How about using some common sense and despatch a couple of units to fight the fire leaving a complement that is sufficient for normal operation then IF the fire gets out of control summon the rest for assistance.
I have often wondered about how many airport firecrew members get to go through an entire career without every being called out to a live incident. I hope there are loads of them. However, wondering is all I do, because I understand why they are there, and they are part of the reason why the airline industry is so safe.
So to hear repeatedly on this thread that this is just a "minor" problem, or that they should use "common sense" is frankly getting rather tedious.
By the same logic, let's have an option button on 999 so that in addition to police / fire / ambulance, you also get to pre-determine whether it is trivial, serious or life threatening. Daft? Of course it is, so why do you expect any different at Heathrow? Is there not also the small question of smoke from a fire meaning loss of visibility?
The whole point of contacting the emergency services is that you let the experts make any decisions about when it is safe to return to normal. One report said LHR's runways were operational again after about an hour. That sounds pretty good to me, well done to all concerned - and time for the ill-informed to show some appreciation of that.