The claim is often heard that it takes 20 hours to air a room which was disinfected with Zyklon-B, and therefore the eyewitness accounts giving a time of 20-30 minutes from when the gassing started to when the bodies where carried out is impossible, because the people carrying out the bodies would perish.

It is true that if one disinfects a building in ordinary commercial use, it should not be reentered within 20 hours. That figure, however, has no meaning relative to the extermination chambers, which were forcibly ventilated. Fifteen minutes was ample time to replace the air after a gassing. When ventilation was not used, the Sonderkommando (prisoners used as forced labor) who removed the bodies wore gas masks. The Germans had plenty of experience with gas, especially HCN, which was widely used for delousing. They knew how to work with it safely. It is absurd to use the 20 hour figure in this context, as it does not assume forced ventilation and takes a huge safety factor into account. The SS didn't care much for the safety of the Sonderkommando who had to enter the gas chambers to take the corpses out in any event. In some cases, these people did suffer from the remaining gas (see, for instance, Pressac, p. 473)

Furthermore, what makes ventilation difficult and lengthy is the presence of rugs, furniture, curtains, etc. Needless to say, these were not present in the gas chambers - there was just bare concrete, making ventilation very fast and efficient.

If the "20 hours ventilation period" above was true, this would mean that the corpses of people executed using cyanide gas in US prisons would remain tied to the chair 20 hours after they were killed...clearly nonsense, as Fred Leuchter, who claims expertise in gas chamber operation, knows full well.

"Cyanide (HCN gas) is notorious as a poison (Gee, 1987) but also is ideal as a chemical weapon. It kills rapidly, dissipates quickly, and leaves no toxic residue."(Somani, Satu M. "Chemical Warfare Agents," Department of Pharmacology, Southern Illinois University, School of Medicine. Academic Press 1992, p. 211)