This article is from the Holocaust FAQ, by Ken McVay firstname.lastname@example.org with numerous contributions by others.
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.