Ummm this is a 'unhappy' post! but i sure found it interesting.
Probably should have a warning, dunno.
Anyway Fred Leuchter is the only living designer of Gas Chambers, basically he says that the holocaust couldn't have happened because of a number of reasons, one being there simply wouldn't be enough gas to do the job, it's also a very expensive and impractical method, another the gas is cyanide and would need to be released in a totally sealed chamber, not an old building with wooden doors, also after gassing it takes some 3 days for the place to be clear to be able to enter it. and having more that 2 people would take weeks.
Other reasons in the podcast.
Distressing stuff i know, but worth sharing i thought, as one of the more convincing arguments about this matter.