Acceptable or Tolerable Risk

In every walk of life there is a certain amount of risk. The same can be said for manufacturing and mining processes. It is financially and physically impossible to eliminate aU risks from aU walks of life, and therefore we accept a certain amount of risk as part of our day-to-day living. Safety has been defined by some as acceptable risk. 

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The purpose of a risk management matrix is to (a) provide a logical framework for hazard analysis and risk assessment and (b) assist risk decision makers in arriving at their risk reduction and risk acceptance or declination conclusions. The implicit goal is to achieve acceptable risk levels. Several standards and guidelines now include the concepts of residual risk and acceptable or tolerable risk (e.g., ANSl/Bll TR3, ISO/IEC Guide 51, SEMI SIO—see references for full titles). 

Reduce the consequences This requires provision of defensive stabilization measures, amelioration of the behavior of the hazard, or relocation of the development to a more favorable location to achieve an acceptable or tolerable risk. 

The analysis of a risk—that is, its estimation—leads to the assessment of that risk and the decision-making processes of selecting the appropriate level of risk reduction. In most studies this is an iterative process of risk analysis and risk assessment until the risk is reduced to some specified level. The subjec t of acceptable or tolerable levels of risk that coiild be applied to decision making on risks is a complex subject which will not oe addressed in this section. 

Acceptable (barely tolerable) risks or doses used to classify low-hazard waste could be established based on a variety of considerations, consistent with the different approaches to risk management for radionuclides and hazardous chemicals described in Section 1.5.3. For noncarcinogenic hazardous chemicals, NCRP recommends that an acceptable dose should be set at a nominal threshold for deterministic responses in humans obtained as described in Section 1.5.5.3, or slightly below the threshold (e.g., by a factor of two or three) if an additional margin of safety is warranted. For... 

The risk index for any hazardous substance in Equation 1.1 or 1.2 (see Section 1.5.1) is calculated based on assumed exposure scenarios for hypothetical inadvertent intruders at near-surface waste disposal sites and a specified negligible risk or dose in the case of exempt waste or acceptable (barely tolerable) risk or dose in the case of low-hazard waste. Calculation of the risk index also requires consideration of the appropriate measure of risk (health-effect endpoint), especially for carcinogens, and the appropriate approaches to estimating the probability of a stochastic response per unit dose for carcinogens and the thresholds for deterministic responses for noncarcinogens. Given a calculated risk index for each hazardous substance in a particular waste, the waste then would be classified using Equation 1.3. 

Establishing an acceptable risk or dose. There also are a number of precedents for establishing an acceptable (barely tolerable) risk or dose of substances that cause stochastic responses for the purpose of classifying waste as low-hazard or high-hazard. For radionuclides, the annual dose limit for the public of 1 mSv currently recommended by ICRP (1991) and NCRP (1993a) and contained in current radiation protection standards (DOE, 1990 NRC, 1991) could be applied to hypothetical inadvertent intruders at licensed near-surface disposal facilities for low-hazard waste. This dose corresponds to an estimated lifetime fatal cancer risk of about 4 X 10 3. Alternatively, the limits on concentrations of radionuclides in radioactive waste that is generally acceptable for near-surface disposal,... 

NCRP notes that the modifying factor in the risk index should be applied independently of the requirement to achieve a negligible risk or dose for exempt waste or an acceptable (barely tolerable) risk or dose for nonexempt waste, in order to provide regulatory flexibility in classifying particular wastes. NCRP believes that such flexibility is highly desirable to promote cost-effective management and disposal of waste, provided it is applied in a transparent manner. 

Ren wick AG, Walker R, An analysis of the risk of exceeding the acceptable or tolerable daily intake, Regul. Toxicol. Pharmacol. 1993 18 463-480. 

Find the most cost-effective way to make the risk acceptable or tolerable... 

As has been noted here, some safety standards and guidelines issued in recent years include provisions for hazard analysis and risk assessment. That progression will continue, and its impact will be extensively felt. Those standards and guidelines reeognize that, even though hazard avoidance, elimination, and control measures are taken, there will always be residual risk, and that such risk should be acceptable—or tolerable, if you prefer. 

As a matter of principle, for an operation to proceed, its risks must be acceptable, or tolerable if you prefer. 

It should therefore be kept in mind that even if there is consensus on the valuation of risk expressed in a certain metric, such as Value-at-Risk (VaR), Fatal Accident Risk (FAR) and Potential Loss of Lives (PLL), the judgements about risk acceptance or tolerability could still be controversial. 

Once we estimate the risk, the next step in the risk management process is to evaluate its acceptability or tolerability. The basic principles, depicted in Fig. 10.2, are relatively straightforward. 

Once the stakeholder participation process is established and the activity is defined, the next step is analyzing the risks of that activity. The steps involved in risk analysis have already been discussed in some detail. The risk evaluation step follows the risk analysis step. Participation of the stakeholders is again critical in evaluating acceptability or tolerability of these risks. Guidelines established by others should only be used for demonstration purposes. 

In some organizations, risk levels that are acceptable or tolerable are defined in terms of degree of injury or damage to property. The following examples will give safety professionals a basis from which they can develop probability and severity levels, and thus risk levels, that are acceptable to the operations for which they give counsel ... 

There are a number of fundamental problems with process-based approaches to software safety management. While these do not appear to be resulting in safety-related software products of unacceptable quality, there is a difficulty in developing cogent arguments that the risks associated with safety-related software are acceptable or tolerable. 

Accept the risk This will usually require the risk to be considered to be within the acceptable or tolerable range. 

Avoid the risk This will entail avoiding the project, thus seeking an alternative site or form of development so that the revised risk becomes acceptable or tolerable. 

The perception of risk may be very different from person to person. Without a baseline method to assess risk, risk acceptance, or tolerance, your assessment and overall concerns... 

What RHT does not say is that the target (i.e., accepted or tolerated) level of accident risk by road users is immutably fixed and invariable under all circumstances although this misquotation can be found in many lay and even academic and professional communications. Instead, what RHT does say is that the target level of risk depends on the balance of the expected benefits and costs of choosing risky versus cautious behaviour alternatives. This balance varies as a function of the state of the economy, and especially as a consequence of countermeasures that are intended to increase a greater desire for safety. 

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