Acceptable risk levels definitions

I believe that developing a distinct and numerically explicit definition of an acceptable risk level that is universally applicable is not possible. 

We should recognize that a universally applicable definition of an acceptable risk level cannot be attained, other than in broad general terms, because of the many variables in individual risk situations. 

The enterprise shall mitigate subsystem-level risks that were assessed to be critical to subsystem development during system definition, and shall assess and mitigate assembly risks associated with each subsystem. For critical subsystem/assembly risks, simulations, scale model tests, or prototype tests should be used to demonstrate mitigation to an acceptable risk level with respect to cost, schedule, and/or performance. The enterprise should assess component risks and prioritize critical risks based on the probability of occmrence and related consequences to cost, schedule, and/or performance. 

The concept of As Low as Reasonably Practicable (ALARP) was recognized as a valuable tool in determining acceptable risk levels. However, a word of caution was offered On occasion, achieving risk levels as low as reasonably practicable will not be acceptable. Prior to presenting the following definition, I said that a workable and sound definition of acceptable risk must encompass hazards, risks, probability, severity, and economics ... 

For the practice of safety to be recognized as a profession, it must have a sound theoretical and practical base that, if applied, will be effective in hazard avoidance, elimination, or control and achieving acceptable risk levels. This author believes that there is a generic base for the work of safety professionals that must be understood and applied if they are to be effective. But, safety professionals have not yet agreed on those fundamentals or on the definitions of related terms. As Grimaldi and Simonds (1989) wrote in Safety Management. 

In the past, three criteria for risk acceptance were developed (a) the personal acceptance of risks, (b) the social acceptance, and (c) the economic criterion. The personally accepted risk level is defined as the frequency of suffering a certain degree of injury as a result of an event, accepted by an individual. The social risk concerns the risks for the total population. Society looks at the total consequence of an event, including the number of casualties, material and economic damage, and the loss of immaterial [matters]. Generally, the consideration of social consequences in the case of safety problems is limited to the number of casualties as a result of an event. More often, the social consequence is considered the total material damage. This definition is more suitable for an economic optimization of the risk level to be... 

Conversely, if the supplier s Quality Management System is very well written and there is documented evidence that the supplier adheres to it, the definition of risk levels might be relaxed a bit in the Function Risk Assessment. If the supplier s own acceptance testing is well documented and thorough, the Validation Plan should document the intent to reference some of the supplier testing in lieu of internal tests. It is not necessary to specify exact tests to be used at this point that can wait until the test plans are being prepared later on. 

Some risk analysts use the term as low as reasonably practical (ALARP) for setting a value for acceptable risk. The basic idea behind this concept is that risk should be reduced to a level that is as low as possible without requiring excessive investment. Boundaries of risk that are definitely acceptable or definitely not acceptable are established as shown in Figure 1.16, which is an FN curve family. Between those boundaries, a balance between risk and benefit must be established. If a facility proposes to take a high level of risk, then the resulting benefit must be very high. 

Achieving understanding of the terms used in risk assessment matrices is vital for their use in a particular organization. For example, in actual practice, a variety of definitions are used of the terms establishing probability and severity levels, as in Table 15.1. Terms applicable to a discussion of acceptable risk are presented in the following definitions. 

In these definitions, tolerable as a term is less demanding endurable, but only fairly good, not so bad. To be acceptable, the risk level should be satisfactory and agreeable, in accord with the dictionary definition. 

Finally, as in general risk assessment, definition of a risk level that is acceptable. 20.1.3 CONCLUSIONS... 

Despite the importance of threats and probability of their occurrence and definition of the manner of risk taking, the basic element of risk management is always risk assessment. The identified threats are the subject to analyses, estimation of risk level as well as to assessment of risk acceptability. Estimation of risk level usually consist of probability and importance of threats and their effects. Organisation should determine on its own which level of operational risk is acceptable for organisation and which can t be treated as the acceptable one. 

