Risk level determination

Eight years after MACT is installed on a source, EPA must examine the risk levels remaining at the regulated facilities and determine whether additional controls are necessary to reduce unacceptable residual risk. 

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. 

Usually there is no opportunity to repeat the measurements to determine the experimental variance or standard deviation. This is the most common situation encountered in field measurements. Each measurement is carried out only once due to restricted resources, and because field-measured quantities are often unstable, repetition to determine the spread is not justified. In such cases prior knowledge gained in a laboratory with the same or a similar meter and measurement approach could be used. The second alternative is to rely on the specifications given by the instrument manufacturer, although instrumenr manufacturers do not normally specify the risk level related to the confidence limits they are giving. 

Where sufficient toxicologic information is available, we have derived minimal risk levels (MRLs) for inhalation and oral routes of entry at each duration of exposure (acute, intermediate, and chronic). These MRLs are not meant to support regulatory action but to acquaint health professionals with exposure levels at which adverse health effects are not expected to occur in humans. They should help physicians and public health officials determine the safety of a community living near a chemical emission, given the concentration of a contaminant in air or the estimated daily dose in water. MRLs are based largely on toxicological studies in animals and on reports of human occupational exposure. 

Quantitative risk assessment is now used extensively for determination of chemical and microbial risks in food. This concept helps to systematically and scientifically judge whether certain hazardous compounds may reach unacceptable risk levels when ingested. Quantitative risk assessment can support both quality design and quality assurance but, we discuss it from the assurance perspective. In the past decade, much attention has been paid to assessment of microbial risks due to then-typical differences as compared to chemical risks ... 

Problems posed by the determination of toxic risk levels... 

The quality of the determination of risk levels set by regulation depends on the quality of measurements of lethal concentrations and doses (LC and LD50). From safety data in Part Three it is seen that this quality is far from being reached. 

The only difficulty in this method (in addition to the calculations, which are easily carried out using computers) is the fact that it is impossible to analyse tables with values that are missing, so there is a need to choose substances for which there are a whole range of LC and LD values. Since this is impossible, three tables were used, which all have in common the L050 variables for rat and mouse, orally and by intraperitoneal means of penetration, so that the coherence of the three tables and a strong enough relationship between them could be ablished. The purpose was to determine, if, in the absence of one of the classification criteria set by regulation, it was possible to choose another available criterion to determine the risk level of toxicity. 

First note that the determination criteria for risk level and nature set by labour regulations are not respected. It should be R20/22. Our approach gives R20/21/22. 

The risk assessment has also concluded that a level of 200 mg/kg for lead in the soil will be a protective level for expected site exposures along with an excess cancer risk level for TCE-contaminated soil (56 pg/L). Based on investigations of activities at the site, the TCE-contaminated soil has not been determined to be a listed RCRA hazardous waste, as the cleaning solution records indicate the solution contained less than 10% TCE. However, the lead-contaminated soil is an RCRA hazardous waste by characteristic in this instance due to extraction procedure (EP) toxicity. None of the waste is believed to have been disposed at the site after November 19, 1980 (the effective date for most of the RCRA treatment, storage, and disposal requirements). 

Two assumptions about the surface have been made to determine the effect of natural attenuation on the contaminated groundwater. First, despite the fractured nature of the bedrock, it has been assumed that the subsurface is homogeneous so as to facilitate the evaluation. Second, the potential for reduction in TCE concentrations has been assessed using a hydrogeologic model in which the fact that the cap would reduce existing leachate production by 75% is taken into account. This model is assumed to predict that the concentration of TCE in the groundwater would be reduced to an excess cancer risk level of 28 pg/L in 60 yr and an excess cancer risk level of 5 pg/L, approximately equal to the MCL, in approximately 100 yr. 

For most chemicals, actual human toxicity data are not available or critical information on exposure is lacking, so toxicity data from studies conducted in laboratory animals are extrapolated to estimate the potential toxicity in humans. Such extrapolation requires experienced scientific judgment. The toxicity data from animal species most representative of humans in terms of pharmacodynamic and pharmacokinetic properties are used for determining AEGLs. If data are not available on the species that best represents humans, the data from the most sensitive animal species are used to set AEGLs. Uncertainty factors are commonly used when animal data are used to estimate minimal risk levels for humans. The magnitude of uncertainty factors depends on the quality of the animal data used to determine the no-observed-adverse-effect level (NOAEL) and the mode of action of the substance in question. When available, pharmocokinetic data on tissue doses are considered for interspecies extrapolation. 

In the petroleum industry, insurance agents will typically estimate the maximum losses a facility may suffer by performing a calculation of a potential vapor cloud explosion at the facility (where this is applicable). By examining the high loss explosion potentials, a maximum risk level can be determined and therefore insurance coverages that are necessary will be defined. 

Upgrade to the existing facility depends on the increase in blast capacity required. Level of blast protection is generally based on building category, function, risk level and blast loads. Structural assessment and cost evaluation are then made to determine the best alternative to use. 

Used to determine an intermediate Minimal Risk Level (MRL) of 0.01... 

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