Qualitative Risk Analysis

Qualitative risk analysis is an essential part of risk management framework and risk assessment process in all organizations. Qualitative risk analysis is a management technique concerned with examining the probability of a risky event and the impact of the risk if it occurs. All risks have both probability and impact that characterizes the risk. Probability is the likelihood that a risk event will occur, and impact is the significance of the consequences of the risk event. The two primary functions of a qualitative risk analysis are risk identification and risk estimation. Qualitative risk analysis requires that the probability and consequences of the risks be evaluated using established qualitative-analysis methods and tools. In this chapter, the theoretical basis for qualitative risk analysis principles, typical qualitative methods, and experiences of their use are presented. In addition to that the overall systems engineering viewpoints to systematic risk assessment and the need for qualitative risk analysis methods in different safety engineering domains are discussed in this chapter. New digital technology increases the complexity of the systems and introduces new potential unexperienced causal factors. This implies that proactive analysis and control of system hazards is growing increasingly important. Qualitative risk analysis techniques, which have long been used in industries that use dangerous processes and for other hazardous systems, can identify the causes of accidents that have never occurred before. Qualitative risk analysis methods have certain strengths, for example, they are relatively quick and easy to set up; they allow risks to be considered very early in the system lifecycle; they provide the means to systematically and thoroughly examine a system, process, or procedure; and the simple risk matrix provides a rapid ranking of risks into different significance levels. Practical experiences have also shown that systematic analysis of system operations and system functions by using qualitative PHA, OHA, and HAZOP methods bring out a great deal of useful information that are not directly related to safety but do have links to system availability, system usability, and system reliability. On the other hand, qualitative risk analysis methods are said to be not comprehensive, neither do they provide detailed information on risks and how risks can best be prevented. Methods rely heavily on the expertise of the analysts who may find it difficult to be sufficiently objective. It is also argued that risk matrices should be used with caution. Risk management decisions cannot be based in principle only on mapping of ordered category ratings of severity and probability factors to recommendations for actions or priorities. Strengths, uncertainties, and limitations of the qualitative risk analysis methods and analysis techniques as well as experiences and criticism are discussed more in this chapter.