The man who built most of the American gas chambers was actually commissioned to do a report on some of the chambers at Birkenau and other camps. He determined that they weren't gas chambers, and had they been used as such it'd have poisoned the whole camp, as the vents into and out of the chamber were connected to the rest of the building's ventilation.
https://odysee.com/@Blackpilled:b/leuchterc:1