Once More: "The Efficiency of Prussic Acid
at Low Temperatures".

By R. Irmscher.
German Society for Pest Control, Frankfurt am Main

This paper by Irmscher is the third technical report hosted by The Holocaust History Project on the evaporation of poison gas from its source material.

That gas is hydrogen cyanide (prussic acid) and its source material is the infamous Zyklon-B. The poison was used for delousing before it was adopted as the murder weapon in the Auschwitz gas chambers, and it is for delousing purposes that these three papers were written. The papers are relevant because they help us refute the claims of Holocaust-deniers regarding the evaporation of hydrogen cyanide.

This paper and the 1941 paper by Peters and Rasch contrast with the 1933 monograph by Peters in that they studied the speed of evaporation of HCN at lower temperatures. At lower temperatures the rate of evaporation slows, but both of these latter studies show that it does not slow so much as to make delousing impractical.

The Irmscher study differs from that of Peters and Rasch in that they studied not only a colder range of temperatures, but also looked at two different solid supports: cardboard disks and Erco. Erco is a gypsum (CaSO42-) product. The results from the Irmscher paper agree more or less with the earlier work of Peters and Rasch. The small discrepancies are probably due to a difference in the support used, or a difference in humidity - Irmscher affirms that humidity affects the rate of evaporation.

This paper puts to rest denier arguments concerning evaporation. It has been shown on the basis of this paper that rapidly lethal concentrations of HCN can build up in an matter of minutes, even using a low estimate of how much Zyklon was added to the gas chambers. This also helps show that the purported ventilation problem is overstated. The concentration of HCN that would build up in the gas chambers is small enough to require only a 20-100 fold dilution to reach a tolerable 40-50 ppmv, a concentration at which the Sonderkommando could enter the chambers even without gas masks. The solid support, along with the unevaporated HCN, could be removed to outgas safely elsewhere.

Please note that this paper contains two possible errors, which we have reproduced as they were printed. The captions on the data in the tables on p. 36 seem to be the reverse of those in the plots. One or the other is mistaken; we believe it is the cardboard disks which outgas more slowly and we are seeking further confirmation. Also, the orphaned footnote "*)" on that same page probably is the source for the curve on diagram 2 on p. 37. This inference is consistent with the actual contents of the Porter and Perry paper.