If a battery fire can destroy 1500 vehicles in an airport car park, think what it could do in the lower floors of a tall office building. One of the 9-11 aircraft was said to carry 20,000 gallons of jet fuel, which was the actual weapon used by the terrorists to bring those building down. With 90% of 1500 autos, each having a partial tank of gasoline you could easily have that same 20,000 gallons of fuel. And access to such an office building's parking area would be far, far more difficult for the fire department. I don't think you can glibly say that when all the fire departments get the correct tool, the problem is solved. They must get to that FIRST EV in time to actually use that device before the fire spreads out of control.
Building designers aren't idiots. They know car park fires happen. They know that putting an office block on top of a car park that can burn presents additional risk. Depending on the use, the buildings are designed to withstand different fire durations.
In the UK, a regular car park only needs to withstand fire for 15 minutes. That is, the fire can have spread to the next floor within 15 minutes. That sounds crazy at first, but think about it: car parks are wide, open spaces. Evacuation is easy. We care about humans. Cars can be replaced, people can't be. The fire doors and evacuation stairs have to withstand the fire for far longer, usually 60-90 minutes, giving sufficient time for fire fighters to stage an attack and search for anyone who could be trapped. It's notable in the car park fire in Liverpool, UK, in 2018, the car park was totally gutted, but the fire escapes were relatively untouched. There was only a bit of smoke damage, the fire doors had otherwise completely withstood the entire car park going up [1].
For something like a shopping mall, where there might be a populous retail area attached to a multistorey car park, the car park area is designed to contain the fire for as long as possible, with double fire-door systems linking the two (when you next visit one, see how they design this). The populated areas of the shopping mall can be evacuated quickly; the plans are well established. Units that have a large number of people, like a cinema, are placed away from the car park area (and will have their own fire escapes), as these will naturally take longer to evacuate. Fire alarm systems will be linked. The fire won't spread to the retail units for some time, but again, economic cost if it does, no lives lost, no big deal.
Office blocks are more challenging, but usually a substantial concrete foundation barrier will exist between any underground car park and the busy office block. The office block itself will have normal evacuation procedures. If it's big enough it'll have things like backup generators to keep lifts going for evacuation.
I'm sure some fire chiefs fret about fighting these fires, and sure, they're going to be a challenge, but battery-EVs don't make huge car park fires much worse. The majority of energy comes from the burning of the flammable interior and plastics, the battery might add fuel to the, er, fire, but it's really not that much energy compared to the rest of the car. Just on a fundamental physics level, a lithium-ion battery is nearly inert when fully discharged (this is why when transported, EVs are only charged to 10% or so). They can still burn, but much less ferociously. This tells us the energy released from a battery can't be much more than what it is charged up with. Maybe 0.5GJ worst case for some of the biggest SUV EVs.
[1]
https://www.bafsa.org.uk/wp-content/uploads/bsk-pdf-manager/2018/12/Merseyside-FRS-Car-Park-Report.pdf (page 41, 42, showing how good fire door design works)
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