FIRE PROTECTION Flashcards
What do fire systems consist of?
- sensors
- control unit
- warning panels
What is a spot sensor?
Bi-metallic sensor, triggers alarm when closes.
Used for pneumatic duct leak detection
What are fire and overheat sensors?
Continuous loops
Monitor large areas
What is a pneumatic pressure loop? (Systron or donner loop)
A sealed tube which contains gas. When gas expands at higher temp, operates pressure switch (responder)
Each loop contains a semiconductor material. What is the purpose of this?
Decreases electrical resistance with increasing temp. Alarm sounds if resistance between central wire and tube decreases below value
What does a control unit identify?
Identifies the normal and alarm conditions of a sensor with a measurement of resistance.
If a fire is detected, what will the central warning system activate?
Red fire master warning lights, aural warning and a message on the ECAM/EICAS display.
How do you cancel a warning in the cockpit?
Pressing the master warning light
Failure with a bi-metallic switch in the open and closed position causes what?
Open - prevents overheat and fire detection
Closed - false alarm
What advantage do other sensors have over bi-metallic sensors?
Prevention of false fire warning and triggers fault message
What are all essential fire warning systems?
Dual loop systems
2 sensors and detection circuits in the control unit
On a dual loop system, when will the alarm be triggered?
When both sensors detect fire at the same time
Prevents false indication
If the control unit detects a faulty sensor, how do dual loop systems detect fire?
Automatic switching allows the sensor to trigger the warning off just one sensor.
(Message about faulty one on the central warning display)
When should operational checks of the fire system be carried out?
Before engine and APU starts.
How can you find out which sensor is faulty in a system?
Via the central maintenance computer.
What is a semi conductor loop?
Stainless steel tube with semiconductor ceramic material with a wire in the centre
What is the function of the ceramic material in a semiconductor loop?
Acts like endless resistors which have NTC characteristics
On the semiconductor loop which contains 2 internal wires, what is each wire for?
Upper - connected to control unit
Lower - connected internally to ground
(Kiddle loop)
If more than one loop is required and loops are connected, what does this mean?
Resistors are connected In parallel
What is the resistance between for longer and shorter loops?
1 mega ohm for long loops and 10 mega ohm for shorter.
How is dual loop failure made almost impossible?
The closed loop condition is tested during operational tests.
How is a short circuit created?
Rubbing between the structure and loop, causing contact with the internal wire.
What resistance will fire/overheat warnings occur?
500 ohms
In an essential system, how is false alarming from short circuiting protected?
Prevention via the dual loop system.
What are the number of discharge heads on a fire extinguisher equal to?
Number of compartments a bottle must supply.
How much explosive does the discharge cartridge in the centre of the discharge head contain?
Around 400 milligrams.
Class C explosives.
When does the power explode in a discharge cartridge?
When an electric current heats up a wire (the squib) inside the cartridge.
(Sparks can accidentally explode the device)
What is the maximum service life of the discharge cartridge?
6 years.
What is the date on the cartridge bottle?
Date of manufacture.
10 years maximum storage and service life.
What does a pressure switch do on a bottle?
Sends indications to cockpit if level falls between 50%.
Why would the temp in the bottle area increase?
Broken pneumatic duct near bottle or a fire.
Overpressure used as pressure will increase with temp
When does the frangible disc break in the bottle?
When pressure increases to 1700 psi.
3 times normal pressure
What has happened if a red disc is missing from the fuselage?
Fire bottles have over pressured and halon has been released overboard.
(Missing yellow disc near red disc of bottle discharges via spray nozzles)
Is the APU fire system automatic or manual?
Automatic.
What pushes the halon out of the bottle?
Pressure nitrogen.
How is the hot battery bus always powered?
Batteries. (Power source always available)
Why is a broken squib extremely bad?
The extinguishing bottle can no longer be used.
What happens when you test the squib?
Very small current sent through, small enough to not fire off the bottle.
What is a “2 shot system”?
2 fire bottles can be discharged into one engine.
When would a second bottle be discharged?
If the fire has not gone out after 30 seconds.
Where is only a “one shot” system used?
APU.
When does the APU fire bottle release when the APU fire warning is activated?
3 seconds after automatically.
What are the installation limits for loops?
Max bending of no more than 3.2mm
Min radius of 25.4 mm
Gas pressure inside a gas loop is what in comparison to the ambient pressure at sea level?
2 times Higher
How do you know if the pressure switch is open or closed on a gas loop?
With the resistor inside the responder
In a gas loop, when pressure will shut the pressure switch?
High pressure
What does an extinguisher bottle consist of?
Halon 1301 in liquid format pressurised with nitrogen at 600psi
Where are 20kg extinguisher bottles used?
Cargo compartment, largest bottle
Where are 10kg extinguisher bottles used?
Engines
Where are 5kg extinguisher bottles used?
APU
