Hazards system foundations

This Report presents the foundations and technical principles for development of a generally applicable and risk-based hazardous waste classification system. Recommendations on suitable approaches to establishing boundaries of different waste classes are discussed these boundaries could be expressed, for example, in terms of limits on concentrations of hazardous substances. However, a particular implementation of the proposed waste classification system in terms of quantifying the boundaries of different waste classes is not presented. 

Dose-Response Assessment. Determining the relationship between the dose of a hazardous substance and the probability of a specific response is called dose-response assessment.6 This aspect of risk assessment is needed to extrapolate from responses observed in experiments or incidents involving high doses to the much lower potential doses relevant to waste disposal and other routine exposure situations. Dose-response assessment is a major issue in establishing the foundations of a risk-based waste classification system, and it is discussed in detail in Section 3.2. 

Dose-Response Relationships. The primary objective of this study is to set forth the foundations of a risk-based waste classification system that applies to hazardous chemicals and radionuclides. Most aspects of the risk assessment process that provide the basis for establishing this system are conceptually the same for chemicals and radionuclides, although the specific data (e.g., solubilities) may differ. One important exception is the assumed relationship of the probability of a response to a unit dose of a substance that causes stochastic effects, which is called the dose-response relationship There are important conceptual differences in the way this relationship has been defined and used for hazardous chemicals and radionuclides, and these differences could pose a major impediment to development of a risk-based waste classification system that applies to both types of substances on a consistent basis. These differences are elucidated in the following section. 

Previous sections have presented technical and historical information on radiation and chemical risk assessment and on classification of radioactive and hazardous chemical wastes. This information provides important perspectives for establishing the foundations of a new hazardous waste classification system. Before establishing these foundations, it is useful to specify the attributes that an ideal waste classification system should possess. The following sections identify the desirable attributes of a waste classification system including that the system should be risk-based, it should allow for exemption of waste, and it should be comprehensive, consistent, intrinsic, comprehensible, quantitative, compatible with existing systems, and flexible. These attributes should be recognized as goals that are not all likely to be fully realized in a practical waste classification system. 

The waste classification system should be developed in recognition of the types of information that are available and likely to be obtainable, and it should be specified to maximize compatibility with available information consistent with maintaining the fundamental integrity of the system. Establishment of a risk-based waste classification system must begin with the existing classification systems and associated databases (e.g., toxicity of hazardous substances). These would be expanded and refined as needed. However, if the foundations of a risk-based waste classification system or its implementation involve radically new concepts or call for data that cannot feasibly be obtained, the effort will be for naught. A realistic waste classification system must use the existing base of concepts and data to achieve the desired result. 

Process of Implementing the Waste Classification System. Taken together, the framework for waste classification discussed in Section 6.2 and the risk index developed in Section 6.3 and this Section constitute the foundations of a comprehensive and risk-based hazardous waste classification system. Such a waste classification system could be established by regulatory authorities using the following general process ... 

An important issue in developing a risk-based hazardous waste classification system is the degree of conservatism in protecting public health that should be embodied in the foundations and framework of the system and its implementation. The specific issues are, first, the extent to which calculations of risk in the numerator of the risk index should deliberately overestimate expected risks that arise from disposal of hazardous waste and, second, the extent to which the... 

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. 

System engineering starts with first determining the goals of the system. Potential hazards to be avoided are then identified. From the goals and system hazards, a set of system functional and safety requirements and constraints are identified that set the foundation for design, operations, and management. Chapter 7 describes how to establish these fundamentals. 

There are other engineering factors that affect the fire and explosion hazard, e.g., engineering standards of the structural steel and foundations, process equipment, heat exchangers, feeding system, fan and blowers, storage vessels, electrical equipment, instruments, and fire protection and safety equipment. Considerable assistance in design also can be obtained from relevant codes of practice. The responsibility for safe operation rests with the manufacturers of equipment and products as required by national law (e.g.. Factories Act and Health and Safety at Work Act in the United Kingdom). 

In the analysis of system safety, the initial process begins with the development of the preliminary hazard list during the project or system concept phase. Although it is not always compiled in aU cases, an available PHL can become the working foundation for the development of the preliminary hazard analysis during the design phase of the project life cycle. 

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