposition of waste considered in these examples. In Section 7.1.1, a general set of assumptions for assessing the appropriate classification of hazardous wastes is developed, including a variety of assumed exposure scenarios for inadvertent intruders at waste disposal sites and assumed negligible and acceptable risks or doses from exposure to radionuclides and hazardous chemicals. Subsequent sections apply the methodology to several example wastes. 

An acceptable risk is one which people instinctively consider to be so small that they never seriously worry about it. In northern latitudes, the risk arising from being struck by lightning might be an example few people lie awake at night fretting about it. 

However, it is also common to use standards to set up the infrastructure, policies, controls, or rules that mean that incidents and risks occur with acceptably rare probabilities. These standards might be described as strategic standards. For example, controls on ammonia in sewage treatment works (which are back-calculated from environmental standards) are designed to promote good fisheries in the receiving river. The intention is to reduce serious incidents to an acceptable frequency in each river because the infrastructure of sewage treatment appears to function at this level of acceptable risk. This may result in a compromise, which is essentially that standards are set up as particular types of summary statistics and not as absolute limits. 

Risks that involve no apparent benefit to the individual are, understandably, less likely to be acceptable. For example, the possibility of traces of a poUutant like dioxin in an incinerator exhaust (where the incinerator may be producing heat or power for a community and removing waste) would be unacceptable to many people. 

In its simplest form, risk assessment asks, How much exposure can we allow without causing irreparable harm Harm to whom Initially, to a maximally exposed individual and more recently to a sensitive and maximally exposed individual. For example, to keep chemical contamination to acceptable levels in a river, EPA would define acceptable risk to a maximally exposed individual. Acceptable risk would be defined as an exposure to a contaminant below its threshold for causing damage or, more often, a one-in-a-million risk of getting cancer from a... 

It is my hope that this book can define a very complex problem and describe solutions. The examples of dioxin cleanup issues and procedures are offered to provide engineers, health scientists, regulators, lawyers, business people, and other concerned individuals with a methodology applicable to other hazardous chemicals. I believe that science can detect pollutants in the environment and estimate their potential health risk. Society as a whole, scientist and nonscientist, determines acceptable risk. Society also plays a major role in managing risk because we face many problems and have limited resources to deal with them all. 

For example, the Ontario risk assessment uses a no observable effect level (NOEL) of 0.001 ug/kg/day (6.73) and a safety factor of 100 to obtain a maximum allowable dally intake of 1 X 10" 1 g/kg/day (= 10 pg/kg/day) for humans (74). In contrast, EPA has used a value of 6.4 X 10" 5 g/kg/day which suggests cancer risks that are 1670 fold higher. The United States Food and Drug Administration (FDA) has, on the other hand, accepted risks associated with the ingestion of up to 13 pg/kg/day. (Table IX). 

Safety-related constraints should have two-way links to the system hazard log and to any analysis results that led to that constraint being identified as well as links to the design features (usually level 2) included to eliminate or control them. Hazard analyses are linked to level 1 requirements and constraints, to design features on level 2, and to system limitations (or accepted risks). An example of a level 1 safety constraint derived to prevent hazards is ... 

Limitations are often associated with hazards or hazard causal factors that could not be completely eliminated or controlled in the design. Thus they represent accepted risks. For example,... 

---