....Some speculation that oxygen on the bus was the culprit....
or some one smoking near the oxygen. There also needed to be something to explode. Oxygen needs some fuel to actually combust.
Any thing that can burn will burn much faster in a enriched Oxygen environment.
During gas shortages there are a lot of people carrying around those red plastic tanks...
Oxygen enriched enviroment with lots of old folks on O2 all it would take is a electric spark or some fool with a lit cigarette dropping a cherry on a seat cushion & you got a serious bonfire literally in nothing flat.