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2025 Hazard Mitigation Plan <br />Kittitas Gounty, Washington ffitffi#l <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 />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 />The assessment of hazard frequency is generally based on past hazard events in the area and <br />professionaljudgment 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. Extenillntensity 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.9., Saffir-Simpson, Enhanced Fujita, Modified <br />Mercalli). Extent/lntensity Factors are hazard-specific and are detailed in each hazard profile. Table 44 <br />outlines the extent/intensity factors used in the risk assessment calculations for this Plan. <br />Table 4-4. ExtenUlntensity Factor <br />3Significant hazard event is likely to occur annually <br />2Significant hazard event is likely to occur within 25 years. <br />1LowSignificant hazard event is likely to occur within 100 years <br />0UnlikelyThere is little to no probability of significant occurrence, or the recurrence <br />interval is greater than every 100 years. <br />ril ,iri t,rn <br />Probability Description Probability <br />Factor <br />Historical and/or probabilistic models/studies for this hazard indicate <br />the possibility of a high-intensity incident.3 <br />Historical and/or probabilistic models/studies for this hazard indicate <br />the possibility of a medium-intensity incident.2 <br />1LowHistorical and/or probabilistic models/studies for this hazard indicate <br />the possibility of a low-intensity incident. <br />0UnlikelyHistorical and/or probabilistic models/studies for this hazard indicate <br />the possibility of little to no intensity. <br />DescriptionProbability <br />r\'1i:i,i iiLrtii|lr <br />Extent <br />Factor <br />Chapter 4: Hazard ldentification and Risk Assessment 58