MODULE 02: FIRE PROTECTION SYSTEMS

• Fire - one of the most dangerous threats to an aircraft, the potential fire zones of modern multiengine aircraft are protected by a fixed fire protection system
• Fire Zone - an area, or region, of an aircraft designed by the manufacturer to require Fire Detection and/or Fire Extinguishing Equipment and a high degree of inherent fire resistance
• Fixed – the term describes a permanently installed system in contrast to any type of portable fire extinguishing equipment, such as a Hand-Held Halon or Water Fire Extinguisher
• A complete fire protection system on modern aircraft, and on man older aircraft, includes a:

  ·       fire detection system

  ·       fire extinguishing system
• Typical zones on aircraft that have a fixed fire detection and/or fire extinguisher system are:

   

  1. Engines and auxiliary power unit (APU)

  2. Cargo and baggage compartments

  3. Lavatories on transport aircraft

  4. Electronic bays

  5. Wheel wells

  6. Bleed air ducts
• Two – no. of operating systems that Fire protection systems on aircraft usually consists
•  

  Two Operating Systems:

  ·       fire or overheat detection

  ·       fire suppression or extinguishing
• In some cases, the systems can be interconnected so extinguishing takes place AUTOMATICALLY when a fire is detected.
• NFPA – National Fire Protection Association
• Methods for detecting fires in reciprocating engine and small turboprop aircraft

  • Overheat detectors
  • Rate-of-temperature-rise detectors
  • Flame detectors
  • Observation by crewmembers
• Aircraft fire protection systems detection methods

  • Rate-of-temperature-rise detectors
  • Radiation sensing detectors
  • Smoke detectors
  • Overheat detectors
  • Carbon monoxide detectors
• Classes of Fires:

  -          Class A - fires involving ordinary combustible materials

  -          Class B - fires involving flammable liquids

  -          Class C - fires involving energized electrical equipment

  -          Class D - fires involving combustible metals
• Three detector system types in common use:

  -          thermal switch

  -          thermocouple

  -          continuous loop
• Thermal Switch System - has one or more lights energized by the aircraft power system and thermal switches that control operation of the light(s)
• Thermocouple System – depends on the rate of temperature rise and does not give a warning when an engine slowly overheats, or a short circuit develops
• Continuous-Loop Systems – it is almost exclusively use by transport aircraft for powerplant and wheel well protection
• Two widely used types of continuous-loop systems:

   

  -          thermistor type detectors

  -          pneumatic pressure detector

   
• Fenwal System - uses a slender Inconel tube packed with thermally sensitive eutectic salt and a nickel wire center conductor
• Kidde System – a system where two wires are imbedded in an iconel tube filled with a thermistor core material
• Classes of Fire Zones:

  • Class A Zone
  • Class B Zone
  • Class C Zone
  • Class D Zone
  • Class X Zone
• Class A Zone - area of heavy airflow past regular arrangements of similarly shaped obstructions
• Class B Zone - area of heavy airflow past aerodynamically clean obstructions
• Class C Zone - area of relatively low airflow
• Class D Zone - area of very little or no airflow
• Class X Zone - area of heavy airflow and of unusual construction
• Smoke detection systems - systems are usually installed to monitor the condition of the air in cargo and baggage compartments
• Two common types used in smoke detection system are:

   

  -          light refraction

  -          ionization
• Light Refraction Type – a type of smoke detector that contains a photoelectric cell that detects light refracted by smoke particles
• Ionization Type – a type of smoke detector that generates an alarm signal (both horn and indicator) by detecting a change in ion density due to smoke in the cabin
• Toxic Gas detectors - usually installed in cockpits and cabins, where the presence of the gas would affect the flight crew and passengers
• Carbon Monoxide - a colorless, odorless gas that is a byproduct of incomplete combustion
• Smoke and flame detectors - operate according to several different principles. Among these are light detection, light refraction, ionization, and the change in resistance of a solid-state semiconductor material
• Optical sensors - often referred to as flame detectors, are designed to alarm when they detect the presence of prominent, specific radiation emissions from hydrocarbon flames
• The two types of optical sensor:

  • infrared (IR)
  • ultraviolet (UV)
• Halogenated Hydrocarbons (Halons) - have been practically the only fire extinguishing agents used in civil transport aircraft
• Halon - an ozone depleting and global warming chemical, and its production has been banned by international agreement
• Two types of Halons are employed in aviation:

  
  

  -          a total flooding agent: Halon 1301

  -          a streaming agent: Halon 1211
• Carbon dioxide (CO2) - an effective extinguishing agent. It is most often used in fire extinguishers that are available on the ramp to fight fires on the exterior of the aircraft, such as engine or APU fires
• Dry powder - chemical extinguishers best control class A, B, and C fire but their use is limited due to residual residue and clean up after deployment.
• Water – best control class A type fires by cooling the material below its ignition temperature and soaking the material to prevent re-ignition.