"That's a pretty big assumption"
Fair comment. But looking at the various films and photos its clear something more than just an HV line is on fire. Those flames coming out of the ducts are are gas flames, presumably from a fractured gas main. And how do you account for the loss of telephones and the wider-scale internet outage? And the official statements this morning that it may take "several days" to resolve the fire? It may well be the citadel wasn't the seat of origin - but my guess is that the fire has spread to it. However, I hope I'm wrong.