It became clear that the Falcon 9/9R first stage has an explosive flight termination system. Consensus is, that it was NOT deliberately fired on landing after/before the stage crashed into the ASDS barge.
However, if you watch the video, it becomes clear that there is an initial fire when the stage hits the deck, likely the LOX tank splitting and hitting basically anything. (LOX burns with almost anything. I am exaggerating, but you know what I mean). Probably mixed with the Kerosene left over, but we know the volume was fairly low, in the 300 lbs of fuel range.
Then there is a secondary explosion, and then a very kinetic tertiary explosion.
Possibly one of those was the residual TEA/TEB ignitors burning after the engines hit.
But can the FTS system be triggered, by the heat of the fire otherwise. It is an explosive. You can have explosives that are very hard to trigger, but a LOX/RP1 fire can burn pretty hot.
Not knowing the nature of the explosive chosen for the FTS, is it possible it ignited on its own due to the heat of the rest of the goings on?
The video coming in has been amazing! From a chase plane, you can see the stage come right into the barge, land, cold gas system valiantly try to hold it upright, till it tips. This video shows the additional explosions.
There is a great video from the barges perspective here.