The Batteries in question are serious trouble, I would think the Fire Fighters were aware of the risk and stayed clear. They tend to spit and fizz a bit as each cell reaches ignition temperature. These little batteries are multi cell and, if damaged or defective, can go into "thermal runaway". All it takes is one cell ( batteries can have 36 or probably more these days) to overheat and a chain reaction starts. Testing has shown temperatures over 1000 degrees celsius to occur in only a couple of minutes. Remember the pictures of the melting superstructure of Frigates in the Falklands? Apply that to an aircraft in flight and you get the picture.