Screening level risk analysis

Qualitative techniques, consisting of techniques for primarily hazard identification, such as SLRA (screening level risk analysis), checklist, what-if, what-if/checklist, HAZDP (guide-word hazard and operabiUty study), and FMEiA (failure modes and effects analysis). 

As facilities become familiar with the screening level risk analysis method, they may start using other methods as well, with each method having its own advantages and disadvantages. 

Screening level risk analysis (SLRA) is a systematic screening process to identify hazards and prioritize risks for developing risk control measures. 

Screening analysis was conducted for different exposure pathways and chemicals of concern. Using a screening level cutoff of a one-in-a-million excess risk for a 70-year lifetime exposure for the maximally exposed individual (MEI), a set of carcinogenic chemicals was identified for further analysis. For noncarcinogens, MEI exposure levels were compared to health thresholds. If the MEI exposure exceeded the established health threshold, further analysis was done. 

The first tier is the scoping activity, which identifies concerns and issues that have potential risks. Further detailed studies are done if there are identified unacceptable risks. Related to the levels of analysis, system boundaries (Fig. 1), and risk expressions (Fig. 2), through which the scoping activity proceeds, there some questions to be asked. The second tier is screening, in which the data describing the dose-response relationships of... 

In most cases a three tier approach is adopted, as shown in Fig. II/4.2.3-1. Initially, a qualitative or semiquantitative approach is taken to assess the risk and screen it. When risks are in a high risk zone or there is the possibility of a major accident event, then quantitative risk assessments are carried out to prescribe necessary control measures. It is quite common that in many cases a combined approach is necessary to justify consequence analysis. Mostly, when a quantitative approach is undertaken, prior preliminary analysis is done. From the diagram it is seen that whenever all replies to the queries shown in the diagram after qualitative analysis are NO, then the action stops. If any reply is YES, then the next level of analysis is carried out. A similar approach is applicable for semiquantitative and quantitative analyses (Fig. II/4.2.3-1). 

Routine screening is only successful with a well-drawn up risk analysis and implementation of a clearly defined control strategy, which includes threshold levels appropriate to size, age and species of fish. 

Traditional microbial screening methods have insufficient sensitivities to meet new regulations and classical physicochemical techniques, such as chromatographic methods and mass spectrometry which are often precluded due to the level of experience, skills, and cost involved. Moreover, these methods require laborious extraction and clean up steps that increase analysis time and the risk of errors. 

In discussions with EPA, we have noted that the Mitre Model does not appear to provide much ability to discriminate between the relative levels of risks posed by different sites, nor does it provide a basis for management decisions once a ranked list has been gathered. On the other hand, it is clear — again based on our experience — that the model would be too expensive to use as a screening device at any level, if it were made much more sophisticated than it is now. For example, the collection and analysis of data on the groundwater route can cost more than 100,000. Louisiana has done rather extensive site investigations for most of the sites listed with EPA, and the investments of resources have been substantial. We believe that, because of the simplicity of the Mitre Model, this poses problems of comparability with other ranked sites, where much less information may have been available. 

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