Page 223 - International safety guide for oil tankers and terminals

SHIPBOARD OPERATIONS

11.3.4 Tank Atmospheres
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Tank atmospheres can be either of the following:
11.3.4.1 Inert
the fire triangle namely:ย์ฝกพาณิชย์นาวี
This is a condition where the tank atmosphere is known to be at
its lowest risk of explosion by virtue of the atmosphere being
maintained at all times non-flammable through the introduction of
inert gas and the resultant reduction of the overall oxygen content
in any part of any cargo tank to a level not exceeding 8% by
volume while under a positive pressure (see Section 7.1.5.1).

The requirements for the maintenance of an inert atmosphere and
precautions to be observed during washing are set out in Section
7.1.6.9 and provide the most certain level of control of an
atmosphere during tank washing operations.

In fire triangle terms, this method physically removes and
controls the ‘oxygen’ side of the fire triangle.

11.3.4.2 Non-Inert
For the purposes of this Chapter, a non-inert atmosphere is one in
which the oxygen content has not been confirmed to be less than
8% by volume.
ึ
In recognition that tank washing and gas freeing operations in
non-inert atmospheres are considered to present a likelihood of
งานห้องสมุด ศูน
increased risk, additional control measures are required to reduce
the risk of operations to as low as reasonably practicable
(ALARP). These control measures MUST address two sides of

‘Fuel’ and

‘Sources of ignition’.

11.3.5 Tank Washing

11.3.5.1 Washing in an Inert Atmosphere

To satisfy the control measures for washing in inert atmospheres
see Section 7.1.6.9.

During tank washing operations, measures must be taken to verify
that the atmosphere in the tank remains non-flammable (oxygen
content not to exceed 8% by volume) and at a positive pressure.

11.3.5.2 Washing in a Non-Inert Atmosphere
Non-inert cargo tank washing should only be undertaken when
both the source of ignition and the flammability of the tank
atmosphere are controlled. To achieve this, the following
precautions to control ‘sources of ignition’ and ‘fuel’ MUST be
taken for tank washing operations in a non-inert atmosphere
condition.

© ICS/OCIMF/IAPH 2006 189