Pyrogen suppression of aircraft electrical fires

Test were conducted at The Memphis Groups facilities in Greenwood Mississippi 29 April-12 May 2000. Under a Improved Airliner Safety Program (IASP), sponsored by the Secretary of the  Navy's Office of Safety and Survivability's,  Aircraft Wiring and Inert Gas Generator Working Group (AWIGG).  Electrical polyimide wire fires were induced in the EE Bay and aircraft galley along with wires suspended over class B fuel pans. Test were supervised and data collected by the NAVAL RESEARCH LABORATORY under the direction of Dr. Frederick W. Williams, NRL Code 6180.

Why is Pyrogen better than an Inert Gas Generator?

Pyrogen chemically extinguishes fires, holds down reignition
"NOT JUST  BLOW THEM OUT MECHANICALLY"


 A 20 ga aircraft wire bundle was removed form the test aircraft interior. 128 each of these were tied into a typical harness and burned in the vertical position to reproduce the worse case electrical fire. These were suspended over a 200 mm cup of Class B fuel to simulate a fuel leak soaking into a wire bundle. Six additional 25 mm class B cups were placed throughout the EE Bay and Radar Bay to insure total flooding of the entire compartment.

Pyrogen Generators were placed throughout the EE bay providing total coverage through the lower lobe forward of the forward cargo bay bulkhead to the nose radome below the cockpit floor (aprox 15 cubic meters). Generators were place so the discharge was pointing away from the fires and only the chemical extinguishment of the aerosol was used to control the fires.


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Pyrogen aerosol in suspension in the ee bay 15 minutes after discharge. Air Stairs cover has just been removed. The aerosol cloud is still in the ee bay providing fire suppression


click photo for larger view

Both EE Bay and Galley fires we tested.
In the Galley Test Series, an aft galley was removed from another aircraft. The wire bundle and 200 mm fuel cup were placed in the bottom floor of the galley, a single Pyrogen generator was placed in the upper portion of the galley test fixture. A viewing window was fabricated in the upper storage door to observe the test. The wire bundle was splashed with Jet A and the class B cups ignited. After a 60 second pre burn to insure total involvement of the wire insulation, the doors were closed and the pyrogen discharged. Type K thermal couples monitored the status of four additional fuel cups placed an different levels in the enclosure. All the fires were extinguished immediately. The internal temperature of the wire bundle remained at 400C at discharge. This is  well above the ignition temp of the fuel, as the aerosol removed the stored heat from the wire bundle. Red embers and charcoal were observed on the wires, but no reignition occurred.   Again the discharge of the generator was directed away from the fuel cups to insure no mechanical interaction with the fires occurred.
 
 


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