Qualitative risk assessment level

Table 2.1 Level 1 qualitative risk-assessment matrix...

Sound quantitative data on incident probabilities are seldom available. My associates skilled in system safety, a field in which quantitative risk assessments are routine, are not overly pleased when I say that most quantitative risk assessments are really qualitative risk assessments because so many judgments have to be made in the process to decide on the probability levels to be selected. 

Qualitative Risk Assessment An examination of system risk based upon established criteria that allow the analyst to evaluate risk levels in relation to other risks or total system risk. 

The risk assessment can be processed in a qualitative or quantitative framework. The qualitative risk assessment will be based on methods, principles, or rules for assessing risk based on nonnumerical categories or levels. An example would be where the safety manager assigns categorization of risks as low, medium, or high based on known data or assumptions regarding the risk environment. 

Risk assessment, a synthesis of the preceding three steps, which aims to assess both qualitatively and quantitatively the risks induced by a chemical at a given or at different exposure levels. 

Numerous qualitative approaches to risk assessment have been employed. Some sample categorizations follow. Health risks may be divided into risk levels as provided below ... 

The carcinogenic potential of the profiled substance is qualitatively evaluated, when appropriate, using existing toxicokinetic, genotoxic, and carcinogenic data. ATSDR does not currently assess cancer potency or perform cancer risk assessments. Minimal risk levels (MRLs) for noncancer end points (if derived) and the end points from which they were derived are indicated and discussed. 

The dangerous properties of acute toxicity, irritation, corrosivity, sensitisation, repeated-dose toxicity and CMR are evaluated in terms of their potential toxic effects to workers, consumers and man exposed indirectly via the environment, based on the use for each stage in the lifecycle of the substance from which exposure can occur. Risk assessment is also required if there are reasonable grounds for concern for potential hazardous properties, e.g., from positive in vitro mutagenicity tests or structural alerts. The risk assessment involves comparing the estimated occupational or consumer exposure levels with the exposure levels at which no adverse effects are anticipated. This may be a quantitative risk assessment, based on the ratio between the two values, or a qualitative evaluation. The principles of human health risk assessment are covered in detail by Illing (a.30) and more briefly in Chapter 7 of (73). 

Cancer risk assessment is basically a two-step procedure, involving a qualitative assessment of how likely it is that a compound is a human carcinogen, and a quantitative assessment of the cancer risk that is likely to occur at given exposure levels and duration of exposure. 

The outputs from risk assessment will normally include information about the relationship between dose and risk and estimates of levels of doses and thus risks in the population. For contaminants that have a toxicological threshold the Provisional Tolerable Weekly Intake (PTWI) might be defined and the number of consumers who have the potential to exceed this level of intake quantified. If a PTWI cannot be established (such as for genotoxic carcinogens) then it may be possible to quantify the proportion of a population exposed to a given level of risk by using QRA methods. If QRA methods cannot be applied then a qualitative assessment can be made such as to reduce intake levels to as low as is reasonably practicable. In either case it is the function of risk management to identify an optimal course of action to minimise the risk to consumers. 

It is important that both the qualitative and quantitative characterization be clearly communicated to the risk manager. The qualitative characterization includes the quality of the database, along with strengths and weaknesses, for both health and exposure evaluations the relevance of the database to humans the assumptions and judgements that were made in the evaluation and the level of confidence in the overall characterization. The quantitative characterization also includes information on the range of effective exposure levels, dose-response estimates (including the uncertainty factors applied), and the population exposure estimates. Kimmel et al. (2006) reviewed many of the components of the risk characterization for reproductive and developmental effects and provided a comprehensive list of issues to be considered for each of the components of the risk assessment. 

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