SECTION 4: RISK ASSESSMENT
Table 4.5 – Priority Risk Index RISK ASSESSMENT CATEGORY
LEVEL
DEGREE OF RISK CRITERIA
INDEX WEIGHT
PROBABILITY What is the
UNLIKELY
LESS THAN 1% ANNUAL PROBABILITY
1
POSSIBLE
BETWEEN 1 & 10% ANNUAL PROBABILITY
2
likelihood of a hazard event occurring in a given year?
30%
BETWEEN 10 &100% ANNUAL PROBABILITY
LIKELY
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
SPATIAL EXTENT How large of an area could be impacted by a hazard event?
NEGLIGIBLE
LESS THAN 1% OF AREA AFFECTED
1
SMALL
BETWEEN 1 & 10% OF AREA AFFECTED
2
20%
MODERATE
BETWEEN 10 & 50% OF AREA AFFECTED
3
Are impacts localized or regional?
LARGE
BETWEEN 50 & 100% OF AREA AFFECTED
4
MORE THAN 24 HRS 12 TO 24 HRS
1
SELF DEFINED
WARNING TIME Is there usually some lead time
2
SELF DEFINED
10%
associated with the hazard event? Have warning measures been implemented?
6 TO 12 HRS
3
SELF DEFINED
LESS THAN 6 HRS
4
SELF DEFINED
LESS THAN 6 HRS
1
SELF DEFINED
DURATION How long does the
LESS THAN 24 HRS LESS THAN 1 WEEK MORE THAN 1 WEEK
2
SELF DEFINED
10%
hazard event usually last?
3
SELF DEFINED
4
SELF DEFINED
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)]
Wake County, NC Multi-Jurisdictional Hazard Mitigation Plan
WSP June 2024 Page 71
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