Risk assessment combinational hazards

As discussed in the previous problem set, the four major steps in a health risk assessment are hazard identification, dose-response assessment, exposure assessment, and risk characterization. A health risk assessment initially involves the identification of human health effects attributed to exposure to a chemical, usually on a continuous basis. A dose-response assessment determines how different levels of exposure to a hazard or pollutant affect the likelihood or severity of the health effects. An exposure assessment determines the extent of human exposure. These are combined to provide a risk characterization value. 

Prioritize hazards and associated risks by potential impact. The risk assessment combines the impact of all hazards and risk, comparing them against defined criteria as to what is acceptable. 

A number of vendors offer software based hazard assessment tools that help determine the magnitude of the hazards involved. With this software, calculations can be made to reflect the hazard for various failures. Some risk ranking software combines hazard assessment with probabilities of occurrence so that the relative risk levels can be assessed. 

If there are specific data germane to the assumption of dose-additivity (e g., if two compounds arc present at the same site and it is known that the combination is five times more toxic than the sum of the toxicitics for the two compounds), then tire development of the hazard index should be modified accordingly. The reader can refer to the EPA (1986b) mi.xiure guidelines for discussion of a hazjird index equation that incorporates quantitative interaction data. If data on chemical interactions are available, but arc not adequate to support a quantitative assessment, note the information in the assumptions being documented for the risk assessment. 

Tlie reader should also note that tlie risk to people can be defined in terms of injury or fatality. The use of injuries as a basis of risk evaluation may be less disturbing tlian tlie use of fatalities. However, tliis introduces problems associated with degree of injury and comparability between different types of injuries. Further complications am arise in a risk assessment when dealing witli multiple hazards. For example, how are second-degree bums, fragment injuries, and injuries due to toxic gas e.xposure combined Even where only one type of effect (e.g., tlueshold to.xic exposure) is being evaluated, different durations of e.xposure can markedly affect tlie severity of injury. 

Fire safety in a particular scenario is improved by decreasing the corresponding level of fire risk or of fire hazard. Technical studies will, more commonly, address fire hazard assessment. Fire hazard is the result of a combination of several fire properties, including ignitability, flammability, flame spread, amount of heat released, rate of heat release, smoke obscuration and smoke toxicity. 

Table 3 describes the main parts of an environmental risk assessment (ERA) that are based on the two major elements characterisation of exposure and characterisation of effects [27, 51]. ERA uses a combination of exposure and effects data as a basis for assessing the likelihood and severity of adverse effects (risks) and feeds this into the decision-making process for managing risks. The process of assessing risk ranges from the simple calculation of hazard ratios to complex utilisation of probabilistic methods based on models and/or measured data sets. Setting of thresholds such as EQS and quality norms (QN) [27] relies primarily on... 

The terminology used varies considerably. Hazard identification and risk assessment are sometimes combined into a general category called hazard evaluation. Risk assessment is sometimes called hazard analysis. A risk assessment procedure that determines probabilities is frequently called probabilistic risk assessment (PRA), whereas a procedure that determines probability and consequences is called quantitative risk analysis (QRA). 

Hazard is commonly defined as the potential to cause harm . A hazard can be defined as aproperty or situation that in particular circumstances could lead to harm (Smith et al., 1988). Risk is a more difficult concept to define. The term risk is used in everyday language to mean chance of disaster . When used in the process of risk assessment it has specific definitions, the most commonly accepted being The combination of the probability, or frequency, of occurrence of a defined hazard and the magnitude of the consequences of the occurrence (Smith et al., 1988). 

In the fire risk assessment, it is important to reevaluate the risk once options for mitigation are determined. The amount of risk reduction should be calculated for each option or combination of options. Often, the results indicate that some options do not provide much, if any, risk reduction. The use of cost benefit analysis can help management in deciding which option to select. Facilities that depend exclusively on the local fire department for fire protection should complete a fire hazard analysis to determine the appropriate fire protection. 

The characterisation of health hazards of food contaminants, the assessment of the occurrence of undesirable compounds in food and the estimation of the dietary intake are key issues in the risk assessment. In 2000, the European Commission published a White Paper on Food Safety, which underlined the importance of ensuring the highest possible standards of food safety and proposed a new approach to achieve them. Recently, PFCs have gained increased scientific and socioeconomic interest as emerging environmental contaminants due to the unique combination of persistence, toxicity and environmental prevalence. Risk assessment of the dietary exposure to PFCs, however, is hampered by the lack of sufficient data about the occurrence of these contaminants in food. 

