I'm no firefighting expert, but I'd be in two minds about water sprinklers in that situation - they should certainly help cool things down and so keep more surfaces below ignition temperature, but on the other hand if the problem is fuel flowing over floors, being that most fuels float on water and will often quite happily keep burning in that situation, I'd be worried about the water carrying the burning fuel further and faster than would otherwise have been the case. If the sprinklers were of the traditional glass bulb type that only opened an individual sprinkler head once the fire was reasonably close, I could almost imagine a worst case situations where the sprinklers above the burning fuel had triggered, but the ones above and somewhat ahead of the fire front (where wet cooling would be most effective in preventing subsequent vehicles catching fire) would still be closed, then opening as the fire arrives, just in time to help spread the fuel from the newly ignited cars. Maybe I'm over-thinking this - just put it down to being of the generation that had it drummed into us never ever to put water on chip-pan fires.

Thermal run-away from batteries I'm sure must be a different kettle of fish. It's not a "traditional" fire to my mind - the heating effect isn't at all dependent on a chain reaction involving fuel, heat and oxygen. Do almost what you like you're not going to make much difference to the amount of (heat) energy being produced by current and resistive heating. I guess water would be helpful in cooling neighbouring vehicles, so slowing the spread of fire. I'd almost be less worried about pouring water on an EV than on an ICE vehicle. There may be some nasty voltages in the battery, but (if the vehicle isn't on charge) they're not particularly earth referenced, and if the thing is on fire anyway no-one is likely to get close enough for any risk of a direct shock. I don't know if lithium (in whatever form it is in batteries) reacts with water (like some other metals do).

  - Andy.

'Lithium' batteries are mostly something else, only a few % lithium, and that is bound up in the plates. 

Yes lithium element generates hydrogenand heat on contact with water, as the litium runs off with the oxygen,

The hydrogen takes a  lot of volume or tries to, and is explosive mixed with air in the right concentration.

However, on balance, cooling a lithium battery with water is probably correct - if it is already burst and on fire any elemental lithium has probably gone, and cooling it will save adjacent cells, and an un-burst cell that is cooled is less likely to explode - gas  pressure rising with temp and all that.

The problem can be that there is a lot of electric energy in a charged cell, and once shorted that comes out as heat, and in effect burning continues without air, unlike a  normal fire.

The water may end up being quite unpleasant and needs to be very dilute or deliberately neutralised  before it goes down the drain - some of the metal hydroxides are very caustic.

Mike.

'Lithium' batteries are mostly something else, only a few % lithium, and that is bound up in the plates. 

Yes lithium element generates hydrogenand heat on contact with water, as the litium runs off with the oxygen,

The hydrogen takes a  lot of volume or tries to, and is explosive mixed with air in the right concentration.

However, on balance, cooling a lithium battery with water is probably correct - if it is already burst and on fire any elemental lithium has probably gone, and cooling it will save adjacent cells, and an un-burst cell that is cooled is less likely to explode - gas  pressure rising with temp and all that.

The problem can be that there is a lot of electric energy in a charged cell, and once shorted that comes out as heat, and in effect burning continues without air, unlike a  normal fire.

The water may end up being quite unpleasant and needs to be very dilute or deliberately neutralised  before it goes down the drain - some of the metal hydroxides are very caustic.

Mike.