Page 265 - Introduction to Marine Engineering

240 Fire fighting and safety

A system of hydrant outlets, each with an isolating valve, is located
around the ship, and hoses with appropriate snap-in connectors are
strategically located together with nozzles. These nozzles are usually of
the jet/spray type providing either type of discharge as required. AH the
working areas of the ship are thus covered, and a constant supply of sea
water can be brought to bear at any point to fight a fire.
While sea water is best used as a cooling agent in fighting Class A fires
it is possible, if all else fails, to use it to fight Class B fires. The jet/spray
nozzle would be adjusted to provide a fine water spray which could be
played over the fire to cool it without spreading.
An international shore connection is always carried on board ship.
This is a standard size flange which is fitted with a coupling suitable for
the ship's hoses. The flange is slotted in order to fit any shore-side fire
main and enable water to be brought on board a ship lying alongside.

Automatic water spray
The automatic spray or sprinker system provides a network of sprinkler
heads throughout the protected spaces. This system may be used in
accommodation areas, and in machinery spaces with certain variations in
the equipment used and the method of operation.
The accommodation areas are fitted with sprinkler heads which both
detect and extinguish fires. The sprinkler head is closed by a quartzoid
bulb which contains a liquid that expands considerably on heating
(Figure 13.9). When excessively heated the liquid expands, shatters the
bulb and water will issue from the sprinkler head. A deflector plate on
the sprinkler head causes the water to spray out over a large area.
The water is supplied initially from a tank pressurised by compressed
air (Figure 13.10(a)). Once the tank pressure falls, as a sprinkler issues
water, a salt water pump cuts in automatically to maintain the water
supply as long as is necessary. The system is initially charged with fresh
water to reduce corrosion effects.

Valve and
gasket

Spray
deflector
Figure 13.9 Sprinkler head