As described in detail in this book, the use of assessment factors is an established practice in chemical risk assessment to account for uncertainties inherent in the hazard (effects) assessment and consequently, inherent in the risk assessment. The use of assessment factors to address this uncertainty is part of the conventional approach that has developed over the years. According to the current risk assessment paradigm, the usual approach is simply to multiply these individual assessment factors in order to establish an overall composite numerical assessment factor (Section 5.10). An alternative to the traditional assessment factor approach is to combine estimates of the ranges that these factors may encompass through a probabilistic assessment this is essentially a variation of the standard paradigm. 

In general, calculation of the risk or dose from waste disposal in the numerator of the risk index in Equation 6.2 or 6.3 involves the risk assessment process discussed in Section 3.1.5.1. As summarized in Section 6.1.3, NCRP recommends that generic scenarios for exposure of hypothetical inadvertent intruders at waste disposal sites should be used in calculating risk or dose for purposes of waste classification. Implementation of models describing exposure scenarios for inadvertent intruders at waste disposal sites and their associated exposure pathways generally results in estimates of risk or dose per unit concentration of hazardous substances in waste. These results then are combined with the assumptions about allowable risk discussed in the previous section to obtain limits on concentrations of hazardous substances in exempt or low-hazard waste. 

The Sediment Quality Triad (SQT) is an effects-based conceptual approach that can be used to assess and determine the status of contaminated sediments based on biology (laboratory and/or in situ toxicity tests), chemistry (chemical identification and quantification), and ecology (community structure and/or function). It provides a means for comparing three different lines of evidence (LOE) and arriving at a weight of evidence (WOE) determination regarding the risk posed by contaminated sediments. Effectively, each LOE comprises an independent assessment of hazard combined and integrated, they provide an assessment of risk. 

Recently, some models have been derived to analyze the occurrence of interactive joint action in binary single-species toxicity experiments (Jonker 2003). Such detailed analysis models are well equipped to serve as null models for a precision analysis of experimental data, next to the generalized use of concentration addition and response addition as alternative null models. However, in our opinion these models are not applicable to quantitatively predict the combined toxicity of mixtures with a complexity that is prevalent in a contaminated environment, because the parameters of such models are typically not known. Recently a hazard index (Hertzberg and Teus-chler 2002) was developed for human risk assessment for exposure to multiple chemicals. Based on a weight-of-evidence approach, this index can be equipped with an option to adjust the index value for possible interactions between toxicants. It seems plausible that a comparable kind of technique could be applied in ecotoxicological risk assessments of mixtures for single species. However, at present, the widespread application of this approach is prevented by lack of available information. 

Although use of isolators or other effective engineering controls is the preferred method of handling highly potent compounds in solid form, this is not the only possible approach. We have found that use of traditional laboratory controls and a combination of high level of PPE in conjunction with rigorous administrative controls can provide adequate protection. Before considering the use of any of these solutions in a workplace, make sure workers are fully informed about hazard identification, risk assessment and control options. 

Up to this point we have been exclusively concerned with identifying hazards. We have not been concerned with asking whether the hazards present any significant risk, or prioritising them in any way (recall that the risk is a combination of the severity of the hazard and the probability of its occurrence). For much of the time it will be intuitively obvious whether measures ought to be taken to eliminate or deal with an identified hazard. However, on occasion the decision might not be clear-cut and some form of risk assessment will be needed. 

Overall, the major premise for our approach is a directional orientation toward risk reduction. The evaluation procedure used follows a four-step process which considers first Hazard Identification second, Hazard Evaluation third, Risk Evaluation and fourth, Risk Response. To avoid any misunderstanding of terms, the combined activities of the first three steps can be considered as what is commonly referred to as making a "Risk Assessment." The fourth step, Risk Response, necessarily must follow when the process is used to make practical decisions. 

In the stepwise process, the risk evaluation combines the results of the second step, hazard evaluation, with any information on actual exposure possibilities, including evaluating exposure sources, levels, frequencies, types and routes. The assessment effort involves interpreting the field verified data from the perspective of determining what the actual risk level to humans and the environment is in the real world circumstances posed by the activity being evaluated. 

---