Do you have a source for the US Army physicians work?       Ok, when you mentioned big iron doors it made me think of that because they used a film clip of the actual iron door of the delousing gas chamber at Dachau while falsely claiming it was the door to the homicidal gas chamber.   I agree, it can be frustrating because there is a lot to study on this subject. I take a camp at a time and just learn all I can on it. What's been said about it and what's been revised.   There was also a U.S. Army physician who preformed nearly 1000 autopsies on dead inmates at Dachau during liberation and found not a single one that died from cyanide or carbon monoxide poisoning. 