LOL, I was checking the link on the Zyklon Discoids
booklet, and in skimming through it ...
I noticed that this source directly contradicts Pressac's notion that removing the warning agent for the Zyklon-B that was sold to the SS in wartime was a "criminal trace" for Nazi mass-murder because normal fumigation would never neglect this "important safety feature" (not even by the military during the war).
Here is what American Cyanamid (1938) says about "Warning Gases" on pages 26-27 in their fumigation literature:
American Cyanamid wrote:
It is readily admitted by all authorities that a perfect warning gas, that is, a gas which would warn under any and all conditions, would be highly desirable. However, the subject has been very thoroughly investigated by a number of industries and no warning gas has yet been used or proposed which does not introduce greater hazards, and unless a warning gas is wholly satisfactory it is not satisfactory at all.
One of the many difficulties in connection with warning gases is that they may air out either long before or long after the parent gas. If the former occurs, a false sense of security is created; if the latter, the process of aeration and time of turning the premises over to the tenants, is greatly delayed. [...]
The foregoing are, of course, unusual instances but they forcefully illustrate the unreliability of warning gases. [...]
Until the ideal warning gas is found, city regulations should not attempt to enforce the use of a warning gas but should be so drawn that the ordinary safety precautions which are necessary in all fumigating work, will be strictly observed.
It has been repeatedly demonstrated, that when sensible regulations are enacted and thereafter sensibly administered, fumigating work on a large scale can be carried on without accident.
Discoids do not contain a warning gas, but if specifically requested, will be supplied with a tear gas at an increase in price.