13.12 Fire Protection Flashcards
Fire classes
Class A - fuelled by solid combustibles
Class B - fuelled by combustible liquids
Class C - fuelled by gasses
Class D - fuelled by metals that burn
Class E - fuelled by electrical equipment
Fire and explosion protection
Total flood extinguishment
Total flood fire suppression
Streaming fire extinguishment
Explosion suppression
Interior against explosion and fires
Streaming
Is directly applied to the area
Total flood
Is an entries compartment flooded to suppress fire
Overheat detection
Detects high temp
Aircraft fire zones
Class A - visual detection of smoke and accessible to a fire extinguisher
Class B - approved smoke detectors or fire detector that issues fire warning in flight deck - crew operated extinguisher
Class C - approved smoke detector or fire detector with flight deck warning and a fire suppression system
Class D - removed in 1998
Class E - cargo aircraft only smoke or fire detector system alerts flight deck allows air flow shut off to suppress the deck
Fire detector types
•Melting link switches
•Thermocouple detectors
•Differential expansion switch
•Continuous wire type detectors
- resistance type (resistance decreases with increase in temp)
- capacitance type (capacitance increases with an increase in temp)
• thermal switches - bimetallic switch that if heated makes contacts and activates a warning.
• thermocouple - 2 wires joined at a junction with a insulated reference thermocouple. A sharp rise in temp on the thermocouple but not the reference thermo couple will cause a current flow
Fenwall system
Single wire surrounded by continuous string of ceramic beads in an Inconel tube. Beads wetted by eutectic salt.
Normal temps salt prevents current from flowing.
In a overheat fire condition core resistance drops & current flow between the signal wire & ground energising the fire alert/alarm system
Kidde system
Two wires are embedded in a special ceramic core within a Inconel tube. One of the wires is welded to the case at each end & acts as an internal ground. The second wire is a hot lead (above ground potential) that provides an electrical current signal when the ceramic core material changes its resistance with a change in temp
Kidde sensing elements
Are connected to a relay control unit, constantly measures the total resistance of the full sensing loop.
The system senses the average temp and any hot spots
Fenwall and kidde
Both continually monitor temp in a compartment and will automatically reset following an alarm or overheat condition
Pneumatic type fire/ overheat detectors
Two functions average temp threshold or localised discrete temp caused by fire or localised heat spots
Lindberg system
Continuous element type detector a stainless steel tube containing a discrete element. The element has been processed to absorb gas in proportion to the operating temp set point.
When temp rises to the operating set point the heat generated causes the gas to be released from the element.
The gas causes the pressure in the stainless tube to increase, this actuates the diaphragm switch in the responder unit and activates the warning system
Lindberg System test
Low voltage AC is sent through the outer sheath of the element, when these current heats the sheath to the required temp, the element will release gas and activate the system. Release the test switch and the detector will cool off and contacts open ending the warning.
Systron donner system
Titanium centre wire, centre wire contains hydrogen, contained within a stainless steel tube that is surrounded with helium.
Systron Donner
As the system is heated, it will release hydrogen into the helium filled tube this will cause the pressure to increase with temp increasing cause the pressure switch to trip at the determined pressure causing the fire/overheat warnings
False alarms
Mechanical damage to a pneumatic sensor tube will not cause a false alarm
Severe damage such as a sensor wear through will cause a loop fault message
Fire warning generation
Fire on loop A & loop B
Fire on loop A & fault on loop B
Fault on loop A & fire on loop B
Fault on both loops within 5 secs of each other - Fire burn through
Loop fault warning
Electrical failure
Failure in a detector
Failure in a detection circuit
Detection of a single loop fire for 20s or more while the other loop is normal
Detector installation
Continuity + insulation checks
Clipped 4” from end fittings
Clipped every 6”
Clip bushes fitted
Adhere to bend radius limits
Maintain clearances from structure to avoid fretting
Unit detector systems
Usually simple DC circuits
Usually several detectors connected in parallel so if one detector closes the switch it will cause an alarm
False fire warning possible causes
Ingress of moisture
Faulting installation
Lack of cleanliness
Well rounded inspections can help reduce faults and improve reliability
Acceptance checks
Function tests
Periodic tests
Cleaning
Smoke and flame detectors (most common)
CO - measures carbon monoxide in the air
Photo electric - measures the amount of smoke in a sample piece of air
Ionisation detectors
Measures current flow through ionised air
Visual detectors
Sample air drawn through a chamber
Exstinguishment types
Water - class A fires only
Carbon dioxide - class D and tyre fires
Halon 1301/1211 (most common) - non corrosive, evaporates & leaves no residue. (Halon 1001 discontinued)
Flame detectors - are usually light detectors that are sensitive to infrared light
High rate discharge systems
Nitrogen pressurised bottles holding halon 1211 or 1301. Squibs are used to hold the bottle pressure until the frangible disc is fractured allowing discharge
Periodic checks
Used to check pressures and weights at specific intervals
Discharge cartridges (squibs)
Are a explosive cartridge used to discharge the bottle when selected. Life limited component discharged by electrical current usually 5A 28VDC
Follow amm for installation and testing
APU fire protection
Dual pneumatic loop type system
Protected by a air/ground logic system normally
Ground mode (unattended) the ECU will monitor and shut down and discharge the bottle should it see a fire.
Air mode - allows the crews to monitor and action a fire warning
Cargo compartment fire protection
Class B, C & E have smoke detection crew alerting
Single loop or dual loop detectors
Fire suppression dump bottled then metered discharge bottles
Auto alert then manual extinguishing
Class E compartments allow airflow to be shut off to the compartment then depressurise it.
Lav fire protection
Smoke detection alerts flight deck and cabin
Each receptacle enclosed and constructed of fire resistant materials
Capable of withstanding a fire for 30 mins
Built in fire extinguishers for each bin with a seal on access doors
Extinguishers
Mustn’t cause any damage to the structure when discharging
Must be if capacity to suppress a fire in its designed compartment area and mustn’t be able to enter the cabin space
Waste bin extinguisher
Waste bin extinguisher has a low melting point to discharge temp rise around 71 degrees c and has a temp indicator strip located nearby for indication of fire.
Lav regs
No smoking placards must be fitted
Ashtrays must be fitted
Lavs must be Inspected at a max Interval of 72 hours to confirm all doors seals and latches are serviceable
Avionics smoke detection
Used smoke detectors placed in the cooling system which then alerts and indicates in the flight deck
Portable fire extinguisher
Must be at least 1 in the flight deck
At least 1 in class A, B or E compartment that is accessible to the crew
At least 1 near or in each galley
Halon or pressurised water types
Pax capacity to fire extinguisher
7-30 X1
31-60 x2
61-200 x3
201-300 x4
301-400 x5
401-500 x6
501-600 x7
601-700 x8
