Acceptable risk described

Risk is the product of the probability of a release, thepjpbability of exposure, and the consequences of the exposure. Risk is usually described graphically, as shown in Figure 11-15. All companies decide their levels of acceptable risk and unacceptable risk. The actual risk of a process or plant is usually determined using quantitative risk analysis (QRA) or a layer of protection analysis (LOPA). Other methods are sometimes used however, ORA and LOPA are the methods that are most commonly used. In both methods the frequency of the release is determined using a combination of event trees, fault trees, or an appropriate adaptation. 

The accepted risk is a risk inferior to a level defined in advance either by law, technical, economical, or ethical considerations. The risk analysis, as it will be described in the following sections, has essentially a technical orientation. The minimal requirement is that the process fulfils requirements by the local laws and that the risk analysis is carried out by an experienced team using recognized methods and risk-reducing measures that conform to the state of the art It is obvious that non-technical aspects may also be involved in the risk acceptation criteria. These aspects should also cover societal aspects, that is, a risk-benefit analysis should be performed... 

It is the physician s responsibility to inform the patient of the risk of immunization and to employ vaccines and antisera in an appropriate manner. This may require skin testing to assess the risk of an untoward reaction. Some of the risks described above are, however, currently unavoidable on the balance, the patient and society are clearly better off accepting the risks for routinely administered immunogens (eg, influenza and tetanus vaccines). 

Based on the assumptions described above, the risk calculated using the RESRAD code (Yu etal., 1993) and EPA slope factors (HEAST, 1991 1995) is a probability of cancer incidence of about 7 X 10 4. The assumed acceptable risk for low-hazard waste is 10 3 (see Table 7.1), resulting in a risk index of 0.7. Hence, domestic uranium mill tailings could be classified as low-hazard waste acceptable for licensed near-surface disposal under conditions of perpetual institutional control over disposal sites. 

Based on the assumptions described above, the results of the calculation of stochastic risk for all hazardous chemicals in the waste are shown in Table 7.9. From the calculated lifetime risk of 1.7 X 10 5 and the assumed acceptable risk of 10 3, the risk index for all hazardous chemicals that cause stochastic effects is (1.5 X 10 5)/10 3, or about 0.02. Thus, based only on consideration of these substances, the waste would be classified as low-hazard. 

The primary reason to oppose the filling of the car s gas tank, as it was deceptively, but accurately, described, is simply because it violates the safe practices that has been adopted as standard. The initial question, Would it be an acceptable risk cannot be answered yes based solely on the information given. One would need either to understand the physics, design standards, and routine testing that make fill-up s safe, or to rely on history, which indicates low probability of incident. Without this knowledge, one would have to be conservative and say that gas tank fill-up, as described, is not an acceptable, safe practice. 

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. 

If risks are classified as tolerable, or if there is dispute as to whether they are tolerable or acceptable, risk management needs to design and implement actions that make these risks acceptable over time. Should this not be feasible then risk management, assisted by communication, needs at least to credibly convey the message that major effort is undertaken to bring these risks closer to being acceptable. This task can be described in terms of classic decision theory (Morgan 1990 Hammond et al. 1999). 

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. 

These levels can be described as unacceptable , tolerable , and broadly acceptable risk [16]. 

The RAC matrix and the risk acceptability criteria described in this example are representative of many of the risk assessment efforts presently in use and are consistent with the MIL-STD-882B approach to risk assessment. 

Part of the risk acceptance process is a methodical decision-making approach. If the risks are not acceptable, then the system must be modified and the hazard identification process must be followed once again. If the risks are acceptable, then good documentation with written rationale is imperative to protect against liability claims. Chapters 13 and 14 address these issues in depth. Some people will use the term risk appetite to describe this process. The very first step—define objectives— should clearly define what is an acceptable risk (risk tolerance or risk appetite) that the company is willing to accept. 

In ti the state of material degradation is acceptable (green state) and this leads to an optimal value of loss of containment risk, described by the white color. 

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