Page 257 - Introduction to Marine Engineering

Fire fighting and safety 233

Figure 13.2 infra-red flame detector

Heat detectors can use any of a number of principles of operation,
such as liquid expansion, low melting point material or bimetallic strips.
The most usual detector nowadays operates on either a set temperature
rise or a rate of temperature rise being exceeded. Thus an increase in
temperature occurring quickly could set off the alarm before the set
temperature was reached. The relative movement of two coiled
bimetallic thermostats, one exposed and one shielded, acts as the
detecting element (Figure 13.3). Heat detectors are used in places such
as the galley and laundry where other types of detector would give off
false alarms.

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Figure 13.3 Heat detector

Alarm
Associated with fire detectors is the electric circuit to ring an alarm bell.
This bell will usually sound in the machinery space, if the fire occurs
there, and also on the bridge. Fires in other spaces will result in alarm
bells sounding on the bridge. Any fire discovered in its early stages will
require the finder to give the alarm and or make the decision to deal
with it himself if he can. Giving the alarm can take many forms such as