Fire main: Whilst the various types of portable extinguishers form the front line of attack against a fire detected in its early stages, the fire main or one of the other fixed fire-fighting installations is used if a fire becomes established. The fire main extends to the full length of the ship and from the machinery spaces to the highest levels. Hydrants served by the main, are situated so that with suitable hoses any area on the ship can be reached.
Figure : Cargo ship fire main (R. C. Dean)
Water is the chief fire fighting medium on a ship and the fire main is the basic installation for fighting fires. The system shown for the cargo ship (Figure 14.1) has two independently powered pumps which are also used for general service and ballast. These pumps supply engine room hydrants and the deck main through the screw down isolating valve which must be accessible from outside of the machinery space. The latter is required to prevent loss of water through damaged pipework in the engine room if, to maintain the deck supply, the emergency fire pump has to be used. The emergency fire pump is shown as being situated in a tunnel, with a supply to the deck main through the tunnel escape and also to the twin hydrants in the shaft tunnel by the engine room watertight door.
The deck main has a drain at the lowest position so that the pipe can be emptied (particularly of fresh water) in cold weather. If this is not done, the pipe can be damaged by the water freezing but more importantly, it will be blocked by the ice and not usable.
