CPG 201: THIRA/SPR Guide—3rd Edition THIRA Step 1
14
Factor #1: Likelihood of a Threat or Hazard Affecting a Community
For the purposes of the THIRA, “likelihood” is the chance of a given threat or hazard affecting a
community. Likelihood is important to consider because communities must allocate limited
resources strategically. A particular threat or hazard might be possible, but communities should
determine whether the likelihood of its occurrence is large enough to drive investment decisions.
Through the THIRA, communities
identify the threats and hazards that
are challenging enough to expose
their capability gaps, and are likely
enough that a community can
justify investing in the capabilities
necessary to manage those threats
and hazards.
The ability to predict the likelihood
of a specific incident varies greatly
across threats and hazards. Some
hazards, such as floods, have
mature prediction models that can
allow communities to calculate the
numerical probability of a specific
incident, such as 1 in 100 or 1 percent a year, with a moderate degree of accuracy. Other
incidents, such as terrorism, are more difficult to predict and communities may most easily
express them on a logarithmic scale, such as 1 in 1,000, or on an ordinal scale, such as low,
medium, and high. Regardless of how communities express the probability of a specific
incident, understanding the likelihood of their threats and hazards can help communities
understand capability requirements and prioritize investments.
Including estimates of probability in the THIRA is not necessary, but communities may do so if
they deem it appropriate. Communities can also consider additional sources for useful likelihood
and consequence information to inform their threat and hazard selections, such as hazard
mitigation plans. Regardless of whether probability is included in the THIRA process,
communities only consider those threats and hazards that could realistically occur.
Factor #2: The Impacts of a Threat or Hazard
The projected impacts of threats and hazards determine the level of capability that a community
will need to address those impacts. To understand their risks effectively, communities should
identify and select threats and hazards that have impacts that most challenge their communities,
and therefore their capabilities. When assessing impact, it is important to consider that different
incidents present different types of challenges. In some cases, the sheer magnitude of the
incident may be substantial. In other cases, there may be operational or coordination
complexities or economic and social challenges.
Communities may include as many threats or hazards in their THIRA as they desire but should,
at a minimum, include as many threats and hazards as needed to most challenge each of the 32
core capabilities.
Considering the Location of Threat and Hazard
Consequences
Although incidents may have wider regional or national
effects, communities completing the THIRA should
focus strictly on the consequences within their
community. In some cases, it may be useful to include
threats and hazards that occur in other locations if they
trigger local effects.
For Example:
An industrial accident at a chemical plant located in one
particular community could affect people in another
community who are downwind or downriver from the
accident.