The system shall be capable of :
- inerting empty cargo tanks including slop tanks by reducing the oxygen content of the atmosphere in each tank to a level at which combustion cannot be supported;
- maintaining the atmosphere in any part of any cargo tank or slop tank at an oxygen content not exceeding 8 per cent by volume and at a positive pressure at all times both in port and at sea except when it is necessary for such a tank to be gas free;
- eliminating the need for air to enter tank during normal operations except when it is necessary for such tank to be gas free;
- purging empty cargo tanks including slop tanks or hydrocarbon gas, so that subsequent gas freeing operations will at no time create a atmosphere within the tank.
(3)(a) The system shall be capable of delivering inert gas to the cargo tanks and stop tanks at a rate of at least 125 percent of the maximum rate of discharge capacity of the ship, expressed as a volume ;
(b) The system shall be capable of delivering merit gas with an oxygen content or not more than 5 per cent by volume in the inert gas supply main to the cargo tanks and stop tanks at any required rate of flow.
(4) The inert gas supply may be treated flue gas from the main or auxiliary boilers, from one or more separagraphte gas generators or other sources or from any combination thereof. Director General of Shipping may approve systems using inert gases other than true gas, provided he is satisfied that an equivalent standard of safety I achieved. Systems using stored carbon dioxide shall not be permitted unless the Chief Surveyor with the Govt. of India is satisfied that the risk of ignition from generation of state electricity by the system itself is minimized.
(5) Flue gas isolating valves shall be fitted in the inert gas supply means between the boiler uptakes and flue gas scrubber. These valves shall be provided with indicators to show whether they are open or shut, and precautions shall be taken to maintain them gas-tight and keep the seating clear of soot. Arrangements shall be made so that boiler soot blowers cannot be operated when the corresponding flue gas valves open.
(6)(a) A flue gas scrubber shall be fitted which will effectively cool the volume of gas specified in paragraph (3) of this Schedule and remove solids and sulphur combustion products. The cooling water arrangements shall be such that an adequate supply of water will always be available without interfering with any essential services on the ship. Provisions shall also be made for an alternative supply of cooling water;
(b) Filters or equivalent devices shall be fitted to minimize the amount of water carried over to the inert gas blowers;
(c) The scrubber shall be located aft of all cargo tanks, slop tanks, cargo pump rooms and cofferdams separagraphting these spaces from machinery spaces of Category A.
(7)(a) Atleast two blowers shall be fitted which together shall be capable of delivering to the cargo tanks and slop tanks, at least the volume of gas required by paragraph (3).
In a system provided with a gas generator, the Chief Surveyor with the Govt. of India may permit only one blower if that system is capable of delivering the total volume of gas required by paragraph (3) to the protected cargo tanks, provided that sufficient spares for the blower and its prime mover are carried on board to enable any failure of the blower and its prime mover to be rectified by the ship’s crew.
(b) Two fuel oil pumps shall be fitted to the inert gas generator, Chief Surveyor with the Govt. of India may permit only one fuel oil pump on condition that sufficient spares for the fuel oil pump and its prime mover are carried on board to enable any failure of the fuel oil pump and its prime mover to be rectified by the ship’s crew.
(c) The inert gas system be so designed that the maximum pressure which it can exert on any cargo tank will not exceed the test pressure of any cargo tank. Suitable shut-off arrangements shall be provided on the suction and discharge connections of each blower.
Arrangements shall be provided to enable the functioning of the inert gas plant to be stabilized before commencing cargo discharge. If the blowers are to be used for gas freeing, their inlets shall be provided with blanking arrangements.
(d) The blowers shall be located aft of all cargo tanks, cargo pump rooms and cofferdams separating these spaces from machinery spaces of Category A.
(8) (a) The design and location of scrubber and blowers with relevant piping and fittings shall be such as to prevent fire gas leakages into enclosed spaces.
(b) To permit safe maintenance, an additional water seal or other effective means of preventing flue gas leakage shall be fitted between the flue gas isolating valves and scrubber or incorporated in the gas entry to the scrubber.
(9)(a) A gas regulating valve shall be fitted in the inert gas supply main. This valve shall be automatically controlled to close as required. It shall also be capable of automatically regulating the flow of inert gas to the cargo tanks unless means are provided to automatically control the speed of the inert gas blowers required in paragraph (7) of this Schedule.
