Introduction - Extreme Events: A Physical Reconstruction and Risk Assessment - page 4

Policy
and
planning
decisions

Probability of
occurrence of
hazard

Measures of
vulnerability and
exposure

Risk assessment
report

Figure 1.1. Generalised sequence of process occurring in a risk assessment. In
reality there are many feedback loops between the steps outlined here.

(2003)notes that people individually and collectively decide what precautionary
measures will be undertaken and how warnings will be complied with so as to
ensure that the loss resulting from a hazard event is limited to an acceptable
level. If the perceived risk is a true reflection of the actual risk associated with a
particular hazard, then mitigation strategies, warning compliance and response
preparedness are likely to be appropriate and vulnerability can be minimised. If
risk perception is biased, the reverse is true and vulnerability may be increased.
The perception of risk, therefore, can often be the precursor to determining the
level of exposure to that risk, although it is true that perceptions can and do
change over time. So increasing awareness with time, due to education about or
experience with the hazard may result in the realisation that more elements are
exposed than previously thought. The level of exposure, therefore, is a function
of past and present perceptions of risk.
The total risk is often expressed as:

risk (total) = hazard × elements at risk × vulnerability

Often each of these components of the risk equation is determined separately
and in isolation from the other components. When this occurs it is typically a
function of the background and the training of those employed to undertake
the task. Forexample,itiscommontohaveaphysical scientist or engineer
determine the probability of occurrence of the natural hazard, whereas social
scientists are usually best trained to deal with vulnerability and exposure. The
two sometimes do not fully comprehend each other's assessments and will not
question the veracity of the methods used or the results obtained. The social
scientist, for example, may not feel comfortable reviewing the engineer's assess-
ment of the hazard and will accept, at face value, the results as being correct or
the bestthat can be obtained. The level of exposure is then assessed which in
turn influences the assessment of vulnerability and vice versa. A report is often
produced which becomes the basis for planning and policy decisions by various
levels of government. Hence, the engineer's assessment is critical to and under-
pins all subsequent stages of the risk assessment process. Figure 1.1 outlines this
process.