5.12.1 The entry of personnel to the cargo tank
should be carried out only under the close supervision of a responsible
ship's officer and in accordance with national rules and/or with the
normal industrial practice laid down in the International Safety
Guide for Oil Tankers and Terminals.footnote The
particular hazards encountered in tanks which have been previously
inerted and then gas-freed are outlined in 9.2.8, 9.3.3 and chapter
10 of that Guide.
5.12.2 Practical precautions to meet these hazards
include:
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.1 securing the inert gas branch line gas valves
and/or blanks in position or, if gas-freeing with the inert gas blower,
isolating the scrubber from the flue gases;
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.2 closing of any drain lines entering the tank
from the inert gas main;
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.3 securing relevant cargo line valves or controls
in the closed position;
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.4 keeping the inert gas deck pressure in the
remainder of the cargo tank system at a low positive pressure such
as 200 mm water gauge. This minimizes the possible leakage of inert
or hydrocarbon gas from other tanks through possible bulkhead cracks,
cargo lines, valves, etc.;
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.5 lowering clean sample lines well into the lower
regions of the tank in at least two locations. These locations should
be away from both the inlet and outlet openings used for gas-freeing.
After it has been ascertained that a true bottom sample is being obtained,
the following readings are required:
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.6 the use of breathing apparatus whenever there
is any doubt about the tank being gas-free, e.g. in tanks where it
is not possible to sample remote locations. (This practice should
be continued until all areas, including the bottom structure, have
been thoroughly checked);
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.7 continuously ventilating and regularly sampling
the tank atmosphere whenever personnel are in the tank;
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.8 carefully observing normal regulations for
tank entry.