This is just speculation, but I base it on my actual experience in commercial nuclear power at Browns Ferry Nuclear Plant, where one of the worst 'almost' accidents occurred in 1975. This was the infamous instrumentation cable fire started by a candle. Not to get into the detail (you can easily google it) but the bottom line is the fire seals on the cable trays and the wall penetrations where the cables ran from the control room to the reactor building failed. The seals themselves caught fire and destroyed the cables. Poor design and material selection.
So, based on initial assessment reports this morning - that the actual diesel engines appear fine and would otherwise function - I'd be looking at the fireproofing on the cross-connect cables between the split (forward and aft) electrical distribution systems. As noted in this article
Paul and I put together last evening with the great help of Triumph guest Jim, the smells were definitely of an electrical fire.