Section 4 Gas systems

4.1.1 Means are to be provided to achieve and maintain the required oxygen and/or carbon dioxide levels in the CA zones. This may be accomplished by the use of stored gas, portable or fixed gas generating equipment or other equivalent arrangements. The arrangements are to be such that a single failure will not cause a complete loss of gas supply to the CA zones.

4.1.2 The gas system is to have sufficient capacity to make good any gas loss from the CA zones and to maintain a positive pressure in all CA zones.

4.1.3 The gas system is also to be able to:

1. Deliver gas at 125 per cent of the specified flow rate with two compressors operating.

2. Maintain the specified gas levels in all CA zones when operating 24 hours per day with one unit on stand-by.

4.1.4 Air intakes are to be located to ensure that contaminated air is not drawn into the compressors.

4.1.5 Where it is intended to supply gas by means of stored gas bottles, the arrangements are to be such that depleted bottles may be readily and safely disconnected and charged bottles readily connected.

4.2.1 Fixed gas generating equipment, gas bottles or portable gas generators are to be located in a compartment reserved solely for their use. Such compartments are to be separated by a gastight bulkhead and/or deck from accommodation, service and control station spaces. Access to such compartments is to be only from the open deck.

4.2.2 Gas piping systems are not to be led through accommodation, service and machinery spaces or control stations.

4.3.1 The gas systems are to be designed so that the pressure which they can exert on any CA zone will not exceed the design pressure of the zone.

4.3.2 During initial operation, arrangements are to be made to vent the gas outlets from each generator to the atmosphere. All vents from gas generators are to be led to a safe location on the open deck.

4.3.3 Where gas generators use positive displacement compressors, a pressure relief device is to be provided to prevent excess pressure being developed on the discharge side of the compressor.

4.3.4 Suitable arrangements are to be provided to enable the supply main to be connected to an external supply.

4.3.5 Where it is intended that gas systems are to be operated unattended, the required CA zone environment is to be automatically controlled.

4.3.6 Means of controlling inadvertent release of nitrogen into CA zones, such as locked valves, are to be provided.

4.4.1 The gas supply compartment is to be fitted with a mechanical extraction ventilation system providing a rate of at least 20 air changes per hour based on the total empty volume of the compartment.

4.4.2 Ventilation ducts from the gas generator/supply compartment are not to be led through accommodation, service and machinery spaces or control stations.

4.4.3 The air outlet duct is to be led to a safe place on the open deck.

4.4.4 The gas supply compartment is to be provided with a low oxygen alarm system.