Mishap severity

Five examples of risk assessment matrices follow. First, an adaptation is shown in Table 7 of the Mishap risk categories and mishap acceptance levels as in the working draft of MIL-STD-882E, the Department of Defense Standard Practice For System Safety. A comment in Appendix A of 882E is pertinent here A mishap assessment matrix allows classification by mishap severity and mishap probability and assists in managing the decision-making to achieve the necessary risk elimination or reduction to an acceptable level. ... 

Element 3—risk assessment. For each identified hazard, the mishap severity and probability or frequency are estabhshed. A mishap risk assessment matrix is used... 

The mishap likelihood factor is the probability of the hazard components occurring and transforming into the mishap. The mishap severity factor is the overall consequence of the mishap, usually in terms of loss resulting from the mishap (i.e., the undesired outcome). Both probability and severity can be defined and assessed in either qualitative terms or quantitative terms. Time is factored into the risk concept through the probability calculation of a fault event, for example, Pfailure = 1.0 - e where T = exposure time and X = failure rate. 

Figure 2.37 presents the HRI matrix concept for establishing the level of potential mishap risk presented by a hazard. It can be seen from this figure that the HRI matrix concept essentially involves one matrix and three tables. The HRI matrix is the main component, which is based upon the combination of the hazard/mishap likelihood on one axis and hazard/mishap severity on the other axis. The hazard/mishap likelihood category is determined from the criteria stated in the Likelihood Table and the hazard/mishap severity category is determined from the criteria stated in the Severity Table. The Risk Level Table ranks each hazard into one of four risk levels (high, serious, medium, or low) based on the particular HRI matrix indices designated for the particular level. 

It is the assessed consequences of the worst credible mishap that could be caused by a specific hazard. Severity can be stated in various terms, such as death, injury, system loss, system damage, environmental damage, and dollar loss. It should be noted that mishap severity and hazard severity are really the same entity, just viewed from two different perspectives. 

See Hazard Risk, Mishap Risk, and Mishap Severity for additional related information. 

Severity is one parameter in the risk equation. Risk is the safety measure of a potential future event, stated in terms of event likelihood and event severity. Mishap severity is the expected severity that would result from the occurrence... 

Method 1 shows an example of quantitative risk characterization by probability and severity cost. In this example, the mishap probability and cost of a hazard must be determined. The hazard risk point is then plotted on the graph and is determined as acceptable or unacceptable based on where it falls in the predefined acceptance region. In this method, mishap cost represents a method for measuring mishap severity. The major concern with this method is that there is little gradation in the acceptance level. 

Develop procedures and training. Incorporate special procedures and special training to guide personnel in safe operations. Procedures may include the use of PPE. For hazards assigned catastrophic or critical mishap severity, avoid using this step as the only risk reduction method. 

The MIL-STD approach is to make decisions regarding resolution of identified hazards based on the assessment of the risk involved. It requires the identification of the risk category by combining the mishap severity with the mishap probability. In this case, mishap is the same as an accident. ... 

Mishap severity categories are defined to provide qualitative measures of the worst credible mishap (i.e. accident) resulting from personnel error environmental conditions design inadequacies procedural deficiencies or system, subsystem or component failure/malfunction as shown in Table B.13. 

Mishap risk An expression of the impact and possibility of a mishap in terms of potential mishap severity and probability of occurrence (MIL-STD-882D). 

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