Identifying and Evaluating Impacts - Mining and the Environment: From Ore to Metal - page 447

Risk Assessment Matrix

By dei nition, risk is characterized in terms of the severity of consequences and likelihood
of occurrence. Combining the probability and the severity of those consequences yields
an estimation of risk in the form of a simple two-dimensional diagram as schematically
shown in Figure 9.13 . As both probability and severity increase, the risk becomes less and
less acceptable.
To apply the risk assessment matrix in practice, three measures are required: (1) rating
of risk likelihood; (3) rating of risk consequences; and (3) rating of risk acceptability. All
three measures are dei ned according to parameters relevant to a specii c risk situation.
Rating risk likelihood and consequences produces a risk assessment matrix as illustrated
in Figure 9.14 . For each hazard the risk assessment matrix provides a consistent basis for
communicating risks and for deciding whether a specii c risk is acceptable or whether it
is not. The risk assessment matrix should of course be interpreted with caution, recogniz-
ing the oversimplii cation that it will normally represent. Both components - probability
and consequences - are likely to be at best semi-quantitative and so each component will

Risk is characterized in terms of
the severity of consequences and
likelihood of occurrence.

FIGURE 9.13
Schematic Two-dimensional Risk
Diagram - Illustrating Risk Likelihood,
Risk Consequences and Risk
Acceptability

RISK CATEGORIZATION

Low High

RISK CONSEQUENCES

Low

Risk is Usually
Acceptable Risk

Acceptability
Boundary

Project is not
Acceptable as
Proposed

High

FIGURE 9.14
Schematic Risk Assessment Matrix

Decreasing
Acceptability

CONSEQUENCES

Moderate/
Marginal

Insignificant Critical Catastrophic

The risk ranking from 'minor' to 'severe'
depends on the specifi c risk situation.

Minor Minor Moderate High

Unlikely

Moderate High

Severe

Minor

Seldom

Moderate Moderate

Occasional High Severe

Will Occur/
High Certainty

Moderate Moderate Severe Severe