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c) Values may be assigned numerically to weigh the relative importance of each level of severity and
probability. A composite assessment of risk, to assist in comparing risks, may then be derived by
multiplying the severity and probability values.
6.3.15 Having used a risk matrix to assign values to risks, a range of values may be assigned in order
to categorize risks as acceptable, undesirable or unacceptable. These terms are explained below:
• Acceptable means that no further action needs to be taken (unless the risk can be reduced further
at little cost or effort).
• Undesirable (or tolerable) means that the affected persons are prepared to live with the risk in
order to have certain benefits, in the understanding that the risk is being mitigated as best as
possible.
• Unacceptable means that operations under the current conditions must cease until the risk is
reduced to at least the Tolerable level.
Chapter 6. Risk Management 6-7
Table 6-1. Risk assessment matrix
SEVERITY OF CONSEQUENCES LIKELIHOOD OF OCCURRENCE
Aviation
definition Meaning Value
Qualitative
definition Meaning Value
Catastrophic Equipment destroyed.
Multiple deaths.
5 Frequent Likely to occur many
times
5
Hazardous A large reduction in
safety margins,
physical distress or a
workload such that the
operators cannot be
relied upon to perform
their tasks accurately or
completely. Serious
injury or death to a
number of people.
Major equipment
damage.
4 Occasional Likely to occur
sometimes
4
Major A significant reduction
in safety margins, a
reduction in the ability
of the operators to cope
with adverse operating
conditions as a result of
an increase in workload,
or as a result of
conditions impairing
their efficiency.
Serious incident.
Injury to persons.
3 Remote Unlikely, but possible
to occur
3
Minor Nuisance. Operating
limitations. Use of
emergency procedures.
Minor incident.
2 Improbable Very unlikely to occur 2
Negligible Little consequence 1 Extremely
improbable
Almost inconceivable
that the event will
occur
1
6-8 Safety Management Manual (SMM)
6.3.16 A less numeric approach to determining the acceptability of particular risks includes
consideration of such factors as:
a) Managerial. Is the risk consistent with the organization’s safety policy and standards?
b) Affordability. Does the nature of the risk defy cost-effective resolution?
c) Legal. Is the risk in conformance with current regulatory standards and enforcement capabilities?
d) Cultural. How will the organization’s personnel and other stakeholders view this risk?
e) Market. Will the organization’s competitiveness and well-being vis-à-vis other organizations be
compromised by not reducing or eliminating this risk?
f) Political. Will there be a political price to pay for not reducing or eliminating this risk?
g) Public. How influential will the media or special interest groups be in affecting public opinion
regarding this risk?
6.4 RISK MITIGATION
6.4.1 Where risk is concerned, there is no such thing as absolute safety. Risks have to be managed to
a level “as low as reasonably practicable” (ALARP). This means that the risk must be balanced against the
time, cost and difficulty of taking measures to reduce or eliminate the risk.
6.4.2 When the acceptability of the risk has been found to be Undesirable or Unacceptable, control
measures need to be introduced — the higher the risk, the greater the urgency. The level of risk can be
lowered by reducing the severity of the potential consequences, by reducing the likelihood of occurrence or
by reducing the exposure to that risk.
6.4.3 The optimum solution will vary depending on the local circumstances and exigencies. In
formulating meaningful safety action, an understanding of the adequacy of existing defences is required.
Defence analysis
6.4.4 A major component of any safety system is the defences put in place to protect people, property
or the environment. These defences can be used to:
a) reduce the probability of unwanted events occurring; and
b) reduce the severity of the consequences associated with any unwanted events.
6.4.5 Defences can be categorized into two types, namely:
a) Physical defences. These include objects that discourage or prevent inappropriate action, or that
mitigate the consequences of events (for example, squat switches, switch covers, firewalls, survival
equipment, warnings and alarms).
Chapter 6. Risk Management 6-9
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