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2025 Hazard Mitigation Plan <br />Kittitas County, Washington <br /> <br /> <br />Chapter 4: Hazard Identification and Risk Assessment 58 <br />4.3.1. Probability of Occurrence <br />The probability of occurrence of a hazard is indicated by a probability factor based on the likelihood of <br />annual occurrence. Numerical probability factors were assigned as follows. <br /> <br />Table 4-3 outlines the probability of occurrence factors used in the risk assessment calculations for this <br />Plan. A significant hazard event is defined as any hazard occurrence that directly or indirectly damages <br />structures or infrastructure, impedes normal business operations, and/or is likely to cause serious or fatal <br />injuries. <br />Table 4-3. Probability of Occurrence <br />Probability Description Probability <br />Factor <br />High Significant hazard event is likely to occur annually. 3 <br />Medium Significant hazard event is likely to occur within 25 years. 2 <br />Low Significant hazard event is likely to occur within 100 years. 1 <br />Unlikely There is little to no probability of significant occurrence, or the recurrence <br />interval is greater than every 100 years. 0 <br /> <br />The assessment of hazard frequency is generally based on past hazard events in the area and <br />professional judgment of local subject matter experts. <br />4.3.2. Extent Factors <br />Extent was assessed in two (2) categories – extent/intensity potential and catastrophic probability of the <br />hazard. Table 4-4 and Table 4-5 outline the numerical extent factors used in the risk assessment <br />calculation for this Plan. <br />4.3.2.1. Extent/Intensity Factor <br />Extent is defined as the range of anticipated intensities of the identified hazards. This category is most <br />commonly expressed using various scientific scales (e.g., Saffir-Simpson, Enhanced Fujita, Modified <br />Mercalli). Extent/Intensity Factors are hazard-specific and are detailed in each hazard profile. Table 4-4 <br />outlines the extent/intensity factors used in the risk assessment calculations for this Plan. <br />Table 4-4. Extent/Intensity Factor <br />Probability Description Extent <br />Factor <br />High Historical and/or probabilistic models/studies for this hazard indicate <br />the possibility of a high-intensity incident. 3 <br />Medium Historical and/or probabilistic models/studies for this hazard indicate <br />the possibility of a medium-intensity incident. 2 <br />Low Historical and/or probabilistic models/studies for this hazard indicate <br />the possibility of a low-intensity incident. 1 <br />Unlikely Historical and/or probabilistic models/studies for this hazard indicate <br />the possibility of little to no intensity. 0