Fire Detection and Warnings

Question 1

Overheat Warning Systems

Answer 1

Triggered by hot gases

Risk of damage other than by fire

Question 2

Designated Fire Zones

Answer 2

Area where failure or leakage may pose a fire risk requiring protection
Engines and auxiliary power units protected by a firewall which will prevent further spreading

Question 3

Location of Fire Detectors

Answer 3

Rapid warning of a localised fire or overheat condition
Rear of engine
Wheel wells
Auxiliary power unit
Cargo compartments

Question 4

Fire Warnings in the Cockpit

Answer 4

Red lights

Audible warnings

Question 5

Unit Type Detectors

Answer 5

At points most likely to be affected by fire
Thermocouple detectors
- In engine bays
Bimetallic switch
- When heated two different metals expand at different rates

Question 6

Continuous Type Detectors

Answer 6

Continuous loop (continuous wire loop)
Resistance type
Capacitance type

Question 7

Fire Detection Systems

Answer 7

Fenwall: tube with a single wire
Kidde: tube containing 2 wires embedded in a thermistor core (will sense average and hot spots)

Question 8

Smoke Detectors

Answer 8

Cargo holds, equipment bays
Air from compartment is routed through smoke detectors
Show which compartment is affected
Photo-electric cell
Visual smoke indicators

Question 9

Fire Extinguishing Equipment

Answer 9

Fixed (permanently installed)
Mixed
Portable

Question 10

Extinguishants

Answer 10

Methyl bromide (MB)
Bromochlorodifluoromethane (BCF)
Carbon dioxide (CO2)
Water
Dry chemical

Question 11

Methyl Bromide (MB)

Answer 11

Low boiling point (approx 5 degrees celcius)
Protection of engines
Toxic (not used in cabins)

Question 12

Bromochlorodifluoromethane (BCF)

Answer 12

Electrical and flammable liquid fires

Semi-toxic: vent cabin

Question 13

Carbon Dioxide (CO2)

Answer 13

Electrical and flammable liquid fires

Takes away heat and oxygen

Question 14

Water

Answer 14

Combustible materials only

Not suitable against electrical of flammable liquid fires

Question 15

Typical Fixed Systems

Answer 15

Circuits controlled by switches or handles

Question 16

Triangle of Fire

Answer 16

1. Heat or source of ignition
2. Fuel (material that will burn)
3. Oxygen
   Without one of these components fire will go out

Question 17

Differential Expansion Detectors

Answer 17

Consists of a pair of contacts mounted on a spring bow assembly fitted within an expansion tube
When heat is applied, the tube expands at a greater rate than the bow drawing the contacts together, providing power to the warning circuit
Short time delay before the warning is activated to prevent false warnings

Question 18

Fire Wire Systems

Answer 18

Continuous Loop Fire Detectors
Consists of a tube, with a central electrode insulated by a core of temperature sensitive material
Core has either a negative coefficient of resistance or a positive coefficient of capacitance
Will continue to work with a single break as the loop is connected at both ends
React to isolated temperature increases or if the temperature of the whole detector increases
Positioned around the engine fire zones as a continuous double loop and both must detect a fire to initiate the warning

Question 19

Resistance Continuous Type Detector

Answer 19

As the temp increases, the resistance of the insulating material decreases causing the current to flow between the electrode and the outer tube to increase, until the warning system operates
A short circuit could give a false warning

Question 20

Capacitance Continuous Type Detector

Answer 20

Core material is dielectric
The case and inner electrode are poles connected across an AC supply
Will not give false warnings
As temp increases, the properties of the inner core material change, increasing the capacitance of the detector and the feedback current will reach a level and activate the fire warning

Question 21

Gas Filled Detection System

Answer 21

Consists of a number os sensing elements
Tube has a central core giving off hydrogen gas when heated
Helium gas is forced into the tube under pressure and sealed
Pressure monitored by two switches
Uses the double loop system

Question 22

The Integrity Switch

Answer 22

Closed at the tubes under normal pressure

If damage occurs and helium gas is released the pressure decreases and the switch will open indicating a fault

Question 23

The Alarm Switch

Answer 23

Open under normal pressure
If heated locally, hydrogen gas will be released, pressure will increase and the switch closes initiating the fire warning
If exposed to a hot gas leak, helium pressure will increase and close the switch