The fire safety operational booklet referred to in paragraph 2 shall include provisions
for preventing fire spread to the cargo area due to ignition of flammable
vapours and include procedures of cargo tank gas-purging and/or gas-freeing,
taking into account the provisions in paragraph 3.2.
3.2
Procedures for cargo tank purging and/or
gas-freeing
3.2.1 When the ship is provided with an inert
gas system, the cargo tanks shall first be purged in accordance with
the provisions of regulation 4.5.6 until
the concentration of hydrocarbon vapours in the cargo tanks has been
reduced to less than 2% by volume. Thereafter, gas-freeing may take
place at the cargo tank deck level.
3.2.2 When the ship is not provided with an inert
gas system, the operation shall be such that the flammable vapour
is discharged initially through:
-
.1 the vent outlets as specified in regulation 4.5.3.4;
-
.2 outlets at least 2 m above the cargo tank deck
level with a vertical efflux velocity of at least 30 m/s maintained
during the gas-freeing operation; or
-
.3 outlets at least 2 m above the cargo tank
deck level with a vertical efflux velocity of at least 20 m/s and
which are protected by suitable devices to prevent the passage of
flame.
3.2.3 The above outlets shall be located not less
than 10 m, measured horizontally, from the nearest air intakes and
openings to enclosed spaces containing a source of ignition and from
deck machinery, which may include anchor windlass and chain locker
openings, and equipment which may constitute an ignition hazard.
3.2.4 When the flammable vapour concentration
at the outlet has been reduced to 30% of the lower flammable limit,
gas-freeing may be continued at cargo tank deck level.
3.3
Operation of inert gas system
3.3.1 The inert gas system for tankers required in
accordance with regulation 4.5.5.1 shall be so operated as to render and maintain the
atmosphere of the cargo tanks non-flammable, except when such tanks are required to
be gas-free.
3.3.2 Notwithstanding the above, for chemical tankers,
the application of inert gas, may take place after the cargo tank has been loaded,
but before commencement of unloading and shall continue to be applied until that
cargo tank has been purged of all flammable vapours before gas-freeing. Only nitrogen
is acceptable as inert gas under this provision.
3.3.3 Notwithstanding regulation 1.2.2.2, the provisions
of this paragraph shall only apply to tankers constructed on or after 1 January 2016.
If the oxygen content of the inert gas exceeds 5% by volume, immediate action shall
be taken to improve the gas quality. Unless the quality of the gas improves, all
operations in those cargo tanks to which inert gas is being supplied shall be
suspended so as to avoid air being drawn into the cargo tanks, the gas regulating
valve, if fitted, shall be closed and the off-specification gas shall be vented to
atmosphere.
3.3.4 In the event that the inert gas system is unable
to meet the requirement in paragraph 16.3.3.1 and it has been assessed that it is
impractical to effect a repair, then cargo discharge and cleaning of those cargo
tanks requiring inerting shall only be resumed when suitable emergency procedures
have been followed, taking into account guidelines developed by the Organizationfootnote.