Section 15 Use of Cargo as Fuel

1501 General

1. Methane (CNG) may be utilized in machinery spaces of category A and in such spaces may be utilized only in boilers, inert gas generators, internal combustion engines and gas turbines.

2. These provisions do not preclude the use of gas fuel for auxiliary services in other locations, pro-

vided that such Society.

other services and locations are to be subject to special consideration by the

1502. Arrangement

1. Spaces in which

of machinery spaces of category A

gas fuel is utilized are to be fitted with a mechanical ventilation system and are

to be arranged in such a way as to prevent the formation of dead spaces. Such ventilation is to be particularly effective in the vicinity of electrical equipment and machinery or of other equipment and machinery which may generate sparks. Such a ventilation system is to be separate from those intended for other spaces.

2. Gas detectors are to be fitted in these spaces, particularly in the zones where air circulation is reduced. The gas detection system is to comply with the requirements of Sec 13.

3. Electrical equipment located in the double wall pipe or duct specified in 1503. 1 are to be of the intrinsically safe type.

1503. Gas fuel supply

1. Gas fuel piping is not to pass through accommodation spaces, service spaces, or control stations.

Gas fuel piping may pass through or extend into other spaces provided they fulfil one of the fol-

lowing:

(1) the gas fuel piping is to be a double wall piping system with the gas fuel contained in the in- ner pipe. The space between the concentric pipes is to be pressurized with inert gas at a pres- sure greater than the gas fuel pressure. Suitable alarms are to be provided to indicate a loss of inert gas pressure between the pipes; or

(2) the gas fuel piping is to be installed within a ventilated pipe or duct. The air space between the gas fuel piping and inner wall of this pipe or duct are to be equipped with mechanical ex- haust ventilation having a capacity of at least 30 air changes per hour. The ventilation system is to be arranged to maintain a pressure less than the atmospheric pressure. The fan motors are to be placed outside the ventilated pipe or duct. The ventilation outlets are to be placed in a position where no flammable gas-air mixture may be ignited. The ventilation is always to be in operation when there is gas fuel in the piping. Continuous gas detection is to be provided to indicate leaks and to shut down the gas fuel supply to the machinery space in accordance with Par 10. The master gas fuel valve required by Par 7 is to close automatically, if the required air flow is not established and maintained by the exhaust ventilation system.

2. If a gas leak occurs, the gas fuel supply is not to be restored until the leak has been found and repaired. Instructions to this effect are to be placed in a prominent position in the machinery spaces.

3. The double wall piping system or the ventilated pipe or duct provided for the gas fuel piping is to terminate at the ventilation hood or casing required by Par 4.

4. A ventilation hood or casing is to be provided for the areas occupied by flanges, valves, etc., and for the gas fuel piping, at the gas fuel utilization units, such as boilers, diesel engines or gas turbines. If this ventilation hood or casing is not served by the exhaust ventilation fan serving the ventilated pipe or duct as specified in Par 1 (2), then it is to be equipped with an exhaust ven- tilation system and continuous gas detection are to be provided to indicate leaks and to shut down the gas fuel supply to the machinery space in accordance with Par 10. The master gas fuel valve required by Par 7 is to be closed automatically if the required air flow is not established and maintained by the exhaust ventilation system. The ventilation hood or casing is to be installed or mounted to permit the ventilating air to sweep across the gas utilization unit and be exhausted at the top of the ventilation hood or casing.

5. The ventilation inlet and discharge for the required ventilation systems are to be respectively from and to a safe location.

6. Each gas utilization unit are to be provided with a set of three automatic valves. Two of these valves are to be in series in the gas fuel pipe to the consuming equipment. The third valve is to be in a pipe that vents, to a safe location in the open air, that portion of the gas fuel piping that is between the two valves in series. These valves are to be so arranged that failure of the neces- sary forced draught, loss of flame on boiler burners, abnormal pressure in the gas fuel supply line, or failure of the valve control actuating medium will cause the two gas fuel valves which are in series to close automatically and the vent valve to open automatically. Alternatively, the function of one of the valves in series and the vent valve can be incorporated into one valve body so arranged that, when one of the above conditions occurs, flow to the gas utilization unit will be blocked and the vent opened. The three shut-off valves are to be arranged for manual reset.

7. A master gas fuel valve that can be closed from within the machinery space is to be provided within the cargo area. The valve is to be arranged so as to close automatically if leakage of gas is detected, or loss of ventilation for the duct or casing or loss of pressurization of the double wall gas fuel piping occurs.

8. Gas fuel piping in machinery spaces is to comply with 502. to 505. as far as found applicable.

The piping is to, as far as practicable, have welded joints. Those parts of the gas fuel piping, which are not enclosed in a ventilated pipe or duct according to Par 1 and are on the open deck outside the cargo area are to have full penetration butt-welded joints and are to be fully ra- dio-

graphed.

9. Provision is to be made for inerting and gas-freeing that portion of the gas fuel piping system lo- cated in the machinery space.

10. Gas detection systems provided in accordance with the requirements of Pars 1 and 4 is to com- ply with 1306. 2 and 1306. 4 through 1306. 9 as applicable; they are to activate the alarm at 30

% of the lower flammable limit and shut down the master gas fuel valve referred to in Par 7 be-

fore the gas concentration reaches 60 % of the lower flammable limit.

1504. Gas make-up plant and related storage tanks

1. All equipment (heaters, fuel gas handling equipment, filters, etc.) for making up the gas for its use as fuel, and the related storage tanks are to be located in the cargo area in accordance with the re- quirement of 301. 5 (3). If the equipment is in an enclosed space, the space is to be ventilated according to 1201. and be equipped with a fixed fire-extinguishing system according to 1105. and with a gas detection system according to 1305., as applicable.

2. The compressors should be capable of being remotely stopped from a position which is always and easily accessible, and also from the engine-room. Volumetric compressors should be fitted with pressure relief valves discharging into the suction line of the compressor. The size of the pressure relief valves should be determined in such a way that, with the delivery valve kept closed, the maximum pressure does not exceed by more than 10 % the maximum working pressure, The re- quirements of 506. 1 (2) apply to these compressors.

3. If the heating medium for the gas fuel evaporator or heater is returned to spaces outside the cargo area it is to first go through a degassing tank. The de-gassing tank is to be located in the cargo area. Provisions are to be made to detect and alarm the presence of gas in the tank. The vent out- let is to be in a safe position and fitted with a flame screen.

4. Piping and pressure vessels in the gas fuel conditioning system are to comply with Sec 5.

1505. Special requirements for boilers

Where main boilers or aux. boilers using gas fuel is installed on vessels, their installation is to comply with the requirements in Pt 7, Ch 5, 1605. of the Rules.

1506. Special requirements for gas-fired internal combustion engines and gas-fired tur- bines

Where dual fuel engines or gas-fired turbines are installed on vessels, their installation is to comply with the relevant requirements in Pt 5, Ch 2 of the Rules.