"the Saudia L-1011 disaster in 1980 has never been given a root cause of the fire that destroyed that aircraft"
AFAIK the fire burnt through from the aft cargo through the aft cabin floor. The controls to the outflow valves were burnt through - they remained closed, keeping the cabin pressurized.
The pax stampeded into the cockpit crushing the crew and preventing the engines from being shutdown - they kept running and pressurizing the cabin.
The cabin crew could not open the doors due high diff.
E&OE