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PART VIII
EMERGENCY PROCEDURES
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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