Acceptable risk definitions

In summary, the proposal of an appropriate definition of the residue is not a process which follows simple and unambiguous rules in each case. The differences between residue definitions of some European MRLs and US tolerances illustrate the importance of harmonization. However, the great effort sometimes necessary to reach a suitable and accepted residue definition, which considers the needs of risk assessors (toxicologists) and the feasibility aspects of residue analysts, is clearly a vital prerequisite for any method development and validation. 

The link between the ecological/ecotoxicological risk assessment and the risk management frameworks is demonstrated. The ecological risk assessment consists of seven interactive elements (Fig. 17). The quantitative and descriptive science used to conduct ERA (Table 5) does not answer, in a direct way, the question of what should be done to manage the risk. Science determines adversity, but the public determines acceptability (Fig. 18). But acceptable risk is a highly subjective and relative term. It is time and space-specific and depends upon definitions of quality of life and robustness of the environment. 

While it is clear that some people will not accept a definition of safety that is relative, it appears that most people feel safe when they are convinced that risks to their well-being are sufficiently low, even if not completely absent. (There are some dramatic and important qualifications on this conclusion, as we shall see in the later section concerning people s perceptions of risk. While for the most part people accept that the condition of safety is not equivalent to the condition of being completely risk-free, most people do not perceive risk as simply a matter of probability, as do the experts. This intriguing and well-documented fact complicates greatly the public dialogue on matters of risk.)... 

These considerations lead to the most problematic part of definitions and interpretation of terms the acceptable risk, sometimes also called limit risk. A totally risk free activity, also referred to as zero risk, is feasible only if the activity is not exercised If it has been decided to go for a quantitative risk statement, this is unavoidably accompanied by the request for a scale to enable the assessment of the result. The definition of such a scale presents a subjective decision on the acceptability of risk, which splits the scale into the regions dangerous or hazardous and safe . The value for the limit risk has to be fixed in such a way that it takes into account the acceptability for the damage facing party and at the same time the tolerability from a third parties point of view. With this background it becomes obvious that the definition of a limit risk comes close to a philosophical task on the political field with societal impact. 

Criticisms have been put forth regarding the conservative nature of current risk assessment methodology. Some have criticized the development of toxicity factors (such as the cancer slope factors) or the definition of acceptable risk (1,2), while others find fault with methodology used to assess exposure (3). The focus of this chapter is to evaluate the methodology of assessing risk from exposure to arsenic (As) in soils. 

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. 

Other authors include concepts of both incident probability and severity of consequences in their definitions of risk. In Of Acceptable Risk Science and the Determination of Safety, Lowrance wrote that ... 

Safety was defined as the freedom from unacceptable risk. Conversely, safety may be defined as that state for which the risks are judged to be acceptable. These definitions imply a determination of risk, as well as a judgment of the acceptability of risk. Often, when the term acceptable risk is used, the response of the uninformed may be. How dare you suggest that some risk is acceptable. 

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. 

An alternate. For those who prefer to deal in terms of acceptable risk, the definition just given is reversible. Thus, acceptable risk is defined as that risk which is tolerated in a given context based on current values of society. 

Meanings variously given to the terms acceptable risk and tolerable risk present a semantics problem. For some people, the terms are synonyms for others, they have markedly different meanings. Dictionary definitions of acceptable and tolerable differ slightly. Two descriptions for each term follow. 

When commencing this chapter, one intent was to develop a definition of acceptable risk that was universally applicable in all risk situations—one... 

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. 

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. 

In recognition of the educational need those beliefs presented, I tried to develop a definition of acceptable risk that was precise, terse, and possibly numerical, which could be universally applicable to all risk situations. I failed. Bruce Main, president of design safety engineering, joined me in researching and authoring a paper titled... 

As we proceeded with our studies, we found that developing a distinct, perhaps statistical, universally applicable definition of acceptable risk that did not contain general and judgmentally interpretive terms is not possible. But, with a studied understanding of risk, and risk taking, and the concept of As Low as Reasonably Practicable (ALARP), I dare to offer a practical definition of acceptable risk that can be effectively applied when dealing with workplace hazards, risks, and deficiencies in safety and health management systems. 

A sound and workable definition of acceptable risk must encompass hazards, risks, probability, severity, and economic considerations. Also, in the following definition, it is made clear that a risk level as low as reasonably practicable must also be tolerable ... 

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... 

What happens when the experts disagree Balanced reporting, by definition, means that there are always two sides to every story (the risk is either safe or dangerous ). The greater the disagreement - and thus controversy - that can be engendered, the better. What is an acceptable risk, who decides, and by which criteria If it eventually proves unacceptable, who will be blamed ... 

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