8.6 Cargo tank gas-freeing
Clasification Society 2024 - Version 9.40
Statutory Documents - IMO Publications and Documents - International Codes - IBC Code - International Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in BulkAmended by Resolution MEPC.225(64) - Chapter 8 Cargo tank venting and gas-freeing arrangements - 8.6 Cargo tank gas-freeing

8.6 Cargo tank gas-freeing

  8.6.1 The arrangements for gas-freeing cargo tanks used for cargoes other than those for which open venting is permitted shall be such as to minimize the hazards due to the dispersal of flammable or toxic vapours in the atmosphere and to flammable or toxic vapour mixtures in a cargo tank. Accordingly, gas-freeing operations shall be carried out such that vapour is initially discharged:

  • .1 through the vent outlets specified in 8.3.4 and 8.3.5; or

  • .2 through outlets at least 2 m above the cargo tank deck level with a vertical exit velocity of at least 30 m/s maintained during the gas-freeing operation; or

  • .3 through outlets at least 2 m above the cargo tank deck level with a vertical exit velocity of at least 20 m/s which are protected by suitable devices to prevent the passage of flame.

When the flammable vapour concentration at the outlets has been reduced to 30% of the lower flammable limit and, in the case of a toxic product, the vapour concentration does not present a significant health hazard, gas-freeing may thereafter be continued at cargo tank deck level.

  8.6.2 The outlets referred to in 8.6.1.2 and 8.6.1.3 may be fixed or portable pipes.

  8.6.3 In designing a gas-freeing system in conformity with 8.6.1, particularly in order to achieve the required exit velocities of 8.6.1.2 and 8.6.1.3, due consideration shall be given to the following:

  • .1 materials of construction of system;

  • .2 time to gas-free;

  • .3 flow characteristics of fans to be used;

  • .4 the pressure losses created by ducting, piping, cargo tank inlets and outlets;

  • .5 the pressure achievable in the fan driving medium (e.g. water or compressed air); and

  • .6 the densities of the cargo vapour/air mixtures for the range of cargoes to be carried.

Parent topic: Chapter 8 Cargo tank venting and gas-freeing arrangements
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