Master Plan Nashua Fire Rescue, NH
Prioritizing Risk
Nashua used the following process to identify risks within the community.
1. Identification of Hazards: For each hazard type, the hazard location within the city, extent, and
impact are noted within the Hazard Mitigation Plan.
2. Description of Previous Hazards: The first step in determining the probability of future hazard
events in the City of Nashua was to examine the location, extent, and impact of previous hazards.
3. Probability of Future Hazard Events: After documenting the occurrence of previous hazard events
in the City of Nashua and the surrounding region, the Resilient Nashua Initiative stakeholders used
this information to calculate the annual probability of these events occurring in the future.
a. The first step was to determine how many times a particular hazard had occurred in a given
number of years. The year range is based upon the most detailed database being used for
the assessment. Because of this, there may be anumber of significant hazard event outliers,
primarily before 1960, that are not included in the probability calculation due to limited
historical data. The number of occurrences was then divided by the number of years to
determine the average number of events per year. For example, if history shows that a
particular hazard typically occurs 1 time every 4 years, the average number of events per year
is 0.25. The average number of events per year was calculated twice for each hazard. First,
the average number of events per year was calculated since the first recorded historical
occurrence of the event.
b. Second, the average number of events per year was calculated based on occurrences since
2000 (up to 2016) to reflect potential recent changes in hazard event occurrence rates.
c. Finally, the estimated probability of one or more hazard events in any year was calculated
using the Poisson Distribution.** For the Poisson Distribution, ) is the average number of
events per year and X is 1 (the number of years to be evaluated for probability). The
calculation looked at the greater to or equal likelihood of occurrence.
4. Critical Faculties and Their Vulnerabilities: The next step in determining the City’s overall
vulnerability was to inventory Nashua’s community assets and determine what assets would be
affected by each type of hazard event. The Resilient Nashua Initiative stakeholders began by
reviewing the City of Nashua Land Use Code to provide information on where and how the City builds
and to identify the corridors where critical facilities would likely be located. The stakeholders then
identified the broad categories of important assets within the City, including critical facilities
essential to health and welfare; vulnerable populations, such as children and the elderly; economic
assets and major employers; areas of high-density residential and commercial development; and
historical, cultural, and natural resources.
5. Vulnerability by Hazard: Finally, Nashua’s vulnerability to each hazard was identified and
categorized.
21 https://homepage.divms.uiowa. edu/~mbognar/applets/pois. html.
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