Page 167 - The Jet Engine

Fire protection

Fig. 14-4 A typical fire extinguishing system.

FIRE EXTINGUISHING extinguishant is discharged from the containers
through a series of perforated spray pipes or nozzles
20. Before a fire extinguishing system is operated, into the fire (fig. 14-4). The discharge must be
the engine must be stopped to reduce the discharge sufficient to give a predetermined concentration of
of flammable fluids and air into the fire area. Any extinguishant for a period that may vary between 0.5
valves, such as the low pressure fuel cock, that seconds and 2 seconds. The system is generally one
control the flow of flammable fluid must be situated that enables two separate discharges to be made.
outside the 'hot' zone to prevent fire damage
rendering them inoperative. ENGINE OVERHEAT DETECTION

21. After a fire has been extinguished, no attempt 23. Turbine overheat does not constitute a serious
must be made to start the engine again as this would fire risk. Detection of an overheat condition, however,
probably re-establish the fluid leak and the ignition is essential to enable the pilot to stop the engine
source that were the original causes of the fire. before mechanical or material damage results.
Furthermore, the extinguishing system may be
exhausted. 24. A warning system of a similar type to the fire
detection system, or thermocouples suitably
22. The extinguishant that is used for engine fires is positioned in the cooling airflow, may be used to
usually one of the Freon compounds. Pressurized detect excessive temperatures. Thermal switches
containers are provided for the extinguishant and positioned in the engine overboard air vents, such as
these are located outside the fire risk zone. When the the cooling air outlets, may also be included to give
relevant electrical circuit is manually operated, the an additional warning.

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