What caused the Armored Personnel Carriers to catch fire?

The M113 APC/ACAV (Armored Personnel Carrier/Armored Cavalry Assault Vehicle) was 100 per cent constructed of aluminum (which has a lower melting point than solid steel), and the M113's were PACKED with ammunition. Primarily with M60 machingun(7.62mm/.308 caliber) and .50 machingun ammo. The total floors were often carpeted with those ammo cans. Sometimes, they were packed with so much ammo that the torsion bars would break after running off road for awhile. During invasions (Cambodia and Laos, etc.) M72 laws and claymores were piled inside to supplement the small arms ammo. Sometimes Bangalore torpedoes were added to the supply. Then add about 100 gallons of diesel fuel. Add all those up; and it's time to "un-a--" the vehicle once it's hit! (Dismount quickly and let it burn).