Page 267 - Introduction to Marine Engineering

242 Fire fighting and safety

systems and the mist has proved effective against liquid fuel fires, making
it suitable for use in machinery spaces.
Research is continuing, in particular as to the effectiveness of mist in
a large machinery space. Water mist is accepted as a fire extinguishing
agent, with respect to SOLAS fire protection requirements.

Foam systems
Foam spreading systems are designed to suit the particular ship's
requirements with regard to quantity of foam, areas to be protected, etc.
Mechanical foam is the usual substance used, being produced by mixing
foam making liquid with large quantities of water. Violent agitation of
the mixture in air creates air bubbles in the foam.
An automatic foam induction system is shown in Figure 13.11. The
automatic inductor unit ensures the correct mixing of water and foam
compound which is then pumped as the foam making solution to the
hydrants for use. The foam compound tank is sealed to protect the
contents from deterioration and has linked compound supply and air
vent valves. To operate the system these two linked valves are opened
and the fire pump started. Foam mixing is carefully rnetered by the
automatic inductor unit. The fire pump and compound tank must be
located outside the protected space.
High-expansion foam systems are also available where a foam
generator produces, from foam concentrate and sea water, a thousand

Deck main
Linked air stop valve
and foam
valves Machinery space
main stop valve
Flushing vatve
(normally shut)

Foam
hydrants
Drain v
valve T Flushing
1 valve

Non return
valve

Foam
Strainer Sea Automatic making
f water inductor Fire solution
unit
Figure IS. 11 Foam induction system