Sepp Dietrich -- I'll give you my understanding of how the system worked; other readers may have corrections, comments, or changes to add.
As a technical matter, there are two steps to homicidal gassings, once the victims are in the gas chamber. The first involves killing them, and the second involves the subsequent clean-up.
The Zyklon-B came in pellets ("the carrier") soaked in prussic acid. To use the Zyklon-B, the pellets were exposed to the surrounding air, which caused the prussic acid to volatilize off the carrier and become a gas. To achieve homicidal concentrations for people or insecticidal concentrations for insects, it was necessary to seal off the area to be gassed while the gassing took place.
Once the gassing had taken place, the gassed area had to be aired out before it was safe for human activity again. Where the Zyklon-B was used to kill insects, this process involved natural ventilation -- opening the doors, windows, flues and ventilator shafts of the fumigated building and letting the gas dissipate in the air around the building.
This gets us to your first and second questions:
This may be a stupid question, but I'll ask anyway: 1) Where was the gas pulled to? Outside the camp via some sort of piping? Via a chimney where it dissipated in the higher air?
If indeed ducts of a non-mechanical nature were operated to extract the poison, the method of propulsion away from the surrounding area would not be sufficient enough to take it away from the Germans themselves, placing them also at risk. Would this be a correct presupposition? Or am I totally missing the mark here?)
The answer to your first question is that the gas was pulled to the area outside the building where the gassing took place. See section XI of the Zyklon-B handing instructions at http://forum.axishistory.com/viewtopic. ... 353#424353
. Note that this approach involves natural ventilation rather than mechanical ventilation, and discusses precautions to be used when the windows in the gassed building are open -- namely, the guards or working personnel should stand upwind when the structure is being aired out.
The handling instructions answer your second question about non-mechanical ventilation. Since the Zyklon-B gas was lighter than air, it would mix with and dissipate in the higher air as it rose. If there was a wind blowing through the open windows of the building which was gassed, the dissipating Zyklon-B might pose a threat to those standing too close to the ground floor windows on the downwind side of the building. If the gassed building had a basement, there might also be a problem for those standing too close to the basement's vents or windows. The handling instructions describe the necessary precautions for these potential problems.
In the homicidal gas chambers, mechanical ventilation was also used, which cut the time necessary to air out the chamber. This gets us to your additional question:
2) Forgot to ask; the ventilators, were they powered by fans and such?
That's the suggestion I got from the statements of Nyiszli ("Twenty minutes later, the electric ventilators were set going in order to evacuate the gas.") and Hoess ("The door was opened half an hour after the introduction of the gas, and the ventilation switched on."). See Pressac, pp. 473, 475.
Your third question was:
3) How long would Zyklon need to disperse if one merely kept the door open with a weaker draft coming in? How long with other natural types of ventilation? With mechanised? NB: I am aware that Pressac claims for 15 mins with proper ventilation.
However, we see Nyiszli stating that the gas lingered on for at least two hours. Who is correct?
I think the answer to the first part of the questions would depend on a number of variables, such as the concentration of gas, the size of the structure, the amount and efficiency of natural ventilation available, and the exhaust power of any mechanical ventilation which was used.
For the second part of this question, Nyiszli is talking about pockets of gas which had been trapped:
"The ventilators, patented “Exhator” system quickly evacuated the gas from the room, but in the crannies between the dead and the cracks of the doors small pockets of it always remained. Even two hours later it caused a suffocating cough."
and the irritant which caused the cough and which had been added to the Zyklon-B as a handling precaution to prevent inadvertent exposure to the volatilized prussic acid. See Section II of the handling instructions at http://forum.axishistory.com/viewtopic. ... 345#424345
Without knowing more about the properties of the irritant in Zyklon-B, and whether it mimicked or was different from the properties of the lethal volatilized prussic acid gas, I can't say whether the irritant might have lingered after the Zyklon-B gas had dissipated. It may also be that Pressac is talking about lethal concentrations of the Zyklon-B gas, as opposed to small trapped pockets containing the irritant which would cause members of the Sonderkommando to cough, but wouldn't kill them or significantly impede their corpse-hauling work
Your fourth set of questions was:
4) When natural extraction methods were utilised, were there coverings for the ducts? How big were the ducts? If there were no covers, would this not have caused problems for the potency of the chemical agent?
As best I can recall, natural extraction methods were only used in the first gassing experiments with Zyklon-B, because it took too long to air out the gas chamber. Some of the problems with natural extraction are mentioned in the Zyklon-B handling instructions for disinfestation purposes, specifically sections VII through XIV.
Your fifth question was:
5) The much famed “Prussian Blue” effect on the walls. Could the fresh air pumped in (or otherwise) have either prevented (in cases) or lessened such a marked effect on the walls?
I haven't seen any experiments which establish, or even discuss, the factors of gas concentration or structural compositions of the walls which affect the formation of prussian blue stains. Because the gas chambers were hosed out immediately after homicidal gassings:
The Sonderkommando squad, outfitted with large rubber boots, lined up round the hill of bodies and flooded it with powerful jets of water. This was necessary because the final act of those who die by drowning or by gas in an involuntary defecation. Each body was befouled and had to be washed. Once the “bathing” of the dead was finished — a job the Sonderkommando carried out by a voluntary act of impersonalization and in a state of profound distress — the separation of the welter of bodies began. (Nyiszli's description, at Pressac p. 473)
and the prussic acid gas was soluble in water (Zyklon-B handling instructions, Section I and Section XIII, paragraph 1), the washing process probably had more of an inhibiting effect on the formation of prussian blue stains than the mechanical ventilation.
Your eighth set of questions was:
8) I have seen references to a gas detector (eg):
After verifying by means of a gas detector that there was no longer any danger of hydrocyanic acid intoxication outside the gas chamber, operations would have resumed their “normal” course.
(Pressac, p. 377)
What sort of device did this look like? Was it handheld? Did it run through the wall into a system of dials displaying “SAFE”, for example?
I don't know what kind of detectors were used in the homicidal gas chambers, but the Zyklon-B handing sheet suggests that the gas detectors used in disinfestation operations were of the hand-held "litmus paper" type. See Sections XII and XIV(5) of the handling instructions at http://forum.axishistory.com/viewtopic. ... 353#424353
I'll try to answer your sets of questions 6-7 and 9 when I have a little more time.