Module 11.8 Fire protection Flashcards
What is a fire zone?
Area of an aircraft designed to require detectors and/or fire extinguishers and high level of resistance
Fire detection in small turbo prop or piston aircraft tend to use two or more of what detection devices?
- Overheat detectors
- Rate of temp rise detectors
- Flame detectors
- Crew observation
What zones have fixed fire detection?
- APU + engines
- Cargo areas
- Lavs
- Electrical equipment compartments
- Wheel wells
- Bleed air ducts
Fire warning systems are installed to alert the crew of what?
Warn of fire or overheating that could lead to a fire
What detectors may be used on larger aircraft? (Fire related)
- Rate of temp rise
- Radiation sensing
- Carbon monoxide
- Combustible mixture
- Smoke
- Overheat
- Optical
- Observation
What happens when an overheat condition is detected?
Illuminate light and audible alarm
What are the most common fire detection systems?
- Thermal switches
- Thermal couples
- Continuous loop sensing elements
How are the thermal switches connected in a circuit?
Switches in parallel but in series to indicator lights
How are the circuits tested?
Pressing a push-to-test button that operates an auxiliary circuit
The test in a thermoswitch circuit can not check for what?
Serviceability of the individual thermoswitches. Only tests general serviceability of the circuit
Thermocouples do not give warning when what occurs?
Slow increase in temperature or shorting
How does the testing system work in a thermocouple system?
Heating element activated that heats the hot junction
What does a Fenwal continuous loop system consist of?
Inconel tube with a nickel wire inside it. The nickel wire is surrounded by a eutectic salt
How does the Fenwal system work?
Small current passed through the nickel wire, if the housing is heated then the eutectic properties change and resistance drops. This completes a circuit and lights a warning light
What is the additional part in a Kidde system?
An earth wire next to the nickel wire. It is earthed to the inconel tube
Why is a dual loop system used?
Both most be activated to activate alarm, allows for reliability of results. If one is damaged then the remaining one can still give alarm
How are pneumatic sensors made to ensure reliability?
Mechanical damage does not cause false alarm
What are the two types of pneumatic sensing?
- Average
- Discrete
How is the average temp sensing activated?
Expanding of fixed volume of helium
When would hydrogen gas be released into detector cone in discrete sensing?
If a small section of the sensor is heated for 5 seconds in the temp range (1100C)
How is the switch closed in lindberg etc. system?
- Helium pressure increase
- Hydrogen release
What should sensing elements be maintained and inspected for?
- Cracking or damage
- Abrasion
- Things that may cause a short circuit
- Condition of the rubber grommet
- Dents and kinks
What are the two basic types of smoke detection?
- Ionisation
- Photoelectric
How does the photoelectric system work?
Light shone across sample if light is reflected into photodiode then the resistance drops allowing an output to the AFOLTs system
What happens if smoke flows through the chamber in an ionisation system?
Current on reduced due to a reduction in ionisation
Cargo smoke detector systems use what method?
Optical
How do optical detectors work?
Air goes through condensers to remove moisture it is then heated. The amount of light that is reflected onto the scatter detector will raise an alarm
What aircraft require smoke detectors in the toilet?
Over 20 people
What must the lavatory be equipped with?
Smoke detector and extinguishing system
What zones have fire extinguishing system?
- Engines
- APU
- Forward and aft cargo bay
- Lavatories
What do the fire extinguishing bottles hold?
Halon 1301 pressurised with nitrogen gas
What safety mechanism do fixed bottles have?
They have a diaphragm that fractures to stop the bottle exceeding test pressure in the event of excessive temp exposure
What are the two cartridge disk release methods?
- Standard type, slug driven into the diaphragm
- High temp/hermetically sealed, direct explosive impact to rupture prestressed CRES diaphragm
What may some bottles be equipped with?
Basic visual indication pressure gauge
What is the only location where fixed extinguishers are auto discharged?
- Lavatories
- APU
What is a combination gauge?
- Gives bottle pressure
- Electrical signal if the pressure is lost
What is commonly used in fixed fire bottles and the problem with this?
Halon 1301, can not be produced and new aircraft produced after 28/11/24 can not use it
what is a two way check valve?
Used on twin engine aircraft to prevent extinguisher agent from a second bottle backing up into the past emptied main container
What are the two types of commonly used discharge indicators?
- Thermal discharge (Red)
- Discharge indicator (Yellow)
What does the ejection of a red disk mean?
That the contents was ejected due to overheat and the bottle will need replacing
What does the ejection of a yellow disk?
The bottle has been discharged by flight crew input. Replace the bottle pre flight
How are fire bottles operated?
Electrically after flight crew selection
When is a APU extinguishing auto?
During ground servicing/operations
What systems must be followed with regards too regulation of release of extinguisher agent?
Two shot
What must be done prior to discharge of agent?
Isolate from systems and shut down
What fractures the diaphragm in the extinguisher bottles?
Squib
What is the purpose of the guard on the extinguisher button?
To stop accidental operation
What happens when the fire push button is pressed?
- Engine driven generator switched off
- All associated bleed air valves close
- Low pressure fuel shut off valves closed
- Hydraulics closed
- Central warning systems update the Cockpit display
Fire bottles are armed
Abu’s are self monitoring and designed to do what?
Auto shut down
If fire is still present after 30 seconds of bottle 1 discharge, what needs to be done?
Discharge bottle 2
What are the methods of checking the fire bottles are full?
Weight of the bottle and pressure of the nitrogen
How is a bottle pressure check done?
Take readings and check against a pressure-temp graph
Are discharge cartridges (squibs) life limited?
Yes, calculated from the manufacturers stamp typically 5 years with a max of 10
How is it indicated that there is still a fire after bottle discharge?
Red light illuminated
How are the effects of HIRF on squibs minimised?
- Screen RF sensitive cables
- HIRF and RADHAZ filters
- Place sensitive equipment in a faraday cage
- Ensure bonding of components is within parameters
How are the squibs and discharge valves supplied to the maintenance organisation?
Disassembled, usually with a swivel nut aswell
Wha are the twi types of cargo fire extinguisher discharge systems?
- Dump
- Metered (Over 180 mins)
When are master warning lights and aural alarms prevented?
During take off (Not gonna get asked this)
When will Halon 1301 be discharged in the lavatory?
Solder melts when temp gets to 76C
What do the system tests do?
Check the continuity and arming
What affects the number of portable fire extinguishers in the cabin?
Number of passenger seats installed
What are the fires that halon 1301 and halon 1211 can and can’t be used on?
Can: Class A, B, C
Can’t: Class D
Halon is being replaced by what?
HFC
Where are CO2 extinguishers used?
On the ramp to extinguish exterior fires
Dry powder extinguishers are used for what?
Class A, B, C
Water extinguishers are used for what class of fires?
Class A
What extinguishers are unsuitable for cabins and flight deck use?
- CO2
- Dry chemical
- Specialised powder (suitable for ground ops)
What are the 3 things that categories a fire zone? (I.e. class A compartment)
- Inflight access
- Presence of detectors
- Fire extinguishers available
