Residual risk concept

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). 

If the residual risk for a task or operation is never zero, for what risk level does one strive At best, we can say that the concept of designing and operating to attain risk levels as low as reasonably achievable or practicable should be applied to the situation being considered. 

The concepts inherent in the terms ALARA and ALARP serve as guidelines in determining whether a risk is acceptable, but cannot be used as absolutes in decision-making. It should be understood that in an exceptional situation, even though the risk level attained is as low as reasonably achievable or practicable, a decision will be made that the residual risk is not acceptable and that the operation should not proceed. 

Residual risk the concept of loss-of-life expectancy... 

In a nuclear facility, as in any industrial plant, risk assessment distinguishes between the potential hazards that might be encountered in the absence of any protective measures, and the residual risks that will still remain despite the measures taken. The problem lies in assessing the latter, since there is no way of ensuring that they have been completely eliminated. The concept of event probability and its associated consequences was rapidly incorporated into safety analysis procedures, by taking account of the fact that the probability of an accident must be inversely proportional to the severity of the potential consequences for the public and the environment. 

A key development in system safety is the ALARP principle that states that the residual risk of a system shall be as low as reasonably practicable (ALARP principle) and was codihed through the UK Health and Safety at Work Act of 1974. The concept asserts that safety-critical systems and operations should be safe as far as reasonably practicable without risks to health and safety. This is important because it forces the overt decision to balance the realized safety benehts to the actual costs to implement in other words, residual risks are tolerable and thus do not need further mitigations. 

The UK Health and Safety at Work Act 1974 defined the concept of as low as reasonable practicable (ALARP). The ALARP principle is based on reasonable practicability, which simply means that hazard controls are implemented to reduce residual risk to a reasonable level of practicality. For a risk to be considered ALARP, it must be demonstrated that the cost in reducing the residual risk further would be grossly disproportionate to the benefit gained. Therefore, a risk assessment is conducted, and a cost-benefit analysis performed to determine how far to carry the hazard control. Of course, the challenge is deciding what is practical (e.g., cost, effort, time) balanced with how much benefit of lower residual risk the hazard control brings. Unfortunately, there is no standard method to demonstrate that the hazard control trade-off will meet ALARP. However, some of the following have been successfully used ... 

The system safety process is really an easy concept to grasp. The overall purpose is to identify hazards, eliminate or control them, and mitigate the residual risks. The process should combine management oversight and engineering analyses to provide a comprehensive, systematic approach to managing the system risks. Figure 2.3 details this process. 

The resultant risk matrix can be used to provide and develop an action plan which may also be assigned numbers so that priorities can be identified. Risk matrices are often colour coded to provide a visual concept of whether or not the residual risk is tolerable or acceptable. 

This ADI calculation process is based on the assumption that humans are at least as sensitive as the most sensitive laboratory animal exposed to the most sensitive test. This concept is not based on any scientific evidence but is used as a precaution against the uncertainties inherent in the process of risk assessment. The ADI corresponds to the quantity of residues consumers can take each day throughout their lives without incurring any appreciable risk to their health and, as such, expresses the intention to keep the risk to public health so low as to be insignificant. Under this perspective, the setting of this value is therefore strongly influenced by the concept of risk management. 

Because all 2,3,7,8-substituted PCDDs and PCDFs, as well as the planar PCBs, elicit this type of Ah-receptor mediated responses, their toxicity can be expressed relative to that of the most potent congener, which is 2,3,7,8-tctrachlorodibenzo-p-dioxin (TCDD). This concept is known as the toxic equivalence factor (TEF) approach.84,13 The TEF concept can be used to classify each individual congener and, by an additive approach, assess the total risk of environmental or biological levels of PCDDs, PCDFs and planar PCBs. The predictive value of this approach, in particular when PCBs are included, appears to be species- as well as response-dependent.13 This is primarily due to the presence of other PCBs in environmental residues, which may act antagonistically. 

The purpose of this paper is to describe flie policies and procedures of dietary exposure analysis and risk assessment in these two portions of die world, to highlight their differences, and to demonstrate how they both aim for the same goal, a safe food supply. Unless otherwise noted, all references to exposure in this paper pertain to the intake of pesticide residues in food. Nomenclature in other parts of the world refers to dietary intake, but the general concept is the same, regardless of the terminology. Likewise, all references to risk and risk assessment pertain to the risk assessment with regard to dietary exposure to pesticide residues. 

The reader now has some of the basic concepts necessary to objectively assess the real risk of consuming fruits and vegetables contaminated with residue levels of pesticides. There are a few more tools needed before we can solve the puzzle. Prior to addressing the true toxicology of these chemicals, we should become familiar with the actual culprits. 

The reader should now feel comfortable that eating fruits and vegetables is good for you and that even if they contain the trace levels of pesticides documented in Chapter 3, the risk must be minimal. Now I will present you with the ultimate paradox. Up until this point in the book, we have completely focused on the theoretical hazards associated with artificial man-made chemicals in our food. Implied in many discussions of food safety, and especially chemical residues, is the concept that if the food is natural and not tainted with man-made chemicals, then it must be safe and healthy. This is deeply rooted in the nostalgic view of the benevolence of nature. 

The So or the S.C. are permitted concentrations for total residues of the animal drug in edible tissues of focxi-producing animals. They have been calculated from a NOEL in a toxicity study or from an extrapolated 1 in 1 million risk in the diet of animals which exhibited a carcinogenic response in lifetime feeding studies. The total residue concept was discussed earlier and comes from the definition of a residue. All residues that result from administering a feed additive or an animal drug to a food animal are considered as potentially toxic as the parent compound that was fed to laboratory animals unless additional studies are done to remove them from concern. 

The requirements for a river basin-wide sediment concept will be even more challenging than the actual Water Framework Directive. It will include inventories of interim depots within the catchment area (underground and surficial mining residues, river-dams, lock-reservoirs), integrated studies on hydromechanical, biological and geochemistry processes, risk assessments on sedimentary biocoenoses, and last -but not least - the development of decision tools for sustainable technical measures on a river basin scale, including sediment aspects. 

In contrast, the EU approach consists of computing a TMDI using MRL, not median residue concentrations CVMP criticized the JECFA approach for its intrinsic limitation to a chronic risk scenario and also for several technical reasons, including difficulties of using linear regression to estimate the tolerance limit of residue concentrations with its confidence interval and to the rather loose concept of good veterinary practice. (For further details, see Ref. 106. For further details on and a discussion of the USFDA approach, see Refs. 105 and 108.)... 

---