SECTION 4: RISK ASSESSMENT
Table 4.5 – Priority Risk Index
RISK ASSESSMENT CATEGORY
LEVEL
DEGREE OF RISK CRITERIA
INDEX
WEIGHT
UNLIKELY
LESS THAN 1% ANNUAL PROBABILITY
1
PROBABILITY What is the likelihood of a hazard event occurring in a given year?
POSSIBLE
BETWEEN 1 & 10% ANNUAL PROBABILITY
2
30%
LIKELY
BETWEEN 10 &100% ANNUAL PROBABILITY
3
HIGHLY LIKELY
100% ANNUAL PROBABILTY
4
VERY FEW INJURIES, IF ANY. ONLY MINOR PROPERTY DAMAGE & MINIMAL DISRUPTION ON QUALITY OF LIFE. TEMPORARY SHUTDOWN OF CRITICAL FACILITIES. MINOR INJURIES ONLY. MORE THAN 10% OF PROPERTY IN AFFECTED AREA DAMAGED OR DESTROYED. COMPLETE SHUTDOWN OF CRITICAL FACILITIES FOR > 1 DAY MULTIPLE DEATHS/INJURIES POSSIBLE. MORE THAN 25% OF PROPERTY IN AFFECTED AREA DAMAGED OR DESTROYED. COMPLETE SHUTDOWN OF CRITICAL FACILITIES FOR > 1 WEEK. HIGH NUMBER OF DEATHS/INJURIES POSSIBLE. MORE THAN 50% OF PROPERTY IN AFFECTED AREA DAMAGED OR DESTROYED. COMPLETE SHUTDOWN OF CRITICAL FACILITIES > 30 DAYS.
MINOR
1
IMPACT In terms of injuries, damage, or death, would you anticipate impacts to be minor, limited, critical, or catastrophic when a significant hazard event occurs?
LIMITED
2
30%
CRITICAL
3
4
CATASTROPHIC
NEGLIGIBLE
LESS THAN 1% OF AREA AFFECTED
1
SPATIAL EXTENT How large of an area could be impacted by a hazard event? Are impacts localized or regional? WARNING TIME Is there usually some lead time associated with the hazard event? Have warning measures been implemented?
SMALL
BETWEEN 1 & 10% OF AREA AFFECTED
2
20%
MODERATE
BETWEEN 10 & 50% OF AREA AFFECTED
3
LARGE
BETWEEN 50 & 100% OF AREA AFFECTED
4
1
MORE THAN 24 HRS
SELF DEFINED
2
12 TO 24 HRS
SELF DEFINED
10%
6 TO 12 HRS
SELF DEFINED
3
SELF DEFINED
4
LESS THAN 6 HRS
SELF DEFINED
1
LESS THAN 6 HRS
DURATION How long does the hazard event usually last?
SELF DEFINED
2
LESS THAN 24 HRS
10%
SELF DEFINED
3
LESS THAN 1 WEEK
SELF DEFINED
4
MORE THAN 1 WEEK
The sum of all five risk assessment categories equals the final PRI value, demonstrated in the equation below (the highest possible PRI value is 4.0).
PRI = [(PROBABILITY x .30) + (IMPACT x .30) + (SPATIAL EXTENT x .20) + (WARNING TIME x .10) + (DURATION x .10)]
The purpose of the PRI is to categorize and prioritize all potential hazards for the Wake County planning area as high, moderate, or low risk. The summary hazard classifications generated through the use of the PRI allows for the prioritization of those high and moderate hazard risks for mitigation planning purposes. Mitigation actions are not developed for hazards identified as low risk through this process.
Wake County Multi-Jurisdictional Hazard Mitigation Plan 2019
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