(b) The valve referred to in sub-paragraph (a) of this paragraph shall be located at the forward bulkhead of the most forward gas safe space through which the inert gas supply main passes.
(10)(a) At least two non-return devices, one of which shall be a water seal, shall be fitted in the inert gas supply main, in order to prevent the return of hydrocarbon vapour to machinery spaces uptakes or to any gas safe spaces under all normal conditions of trim; 1st and motion of the ship. They shall be located between the automatic valve required by paragraph (9) of this Schedule and the aftermost connection to any cargo tank or cargo pipeline.
(b) The devices referred to in this paragraph shall be located in the cargo area on deck.
(c) The water seal referred to in sub-paragraph (a) of this paragraph shall be capable of being supplied by two separagraphte pumps, each of which shall be capable of maintaining an adequate supply at all times.
(d) The arrangement of the seal and its associated provisions shall be such that it will prevent back-flow of hydrocarbon vapours and will ensure the proper functioning of the seal under operating conditions.
(e) Provision shall be made to ensure that the water seal is protected against freezing, in such a way that the integrity of the seal is not impaired by overheating.
(f) A water loop or other arrangement approved by Director General of Shipping shall also be fitted in all associated water supply and dry piping and all venting or pressure sensing piping leading to gas safe spaces. Means shall be provided to prevent such loops from being emptied by vacuum.
(g) The deck water seal and all loop arrangements shall be capable of preventing return of hydrocarbon vapours at a pressure equal to the test pressure of the cargo tanks.
(h) The second non-return device mentioned in sub-paragraph (a) of this paragraph shall be a non-return valve or equivalent capable of preventing the return of vapours or liquids or both fitted forward of the deck water seal required by sub-paragraph (a) of this paragraph. It shall be provided with either positive means of closure or an additional valve having such means of closure located forward of the non-return valve to isolate the deck water seal from the inert gas main to the cargo tanks and slop tanks.
(i) As an additional safeguard against the possible leakage of hydrocarbon liquids or vapour back from the deck main, means shall be provided to permit the section of the line between the valve having positive means of closure referred to in sub-paragraph (h) of this paragraph, and the valve referred to in paragraph (9) of this Schedule to be vented in a safe manner when the first of these valves is closed.
11(a) The inert gas main may be divided into two or more branches forward of the non-return devices required by paragraph (10).
(b)(i) The inert gas supply main shall be fitted with branch piping leading to each cargo tank and slop tank. Branch piping for inert gas shall be fitted with either stop valves or equivalent means of control for isolating each tank. Where stop valves are fitted they shall be provided with locking arrangements, which shall be under the control of a responsible ship’s officer.
(ii) In combination carriers, the arrangements to isolate the slop tanks containing oil or oil residues from other tanks shall consist of blank flanges which will remain in position at all times when cargoes other then oil are being carried except as provided for in the relevant section of the Guidelines on Inert Gas Systems.
(c) Means shall be provided to protect cargo tanks and stop tanks against effect of over pressure or vacuum caused by thermal variations when such tanks are isolated from the inert gas main.
(d) Piping systems shall be so designed as to prevent the accumulation of cargo or water in the pipelines under all normal conditions.
(12) The arrangements for the venting of all vapours displaced from the cargo tanks during loading or ballasting shall comply with rule 66 of the Merchant Shipping (Cargo Ship Construction and Survey) Rules, and shall consist of either one or more mast risers or a number of rigid velocity vents. The inert gas supply main may be used for such venting.
(13) One or more pressure-vacuum breaking devices shall be provided to prevent the cargo tanks from being subject to :
- a positive pressure in excess of the test pressure of the cargo tank if the cargo were to be loaded at the maximum rated capacity and all other outlets were left shut; and
- a negative pressure in excess of 700 milimetres water gauge if cargo were to be discharged at the maximum rated capacity of the cargo pumps and the inert gas blower were to fail. Such devices shall be installed on the inert gas main unless they are installed in the venting system required by rule 66 of the Merchant Shipping (Cargo Ship Construction and Survey) Rules 1988 or on individual cargo tanks.
(b) The location and design of the devices referred to in sub-para (a) of this para shall be in accordance with rule 66 of the Merchant Shipping (Cargo Ship Construction and Survey) Rules, 1988.