Toyota Rav4 flaming out, is it the petrol tank or the bat electrolyte or both or neither?!
Battery electrolyte isn't flamable (at least if we are talking normal lead acid car battery) - that's sulfuric acid + water.
The video shows a bleve of a petrol tank. I had the "pleasure" to witness this first hand few times. Yobs love to set cars on fire for fun here (yay France) and when the car burns for a while, the tank will heat up and pressurize until it (or the fuel pipe) bursts - that's what you see. It is not really an explosion in true sense (detonation) but the pressurized fuel vapors escaping the ruptured tank and igniting with a large WHOOSH (and sometimes a bang of the tank bursting).
An even worse event that will eventually happen if the fire isn't extinguished rapidly is the tires bursting in the heat - that's an enormous BANG and it sends shrapnel all over the place.
These firemen have only themselves to blame there, IMO.
Here when the fire crew arrives on the scene and it is obvious that the car is burning for a while already, they will
never approach the vehicle on foot. They can't know when will the tank or tires blow. That could cause a serious injury or even kill a man, despite full protective gear. They will always use the water cannon from the truck first to reduce the fire and to cool the vehicle down from distance. Only then they approach on foot with the hoses to finish the job.