Chemicals acceptable risks

The Fatal Accident Rate (FAR) is tlie nmiiber of fatal accidents per 1,000 workers in a working lifetime (10 lir). A responsible chemical company typically displays a FAR equal to 2 for chemical process risks such as fires, tovic releases or spillage of corrosive chemicals. Identify potential problem areas tliat may develop for a company if acceptable FAR numbers are e.vceeded. 

Acceptable Risk. Once information is assembled concerning the characteristics of exposure and biologic effects, that information must be interpreted in terms of human safety standards. That interpretation requires that one establish a set of criteria representing acceptably safe conditions for human existence, bearing in mind that zero concentrations of environmental chemicals are unrealistic. 

The general public has great difficulty with the concept of acceptable risk. The major objection is due to the involuntary nature of acceptable risk. Chemical plant designers who specify the acceptable risk are assuming that these risks are satisfactory to the civilians living near the plant. Frequently these civilians are not aware that there is any risk at all. 

Risk assessment is the conventional tool for decision making on the acceptability of chemical use. It is based on predicted exposure levels, predicted no-effect levels of individual chemicals and politically defined degrees of acceptable risk. Each of these processes involves a series of value judgements and estimations. Risk assessment is therefore highly subjective. 

Risk characterization for non-threshold effects, e.g., for chemicals that are both genotoxic and carcinogenic, generally proceeds by comparing the acceptable risk level (Section 6.2.4) with the actual or estimated total daily intake. An alternative, new approach is the margin of exposure approach (Section 6.4). 

Excipient compatibility and stability studies rely on two underlying assumptions. One is that there is no change in reaction mechanism as temperature increases the second is that the excipient is also chemically stable under the conditions of test. However, if the reaction mechanism does change with temperature, it is likely the result will show a disproportionately greater breakdown than would be anticipated from lower temperature studies. Thus the risk is that an excipient is rejected that might in reality be perfectly suitable for the formulation. In many cases this is probably an acceptable risk. 

Acceptable risks or doses for radionuclides and chemical carcinogens also could be established based on considerations of unavoidable risks from natural background as noted previously, these lifetime risks are about 10 2. For example, an acceptable risk could be set at a value corresponding approximately to the geographical variability in the background risk, because people normally do not consider this variability in deciding where to live. 

A proper reconciliation of the radiation and chemical paradigms for risk management is important to the development of a comprehensive and risk-based hazardous waste classification system. In particular, the proposed waste classification system developed in Sections 6.2 and 6.3 of this Report is based fundamentally on the concept that an acceptable risk generally can be substantially greater than a negligible risk. This distinction is used to define different classes of waste that pose an increasing hazard. 

An essential consideration in developing a risk-based waste classification system is the levels of acceptable risk that should be assumed in classifying waste. Therefore, an important concern in developing a comprehensive waste classification system is the different approaches to management of stochastic risks that have been used for radionuclides and hazardous chemicals. 

The risk-based waste classification system developed in this Report is based fundamentally on the concepts of negligible (de minimis) and acceptable (barely tolerable) risks from exposure to radionuclides and hazardous chemicals, with the crucial distinction that acceptable risks generally can be considerably higher than negligible risks. Therefore, in implementing the waste classification system, decisions would need to be made by regulatory authorities about... 

In many respects, the foundations and framework of the proposed risk-based hazardous waste classification system and the recommended approaches to implementation are intended to be neutral in regard to the degree of conservatism in protecting public health. With respect to calculations of risk or dose in the numerator of the risk index, important examples include (1) the recommendation that best estimates (MLEs) of probability coefficients for stochastic responses should be used for all substances that cause stochastic responses in classifying waste, rather than upper bounds (UCLs) as normally used in risk assessments for chemicals that induce stochastic effects, and (2) the recommended approach to estimating threshold doses of substances that induce deterministic effects in humans based on lower confidence limits of benchmark doses obtained from studies in humans or animals. Similarly, NCRP believes that the allowable (negligible or acceptable) risks or doses in the denominator of the risk index should be consistent with values used in health protection of the public in other routine exposure situations. NCRP does not believe that the allowable risks or doses assumed for purposes of waste classification should include margins of safety that are not applied in other situations. 

This Section provides example applications of the recommended risk-based waste classification system to a variety of hazardous wastes to illustrate its implementation and potential ramifications. Disposal is the only disposition of waste considered in these examples. In Section 7.1.1, a general set of assumptions for assessing the appropriate classification of hazardous wastes is developed, including a variety of assumed exposure scenarios for inadvertent intruders at waste disposal sites and assumed negligible and acceptable risks or doses from exposure to radionuclides and hazardous chemicals. Subsequent sections apply the methodology to several example wastes. 

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. 

Okrent and Xing (1993) estimated the lifetime cancer risk to a future resident at a hazardous waste disposal site after loss of institutional control. The assumed exposure pathways involve consumption of contaminated fruits and vegetables, ingestion of contaminated soil, and dermal absorption. The slope factors for each chemical that induces stochastic effects were obtained from the IRIS (1988) database and, thus, represent upper bounds (UCLs). The exposure duration was assumed to be 70 y. Based on these assumptions, the estimated lifetime cancer risk was 0.3, due almost entirely to arsenic. If the risk were reduced by a factor of 10, based on the assumption that UCLs of slope factors for chemicals that induce stochastic effects should be reduced by this amount in evaluating waste for classification as low-hazard (see Section 7.1.7.1), the estimated risk would be reduced to 0.03. Either of these results is greater than the assumed limit on acceptable risk of 10 3 (see Table 7.1). Thus, based on this analysis, the waste would be classified as high-hazard in the absence of perpetual institutional control to preclude permanent occupancy of a disposal site. 

Identification of risk levels and margins of safety in comparisons with other commonly encountered chemicals do not finally solve the problem whether a particular chemical risk constitutes a socially acceptable risk. This must finally be determined in the social institutions mentioned earlier at the various political jurisdictions. Whether a risk will be socially acceptable depends not only on the level of risk, which we have dealt with here, but on the nature of the risk, on who assumes the risk, who receives the benefit, and one s personal philosophy of accepting any risk versus zero risk. 

Jeff is a talented Staff Engineer employed by a major chemical plant in West Virginia he has a solid background in Loss Prevention. Jeff Josecks article was written to spark interest and discussion of process safety in safety meetings. It is also very skillfully worded to spark the readers into thinking about acceptable risks and minimal risks. 

A.W. van der Widen, Acceptable Risk Assessments by Industry Lessons from Experience and Challenge for Future, 23rd Annual Chemical Control Conference - The EU Draft Chemical Control Regulations, Charles Simeons Conferences, London, UK, 2002. 

If the results of a preliminary risk assessment, using a Tier 1 approach, do not generate acceptable risk levels, an examination of the physico-chemical properties of the substance, as well as the toxicological database of the product, may yield a justification for a lower dermal absorption default. A weight-of-evidence approach should be used, e.g. both the physico-chemical information and the toxicological database should support the reduced default. 

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