Part VIII Emergency Procedures - TP 4295 E

Transport Publication TP 4295 E

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54. (1) In the event of total failure of the inert gas system to deliver the required quality and quantity of inert gas and maintain a positive pressure in the cargo and slop tanks, action must be taken immediately to prevent any air being drawn into the tank; all cargo tank operations should be stopped, the deck isolating valve closed, and the vent valve between it and the gas pressure regulating valve opened and immediate action taken to repair the inert gas system.

(2) In the case of tankers engaged in the carriage of crude oil it is essential that the cargo tanks be maintained in the inerted condition to avoid the hazard of pyrophoric iron sulphide ignition; if it is assessed that the tanks cannot be maintained in an inerted condition before the inert gas system can be repaired, an external supply of inert gas should be connected to the system through the arrangements required by the Fire Protection, Detection and Extinguishing Equipment Regulations, as soon as practicable, to avoid air being drawn into the cargo tanks.

(3) In the case of product carriers, if it is considered to be totally impracticable to effect a repair to enable the inert gas system to deliver the required quality and quantity of gas and maintain a positive pressure in the cargo tanks, cargo discharge and deballasting may only be resumed provided that either an external supply of inert gas is connected to the system through the arrangements required by the Fire Protection, Detection and Extinguishing Equipment Regulations, or the following precautions as given in subsections (4) through (8) are taken.

(4) In the case of Safety Convention tankers built on or after 1 September 1984 or new tankers, the venting system is checked to ensure that approved devices to prevent the passage of flame into cargo tanks are fitted and that these devices are in a satisfactory condition.

(5) In the case of Safety Convention tankers built before 1 September 1984 or existing Non Safety Convention tankers the flame screens are checked to ensure that they are in a satisfactory condition.

(6) The valves on the vent mast risers are opened.

(7) No free fall of water or slops is permitted.

(8) No dipping, ullaging, sampling or other equipment should be introduced into the tank unless essential for the safety of the operation; if such equipment is necessary, it should be introduced only after at least 30 minutes have elapsed since the injection of inert gas ceased; all metal components of equipment to be introduced into the tank should be securely earthed; this restriction should be applied until a period of five hours has elapsed since injection of inert gas has ceased.

(9) In the case of product carriers if it is essential to clean tanks following a failure of the inert gas system and inerted conditions as defined in the Fire Protection, Detection and Extinguishing Equipment Regulations cannot be maintained, tank cleaning should be carried out with an external supply of inert gas connected to the system; alternately, if an external supply of inert gas is not connected to the ship, the following precautions as given in subsections (10) through (19) should be taken, in addition to subsections (4) through (8).

(10) Tank washing should be carried out only on one tank at a time.

(11) The tank being washed should be isolated from other tanks and from any common venting system, or the inert gas main and maximum ventilation output should be concentrated on that tank both before and during the washing process; ventilation should provide, as far as possible, a free flow of air from one end of the tank to the other.

(12) The tank bottom should be flushed with water and stripped; the piping system including cargo pumps, cross-overs and discharge lines should also be flushed with water.

(13) Washing should not commence until tests have been made at various levels to establish that the vapour content in any part of the tank is below 10 per cent of the lower flammable limit.

(14) Testing of the tank atmosphere should continue during the washing process; if the vapour level rises to within 50 per cent of the lower flammable limit, washing should be discontinued until the vapour level has fallen to 20 per cent of the lower flammable limit or less.

(15) If washing machines with individual capacities exceeding 60 m3/hour are to be used, only one such machine shall be used at any one time on the ship; if portable machines are used, all hose connections should be made and bonding cables tested for continuity before the machines are introduced into the tank; bonding cables should not be disconnected until after the machines have been removed from the tank.

(16) The tank should be kept drained during washing; if build-up of wash water occurs, washing should be stopped until the water has been cleared.

(17) Only clean, cold sea water should be used; recirculating systems should not be used.

(18) Chemical additives should not be used.

(19) All deck openings should be kept closed during the washing process, except those necessary for washing and venting.

(20) During cargo operations in port, more stringent regulations of the port authorities shall take precedence over any of the foregoing emergency procedures.

(21) The attention of the ship’s master should be drawn to Regulation 11(c), Chapter I, of the 1978 SOLAS Protocol in the event of the inert gas system becoming inoperative.

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