AR 15-6 R-1-vt of invest 19ation, Fire Explosit)ij ac

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         h . The source of ignition and sustaining fuel for this fit
    cannot be determined with absol'ute certainty. Technical
    information and testimony provide convincing evidence that the
    cause of the fire was a malfunctioning heater. Very likely, the
    heater had firled with fuel, possibly leaking the excess into. a
    heater duct where fuel accumulated, or left a resirlue, over
    several days. The intermittent operation 'of the heater indicate
    an electrical problem which may have caused the initial spark,
    either because the heater switch was on when the master power
    switch was turned on or because the blower motor activated baie~
    on the ambient temperature in the combustion chamber. The numb-
    of times the heater switch had been kicked or accidentally turne
    on by inexperienced drivers during the recent field problem
    sugge~sts the former was more likely. Another source of ignitior
    coukd have been the heater igniter. The technical advisors for
    thi. . investigation do not have the necessary expertise to make
    any more definitive judgments. The findings in this area were
    givd6 to the Army Safety Investigatio-p Board, conducting a
    parallel inquiry, because they are better equipped to deal with
    this issue.
    
              (1) Two other sources of ignition in the area of'the
    fire are the fuel pumps at the lower left of the heater., Both
    pumps would have been activated when the driver turnpd on the Al
    to open the rear door, providing a spark if either were poorjy
    g~ounded- This is a less likely sclurce of ignition than the
    heater. The driver, upon additional informal questioning, said
    he thinks the fire started when he turned on the master pevwer
    switcg rather than the APU switch because of the amount of
    accumulated smoke.
    
               (2)  Witnesses describe the fire as appearing to be
    between the ammunition racks and, later, as coming out of the
    metal floor duct behind the left ammunitiQn rack. These
    des~:riptions suggest that, regardless of the reason fo ' r the StA.*
    of the fire, it was initially sustained by excess fuel in the
    heater and fuel that had spilled or leaked out and accumulated
    the metal duct. (See Annex U for photographs.)
    
              (3) Even if the crew compartment personnel heater wa:
    not the direct cause of this particular fire, it places crews a
    risk because the fuel can overflow.
    
                     (4)     See Anne- x I for information on previous fires
    associated with the heater.
    
          L.  Surinarv findings regarding th-. fire:
    
             (1) The fire most likely started in the crew
                 -Arsnnno-r] !-ec-trur-
    
                    Tni,it-p:
    
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