A system of preventing any explosion in the cargo tanks of a tanker by replacing the cargo, as it is pumped out, by an inert gas, often the exhaust of the ship's engine. Gas-freeing must be carried out subsequently if the worker has to enter the empty tanks.

The system capable of:

  • Reducing the oxygen content of the atmosphere in each tank to a level at which combustion cannot be support.
  • Maintaining the atmosphere in any part of any cargo tank with an oxygen content not Exceeding 8% by volume at a positive pressure.
  • Eliminating the entry of air.
  • Purging of empty cargo tanks of a hydrocarbon gas.

System Requirements For Classification Society

  1. Sufficient gas can be obtained from main or auxiliary boiler to ensure effective inerting of the tanks, in particular, the rate of production must be at least 125% of the maximum rated capacity of the cargo pumps.

  2. That the oxygen content of the gas does not exceed 5% by volume, thus automatic combustion control of the boilers becomes mandatory.

  3. At least two blowers are fitted.

  4. A scrubber is fitted.

  5. The system must be fitted with an automatically closing valve in the inert gas line in case of water failure. Two non-return devices must be fitted on the weather deck.

  6. The system must be fitted with a pressure-vacuum breaking device to operate at 0.235 bar pressure and 0.058 bar vacuum.

  7. Audible and visible alarms are to operate

    • when the oxygen content of the gas supplied reaches 8% by volume.

    • at high gas temperature.
    • at low gas pressure.
    • at loss of water pressure in the scrubber and/or deck seal.
    • in case of power supply failure to the control system.
  8. Blowers must stop automatically at high gas temperature and/or loss of water to the scrubber or deck seal.
  9. Fixed or portable oxygen analysers must be provided.

Related Terms


An endorsement issued by a flag state administration to a certificate of competency of a ship’s officer allowing service on dangerous cargo carriers such as oil tankers, chemical carriers, or gas carriers.
Depending on the position and degree of personal responsibility, the following types of evidence are determined: tankerman - minimal responsibility, assistant - personnel directly involved in cargo operations, responsible person - personnel directly responsible for cargo operations and compliance with safety measures during cargo handling.


Cargo such as oil, coal, ore, woodchips, etc. not shipped in bags or containers


A cargo ship engaged in the tramp trade.


A plan outlining the spaces available for fuel, cargo, ballast, fresh water, etc, with guides on weight and volume for spaces at various drafts and displacements


Vessel designed for a combination of passengers, and different types of cargo.


A device for hoisting and lowering heavy weights, cargo, stores, etc


Cushioning material placed among cargo to prevent their motion


Non-bulk cargo. The cargo may be of various kinds


A wood placed in bottom of ship to keep cargo dry


The act of loading and discharging a cargo ship.

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