Biomedical Engineering Reference
In-Depth Information
natural hazards. While it is possible to estimate
how often many natural disasters will occur (for
example, a structure located in the 100-year flood-
plain is considered to have a 1 percent chance of
being flooded in any given year), it is very diffi-
cult to quantify the likelihood of a terrorist attack
or technological disaster. Quantitative methods
to estimate these probabilities are being devel-
oped but have not yet been refined to the point
where they can be used to determine incident
probability on a facility-by-facility basis. There-
fore, the planning team must use a qualitative
approach based on threat and vulnerability consid-
erations to estimate the relative likelihood of an
attack or accident rather than the precise frequency.
Such an approach is necessarily subjective but can
be combined with quantitative estimates of cost-
effectiveness (the cost of an action compared to
the value of the lives and property it saves in a
worst-case scenario) to help illustrate the overall
risk reduction achieved by a particular mitigation
action.
Prioritize Mitigation Actions
When prioritizing natural hazard mitigation
actions, a benefit-cost analysis is generally
conducted for each proposed action. Several factors
are considered, including:
Cost(s) of the mitigation action;
•
Dollar value of risk reduction (i.e., loss of life,
structure, content, and function) each time the
hazard occurs (discussed in detail in
Under-
standing Your Risks: Identifying Hazards and
Estimating Losses
[FEMA 386-2]);
•
•
Frequency with which the benefits of the action
will be realized (i.e., frequency of hazard occur-
rence); and
•
Time value of money (i.e., the fact that bene-
fits and costs in the future are worth less than
benefits and costs today).
These factors are then combined by calculating the
net present value of aggregate future benefits and
costs over the life span of the action. For more
details, see
Using Benefit-Cost Analysis in Mitiga-
tion Planning
(FEMA 386-5).
It is possible to determine
fairly accurately
how effective mitigation efforts will be in
preventing damages from a given type of attack.
The performance of many security and miti-
gation actions can be modeled using estab-
lished engineering techniques. For example,
structural engineers can determine how a hard-
ening action will protect a building's envelope.
Naturally, the effectiveness of actions that rely
on personnel or complex hardware can be more
difficult to ascertain. For example, what is the
probability that a security guard will fall asleep
or that lightning will disable a perimeter sensor
system?
While many benefits can be achieved
through implementing mitigation actions, plan-
ners should be sensitive to potential nega-
tive impacts as well. For example, altering
traffic patterns may increase commute times
and distances, and reducing on-street parking
may impact retail activity. Such considerations
can be pivotal in determining the feasibility,
viability, and potential for success of mitigation
planning initiatives.
Three challenges arise when applying this
benefit-cost framework to terrorism and technolog-
ical disaster mitigation actions: (1) the probability
of an attack or frequency of the hazard occurrence
is not known; (2) the deterrence rate may not be
known; and (3) the lifespan of the action may be
difficult to quantify.
First, the frequency factor is much more
complex in the case of manmade hazards than for
Second, the deterrence or preventative value of
an action cannot be calculated if the number of
incidents it averts is not known. Deterrence in the
case of terrorism may also have a secondary impact
in that once a potential target is hardened, a terrorist
may turn to a less protected facility—changing the
likelihood of an attack for both targets.
