The Leuchter FAQ: Disparities in Hydrocyanic Compound Levels

Holocaust deniers often claim that since more hydrocyanic compounds were found in the delousing chambers than in the ruins of the so-called “extermination” chambers at Auschwitz, and the reverse would be true if people were actually gassed there, it is clear that no gassings occurred.

But – HCN is far more effective on warm-blooded animals (including humans) than on insects, so the period of exposure to HCN is far longer for delousing clothes than that required for homicidal gassings, and a much lower concentration is necessary to kill people instead of insects.

A concentration of up to 16,000 ppm (parts per million) is sometimes used, with exposure times of up to 72 hours, to kill insects, but as little as 300 ppm will cause death in humans within fifteen minutes or so.

Breitman offers background information about the development of Zyklon B as a killing device, and provides clear evidence that the Nazis determined the effective Zyklon B concentration through a process of trial and error. (Get pub/camps/auschwitz/auschwitz.faq1)

When the difference in the concentration of gas required to kill insects and humans was mentioned in Leuchter’s cross-examination in the Zündel trial, Leuchter responded: ” I’ve never killed beetles. I, you know, I don’t know. I haven’t made computations for killing beetles” – Hardly the response one would expect from an “expert” on the subject…

Because of the relatively small concentrations required to exterminate humans as opposed to lice, and because of the far shorter exposure time required, the HCN in the gas chambers used to kill humans hardly had time to form chemical compounds on the walls.

The gas chambers were not very large (those in Kremas II and III were about 210 square meters), and the Zyklon B was dropped through four openings in the roof, spreading the gas very quickly. These openings are still visible in the ruins of the gas chambers, and rare photographs of them, taken while the camp was in operation, exist, and copies are readily available (Brugioni et al) from the sources noted in Section 6.1, below. Since the concentration used was higher than the lethal one, death was swift. (Get pub/holocaust/gifs/ krema4.gif – Krema IV was above-ground, and the Zyklon B was introduced through clearly visible slits in the walls. See also ~/gifs/ c_krema4.gif, which provides a closeup of the wall openings.


Leuchter‘s data is further suspect because the delousing chambers where he obtained his samples were left intact by the SS, while the extermination chambers were destroyed. Clearly, their walls were exposed to the elements for forty-five years, which would certainly effect the validity of the samples taken. (The ruins of Krema II are covered with about three feet of water during certain periods of the year, and HCN compounds would eventually dissolve under such conditions. Nonetheless, so many gassings occurred there that some of the compound did remain).

Summarizing, the walls of the extermination gas chambers were in contact with HCN for a much shorter time then those of the delousing chambers, and for the last 45 years were exposed to surroundings which dissolve the compounds, while the delousing rooms were not. Therefore it is obvious that less traces of compounds would remain in them. This debunks the major “amazing discovery” in Leuchter’s report, which, in retrospect, wasn’t ‘amazing’ at all.

This fact – that all, or most, of the compounds would vanish during 45 years of exposure – is quite clearly stated in the report written by the experts at the Cracow Institute of Forensic Research:

In the name of Prof. Dr. Jan Sehn, Krakow
Division of Forensic Toxicology

Krakow, 24 Sept. 1990
Westerplatte 9 / Code 31-033
Tel. 505-44, 592-24, 287-50
Telex 0325213 eksad …

The hydrocyanic acid (HCN) that is released from the Zyklon B
preparation is a liquid with a boiling point of about 27 degrees
Celsius. It has an acidic character, and therefore forms
compounds with metallic salts, which are known as cyanides. The
salts of alkaline metals (such as sodium and potassium) are
water soluble.

Hydrocyanic acid is a very weak acid, and accordingly its salts
dissolve easily in stronger acids. Even carbonic acid, which is
formed as a reaction of carbon dioxide with water, will dissolve

Stronger acids, such as sulfuric acids, easily dissolve the
cyanides. The compounds of cyanide ions with heavy metals are
longer lasting. This includes the already mentioned Prussian
blue, although this will also slowly dissolve in an acidic

Therefore, one can hardly assume that traces of cyanic compounds
could still be detected in construction materials (plaster,
brick) after 45 years, after being subjected to the weather and
the elements (rain, acid oxides, especially sulfuric and
nitrogen oxides). More reliable would be the analysis of wall
plaster [samples] from closed rooms which were not subject to
weather and the elements (including acid rain).

The discovery of hydrocyanic acid compounds in samples of
material which had been subject to the elements can only be

The deniers often claim that the gas chamber in Krema I was left intact, and therefore its walls were not exposed to the elements. Curiously, they also make great issue of the fact that Krema I was converted into an air-raid shelter, and then rebuilt by the Soviet Army, after the liberation of the camp, to reproduce its original shape, saying that it has been used to mislead the public, who were told that people were gassed in the building. (The logic of their holding both views when it seems advantageous to do so will perhaps escape you, but then logic has not been a demonstrated asset when it comes to Holocaust denial. See Section 3.0.)

The modification consisted of essentially removing some partitioning walls inside the gas chamber, which were added as a common feature of bomb shelters. Nontheless, this is the room in which people were gassed; there are still traces of cyanide on its walls, as Leuchter admits (he found traces in 6 of 7 samples).

But – the gas chamber of Krema I was used only for a short time, before the conversion. This, and the fact that “only” about ten thousand people were murdered within it, compared to three-hundred-fifty-thousand and four-hundred-thousand in Kremas II and III, explains why relatively small amounts of cyanide compounds remain. The other Kremas were destroyed by the SS prior to the Soviet liberation.

Finally, cyanide compounds were found on the ventilation grills of the extermination chambers, proving beyond doubt that gassing did take place within.