Any required fixed pressure water-spraying fire-extinguishing system in machinery spaces is to be provided with spraying nozzles of an approved type.
The number and arrangement of the nozzles is to be such as to ensure an effective average distribution of water of at least five litres per square metre per minute in the spaces to be protected. Where increased application rates are considered necessary, these will be specially considered. Nozzles are to be fitted above bilges, tank tops and other areas over which oil fuel is liable to spread and also above other specific fire hazards in the machinery spaces.
The system may be divided into sections, the distribution valves of which are to be operated from easily accessible positions outside the spaces to be protected and which are not to be readily cut off by fire in the protected space.
The system is to be kept charged at the necessary pressure, and the pump supplying the water for the system is to be put automatically into action by a pressure drop in the system.
The pump is to be capable of simultaneously supplying, at the necessary pressure, all sections of the system in any one compartment to be protected. The pump and its controls are to be installed outside the space(s) to be protected. It is not to be possible for a fire in the space(s) protected by the water-spraying system to put the system out of action.
The pump may be driven by independent internal combustion type machinery, but if it is dependent upon power being supplied from the emergency generator, that generator is to be arranged to start automatically in case of main power failure so that power for the pump required by 7.4.5 is immediately available. When the pump is driven by independent internal combustion machinery, it is to be so situated that a fire in the protected space will not affect the air supply to the machinery.
Precautions are to be taken to prevent the nozzles from becoming clogged by impurities in the water or corrosion of the piping, nozzles, valves and pump.