Page 258 - Introduction to Marine Engineering

234 Fire fighting and safety

shouting 'Fire', banging on bulkheads or any action necessary to attract
attention. It is necessary to give an alarm in order to concentrate
resources and effort quickly onto the fire, even if the fire must be left to
burn for a short time unchecked.

Control

Two basically different types of equipment are available on board ship
for the control of fires. These are small portable extinguishers and large
fixed installations. The small portable extinguishers are for small fires
which, by prompt on-the-spot action, can be rapidly extinguished. The
fixed installation is used when the fire cannot be fought or restrained by
portable equipment or there is perhaps a greater danger if associated
areas were to be set on fire. The use of fixed installations may require
evacuation of the area containing the fire which, if it is the machinery
space, means the loss of effective control of the ship. Various types of
both portable and fixed fire fighting equipment are available.

Fire fighting equipment
Portable extinguishers
There are four principal types of portable extinguisher usually found on
board ship. These are the soda-acid, foam, dry powder and carbon dioxide
extinguishers.

Soda-acid extinguisher
The container of this extinguisher holds a sodium bicarbonate solution.
The screw-on cap contains a plunger mechanism covered by a safety
guard. Below the plunger is a glass phial containing sulphuric acid
(Figure 13.4). When the plunger is struck the glass phial is broken and
the acid and sodium bicarbonate mix. The resulting chemical reaction
produces carbon dioxide gas which pressurises the space above the
liquid forcing it out through the internal pipe to the nozzle. This
extinguisher is used for Class A fires and will be found in
accommodation areas.

Foam extinguisher—chemical
The main container is filled with sodium bicarbonate solution and a long
inner polythene container is filled with aluminium sulphate (Figure
13.5(a)). The inner container is sealed by a cap held in place by a
plunger. When the plunger is unlocked by turning it, the cap is released.