Therefore, the question still remains as to the proper definition of safety. One possible improvement of the previously presented MIL-STD-882 definition might be that safety is a measure of the degree of freedom from risk in any environment (Leveson 1986). Hence, safety in a given system or process is not measured as much as is the level of risk associated with the operation of that system or process. This fundamental concept of acceptable risk is the very foimdation on which system safety has developed and is practiced today. 

ZlO-2005 tersely states its purpose in Section 1.2 as follows The primary purpose of this standard is to provide a management tool to reduce the risk of occupational injuries, illnesses, and fatalities. This question logically follows. What risk reduction level is to be achieved This chapter Establishes that achieving a zero risk level is unattainable Discusses the great variations in cultural and situational aspects of risk acceptance and Combines the elements of risk (probability and severity) with ALARP (as low as reasonably practicable) to arrive at a definition of acceptable risk, the operational goal. 

Thus, safety is achieved in the workplace if the workers are free from unacceptable risk. That risk level must be defined, at least in general terms. But note in the definition given above that tolerable risk is that risk which is accepted in a given context. In a workable definition of risk, as we found, the context in which the work is being done must be considered. 

This note follows the definition above The expression acceptable risk refers to the level at which further risk reduction will not result in significant reduction in risk or additional expenditure will not result in significant advantages of increased... 

All personnel involved in the risk assessment processes must understand the definitions used for occurrence probability and severity and for risk levels in the risk assessment matrix chosen. An example of a risk assessment matrix is shown in Chapter 6 under Acceptable Risk. It includes examples of ... 

Public chemical exposures, by definition, cause everyone to "consume" the same ambient exposure. What should that exposure level be Because the harms from chemical exposure are collectively consumed, the efficient level is that which equates the sum of the marginal harms among those exposed with the marginal benefits of firms thaf emif (Samuelson 1954). Emissions reductions should occur until the abatement costs equal the sum of fhe amounfs that exposed people would pay to avoid (or be willing to accept in compensation for exposure to) a similar known risk in a market setting (Viscusi 1989a Broome 1978). 

In 1982, federal agencies concurred with a recommendation to increase the lower limit on concentrations of long-lived, alpha-emitting transuranium radionuclides in transuranic waste from 0.4 to 4 kBq g 1 (Steindler, 1982). This change in the definition of transuranic waste was made in response to difficulties in routinely measuring levels of alpha activity near 0.4 kBq g 1 in bulk solid waste and analyses which indicated that risks to public health from shallow-land burial of transuranium radionuclides in concentrations up to 4 kBq g 1 should be acceptable. 

In addition, the reliance on generic scenarios for inadvertent intrusion in classifying waste cannot, by definition, represent site-specific risks. However, this is not a serious shortcoming because such scenarios have been used in establishing subclasses of low-level radioactive waste for disposal in near-surface facilities (NRC, 1982a). Furthermore, as emphasized in this Report, establishment of a risk-based waste classification system using particular exposure scenarios does not obviate the need to perform site-specific risk assessments for the purpose of establishing waste acceptance criteria at each disposal site. 

Given the qualitative definitions of the three waste classes, the boundaries of the waste classes would be quantified based on explicit descriptions of how the definitions are related to risk. The boundaries would be expressed in terms of limits on amounts (concentrations) of individual hazardous substances, with specified rules for how to classify waste that contains mixtures of hazardous substances, such as the sum-of-fractions rule for mixtures of substances that induce stochastic effects. Specifically, waste would be classified as exempt if the risk that arises from disposal in a municipal/industrial landfill for nonhazardous waste does not exceed negligible (de minimis) levels. Use of a negligible risk to quantify limits on concentrations of hazardous substances in exempt waste is appropriate because the waste would be managed in all respects as if it were nonhazardous. Nonexempt waste would be classified as low-hazard if the risk that arises from disposal in a dedicated near-surface facility for hazardous wastes does not exceed acceptable (barely tolerable) levels. An essential condition of the definitions of exempt and low-hazard waste is that an acceptable (barely tolerable) risk must be substantially greater than a negligible risk. Waste would be classified as high-hazard if it would pose an unacceptable (de manifestis) risk when placed in a dedicated near-surface facility for hazardous wastes. 

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