5.12 Tank entry
Clasification Society 2024 - Version 9.40
Statutory Documents - IMO Publications and Documents - Specifications and Manuals - Inert Gas Systems - 5 Application to Cargo Tank Operation - 5.12 Tank entry

5.12 Tank entry

  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:

  • .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;

  • .2 closing of any drain lines entering the tank from the inert gas main;

  • .3 securing relevant cargo line valves or controls in the closed position;

  • .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.;

  • .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:

    • .5.1 21% on a portable oxygen analyser; and

    • .5.2 less than 1% of lower flammable limit on a combustible gas indicator;

  • .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);

  • .7 continuously ventilating and regularly sampling the tank atmosphere whenever personnel are in the tank;

  • .8 carefully observing normal regulations for tank entry.

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