Leaving aside the issue of Zyklon B not working that way (it requires a machine to heat it to a high heat, with a blower), the way that "gas chamber" is constructed would result in the Germans being regularly wiped out by the poison gas. Just one example is that there are drains on the floor inside that lead to drainage pipes, which connect up to the drains in all the other buildings. The gas would have killed everyone in all those other buildings each time people were gassed in the "chamber."
Quick question: do you know the difference between Zyclon A and Zyclon B?
If I were you, I'd look into it. Perhaps ask a friend who is good at chemistry.
Ymmv
Also, how does a lighter than air gas do "down" piping?
