An airplane just like any other man made object can be prone to fire. It is therefore deemed necessary to fire proof or eliminate causes of fire in the airplane.
Designated fire zones – engines, auxiliary power unit, wheel wells, cargo compartments, lavatories, bleed air ducts & electronic bays.
N.B – in this case the engine and the auxiliary power unit are isolated by fireproof bulkheads.
THE FIRE DETECTION SYSTEM
- Differential expansion detector – this use the principle that when heat is applied to different materials they would expand at different rates and is used for engine cooling air units
- Thermocouple detector – this depends on rate of temperature rise and only gives alarm when engine overheats.
- Thermal switch system detector – consists of lights operated by switches which complete electrical circuit at certain temperature.
- fenwal spot detector – works without a control unit and on occurrence of an overheat or a fire occurs it causes the switch in a detector to close an alarm bell sounds and it lights a warning light.
- kidde sensing element detector -In the Kidde two wires are pushed in a cone tube filled with a thermistor core
material and 2 electrical conductors going through the length of the core with a ground connection at the tube with the other conductor connecting to the fire detector. therefore as electrical resistance to the ground decreases, the temperature of the core increases.
- continuous element system – is a continuous element type detector consisting of a stainless steel tube. This element absorbs gas in proportion to the temperature value selected.
- overheat warning systems – are placed on an aircraft to indicate high temperature areas that would cause a fire.
There are also smoke, carbon monoxide and flame detectors in a plane that work closely with the fire detection system. They include sensors that are either optical, using light sensors or ionizing, utilizing small amount of radio active material.
CLASSES OF FIRE
The following are the classes of fire as pertaining aircraft : –
- CLASS A – these are fires involving ordinary combustible materials such as plastic, wood, paper ,cloth, rubber e.t.c
- CLASS B – these are fires involving flammable liquids such as petroleum, oils, tar alcohol e.t.c
- CLASS C – these are fires involving electricity or electrical equipment e.t.c
- CLASS D – these are fires involving combustible metals such as magnesium, titanium, lithium, potassium, sodium e.t.c
- BCF – bromochrolodifloromethane is a commonly used agent, also known as halon 1211. It is stored in signal red, purple, brown or green containers. it is used in electrical and flamable liquid fires i.e class C & B.
- BTM – bromotrifloromethane – also known as halon 1301. it is stored in grey containers. it is used for protection of auxillary power units, power plants and cargo compartments.
- Water or water glyco – stored in red or grey containers and is used in hand held portable devices.. used in fires involving domestic materials
- chemical/dry powder – entinguishant is stored in blue or red container with a blue label. it is quite effective in fires involving flammable liquids,wood,fabric, paper i.e class A & B. it is used mostly in wheel and brake fires.
- carbon dioxide – stored in black or red container with black label. used as hand held extinguishers. is capable of extinguishing fires of many classes.
- foam & sand – used on flammable liquid fires . Sand is is used in containing metal fires such as magnesium and titanium. i.e class B & D.