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Safety and reliability are two important aspects of science and technology. They are highly related, and they complement each other, i.e. they provide each other with more information than could be obtained individually. When safety and reliability are performed in collaboration, better and more efficient products can be produced. In 1 this module, we focus on one important aspect of safety, i.e. risk assessment. This module will explain what risk assessments are, and how they are conducted.
Risk assessment
As you learned in the previous section, risk assessment is a key element in a safety analysis. As explained in Harms-Ringdahl (2001) (Harms-Ringdahl, L (2001) Safety Analysis: Principles and Practice in Occupational Safety, CRC Press.), the general aim of a risk assessment is to provide a basis for deciding whether a system is acceptable as it is, or whether changes are necessary. Before we start to discuss risk assessment, however, you should watch another online video that briefly explains what risk assessment is (Activity 1 (Page 2)) .
Risk assessment can be done quantitatively or qualitatively.
- Quantitative risk assessment: Quantitative risk assessment requires calculations of two components of risk: the magnitude of the consequence (impact) of occurrence, and the probability of occurrence.
- Qualitative risk assessments: Qualitative risk assessments are descriptive, rather than measurable as in quantitative risk assessment.
Quantitative assessments
In science and technology areas, particularly in occupational health and safety applications, risk assessments are usually done quantitatively, or by presenting quantitative results qualitatively. Under quantitative approach to risk assessment, risk is defined as the probability of a hazard resulting in an adverse event, multiplied by the severity of the event (i.e. risk estimation). The quantitative measure of risks can then be used to judge whether or not a hazard is acceptable (i.e. risk evaluation). Under the IEC 1995 standard, this procedure is called probabilistic safety analysis or probabilistic risk analysis (http://en.wikipedia.org/wiki/ Probabilistic_risk_assessment). Figure 1.1 will briefly explain the procedure of a safety analysis.
