Qualitative Risk Levels

There are no restrictions or rules with respect to the terms used to establish qualitative risk levels. But a matrix, as a minimum, should illustrate probability and severity categories and risk gradings. Tables 7-11 show a general acceptance of a group of terms for incident probability and severity, and for risk categories. However, I repeat Safety professionals should draft matrices with which they are comfortable. Since risk assessment matrices are valuable communication tools, the terms used in them must be agreed on and the education time necessary to achieve an understanding of them must be allocated. 

The higher the qualitative risk level associated with the trigger event, the more likely that at least one extremely critical PSSR item will present itself as an item worthy of review. 

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. 

Their value does not refer to a real degree of the risk level variation. Therefore a substance in NFPA code 4 cannot be considered as presenting a risk that is twice as high as of a code 2 substence. This indicates the limits of physical factors, which are only a qualitative variable masked by an arbitrary increase of modalities that nevertheless improve the accuracy of classification. 

These criteria can be used to put forward a hypothesis on the potential toxicity risk level of a substance, which is not listed in labour regulations. The other criteria are either qualitative or take into account biological tests that go beyond the sphere of non-medical staff. It can be interesting to compare LC and LD50 data with clauses concerned with risk offered by the regulations and that appear in our tables. Here are a few examples of common substances, for which there is better information than for the others. 

Finally, an attempt will be made to show how the identified qualitative risk can be quantified to adapt the level of constraint of the operating modes. 

The estimated impact is then compared to hazard acceptance criteria to determine whether the consequences are tolerable without additional loss prevention and mitigation measures. If the identified consequences are not tolerable, the next step is to estimate the ffequency/probability of occurrence of the identified failure modes leading to loss of containment. For simple cases, frequency estimates are combined with consequences to yield a qualitative estimate of risk. For complex cases, fault tree analysis is used to estimate the frequency of the event leading to the hazard. These estimates are then combined with the consequences to yield a measure of risk. The calculated risk level is compared to a risk acceptance criterion to determine if mitigation is required for further risk reduction. 

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