When these batteries burn, they can’t be put out except by cooling them down somehow because they contain their own oxidizer. So fire departments tend to just let them burn and send whatever metals and other chemicals into the atmosphere. A gasoline fire can be put out with fire suppressants that deprive it of air. Apart from that, the batteries are also hazardous in terms of their manufacturing and disposal lifecycle and also just by making vehicles heavier. Heavier vehicles mean more energetic collisions and they also require bigger brakes, which means more brake dust pollution.