2.1 A DP-system consists of components and systems
acting together to achieve sufficiently reliable position keeping
capability. The necessary reliability is determined by the consequence
of a loss of position keeping capability. The larger the consequence,
the more reliable the DP-system should be.
To achieve this philosophy the requirements have been grouped
into three equipment classes. For each equipment class the associated
worst case failure should be defined as in 2.2 below.
The
equipment class of the vessel required for a particular operation
should be agreed between the owner of the vessel and the customer
based on a risk analysis of the consequence of a loss of position.
Else, the Administration or coastal State may decide the equipment
class for the particular operation.
2.2 The equipment classes are defined by their
worst case failure modes as follows:
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.1 For equipment class 1, loss of position may
occur in the event of a single fault.
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.2 For equipment class 2, a loss of position is
not to occur in the event of a single fault in any active component
or system. Normally static components will not be considered to fail
where adequate protection from damage is demonstrated, and reliability
is to the satisfaction of the Administration. Single failure criteria
include:
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.1 Any active component or system (generators,
thrusters, switchboards, remote controlled valves, etc.).
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.2 Any normally static component (cables, pipes,
manual valves, etc.) which is not properly documented with respect
to protection and reliability.
For equipment class
3, a single failure includes:
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.1 Items listed above for class 2, and any normally
static component is assumed to fail.
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.2 All components in any one watertight compartment,
from fire or flooding.
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.3 All components in any one fire sub-division,
from fire or flooding (for cables, see also 3.5.1).
2.3 For equipment classes 2 and 3, a single inadvertent
act should be considered as a single fault is such an act is reasonably
probable.
2.4 Based on the single failure definitions in 2.2 the worst case failure should be determined
and used as the criterion for the consequence analysis (see
3.4.2.4).
2.5 The Administration should assign the relevant
equipment class to a DP-vessel based on the criteria in 2.2 and state it in the Flag State Verification
and Acceptance Document (FSVAD) (see
5.2).
2.6 When a DP-vessel is assigned an equipment
class this means that the DP-vessel is suitable for all types of DP-operations
within the assigned and lower equipment classes.
2.7 It is a provision of the guidelines that the
DP-vessel is operated in such a way that the worst case failure, as
determined in 2.2, can occur at any
time without causing a significant loss of position.