5.2.1 The basic principle for the evaluation criterion
should be "safety equivalence". This means that the alternative and/or
equivalent will be designed so that it will perform its intended safety
related function(s) in a manner that is equivalent to or better than
the prescriptive requirement it is deviating from. The evaluation
criterion used for the evaluation of the alternative/equivalent design
shall be specified either on basis of prescriptive requirements or
an equivalent, regulations compliant design. Therefore, the safety
level of the prescriptive requirement should be made explicit to enable
a comparison with the safety level of the alternative and/or equivalent
design.
5.2.2 Depending on the area to which the approval
of the alternative and or equivalent design is being sought, the evaluation
criteria could fall into one or more of the following categories:
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.1 life safety criteria – These criteria
address the survivability of passengers and crew and may represent
the effects of flooding, fire, etc.
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.2 damage to ship structure and related systems
– These criteria address the impact that a casualty might have
on a ship structure, mechanical systems, electrical systems, fire
protection systems, etc. These criteria may represent physical effects
of an accident.
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.3 damage to the environment – These criteria
address the impact of an accident on the atmosphere and the marine
environment.
5.2.3 The evaluation criterion can be also specified
by means of performance criteria characterizing the safety level of
IMO regulations. In that case the performance criterion should be
developed, taking into consideration the intent of the regulations
and related mandatory instruments (e.g. mandatory codes and standards),
if any.
5.2.4 The purpose of the analyses is to verify
that a design with reasonable confidence will perform its intended
safety related function(s) when necessary and in a manner equivalent
to or better than the prescriptive IMO requirements.
5.2.5 The analysis used to show that the alternative
design and arrangements provide the equivalent level of safety to
the prescriptive IMO requirements should follow an established approach
to safety design. This approach should be based on sound science and
engineering practice incorporating widely accepted methods, empirical
data, calculations, correlations and computer models as contained
in engineering textbooks and technical literature. The general process
of analysis is outlined in section 4 of these Guidelines.
5.2.6 For alternative design falling into areas
where no appropriate IMO regulations or other relevant industry standard
exist the evaluation criteria may be specified by means of risk acceptance
and agreed with Administration.
5.2.7 Risk analysis is the calculation of probabilities
and consequences for the event examined and the conversion of these
into a risk metric (i.e. a measurable value, risk acceptance criterion,
evaluation criterion, safety level, etc.) based on which decisions
may be taken.
5.2.8 This approach may address the risk to human
life, including injuries and ill health, and the risk to the environment.
Other types of risk could also be covered, as appropriate to the design
of the alternative and/or equivalency in question.
5.2.9 Different risk metrics for each type of
risks can be employed and typically the following types of evaluation
criteria are used:
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.1 individual and societal risk; and
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.2 risk to crew, passengers and people ashore,
as appropriate.
5.2.10 The above are criteria for total risk (e.g.
fatalities from fire, collision, structural damage, etc.) as opposed
to criteria for individual hazards or individual risks. For the risk
assessment of structural issues of ships, among others, it may be
necessary to develop acceptance criteria for individual failure modes
(limit states) of ships (e.g. failure due to fatigue of steel plates).
This may also be necessary when examining the satisfaction or not
of acceptance criteria for individual functional requirements relating
to the structure of ships, its global and local strength, etc. Such
risk evaluation criteria for individual hazards of ship structures
and individual failure modes have not been developed nor established
to date.
5.2.11 The risk acceptance criteria should be
preferably specified by IMO or by the Administration otherwise.