[Off topic comments deleted by Moderator]
BUT, I do feel it necessary to point out something else about humidity and HCN. Mathis does have the humidity/temperature relationship backwards, there's a reason why Leuchter emphasizes that gas chambers must be kept DRY.
HCN is extremely soluable in water. In a high humidity environment, HCN will quickly dissolve into the water in the air, and precipitate out as hydrocyanic acid. Until such time as either air pressure (which will be high in a closed, warm chamber), temperature or humidity or all three are reduced, (remember your Universal Gas Laws!) the HCN will remain in liquid form. This will dramatically increase the time it takes for the HCN to outgas from the Zyklon crystals, and the time needed to kill people - if they can be killed at all, the water in the bodies nearest the gas source will absorb the HCN, turning people into, as Rudolph has pointed out, biological gas filters. And, the higher the pressure, the more rareified the air, and the less gas that can be dissolved in it, reducing the dew point and creating more hydrocyanic acid.
Also - a thin pool of hydrocyanic acid would form on the floor just beneath the crystals. While HCN is a weak acid, nevertheless, it would eat away at the concrete on the floor, and create a visible staining pattern. If those introduction columns you hear so much about ever existed, the staining pattern would be in the outline of those columns, and that stain would still be visible today. The stains would also include some ferrocyanate and even common rust that would have dripped down from the iron in the wire introduction columns, which would not have been galvanized to make them acid proof.
The stain ain't there, is it? And, since hydrocyanic acid would not have been removed by any ventilation system - certainly not one working a crowded room full of dead bodies that are mainly water - when they opened the doors to the chamber, the drop in pressure, humidity and temperature means the pools of acid would have started conversion into gas, poisoning the workers. The more you go over the dynamics of what had to be, the less likely it becomes.