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Gas Detectors in the Auschwitz Crematorium II

by Arthur R. Butz

The extermination legend claims that the pesticide Zyklon B was used to exterminate Jews in a gas chamber within Auschwitz Crematorium II at Birkenau, specifically, in Leichenkeller 1 (morgue cellar 1), whose alleged real purpose was concealed by being so designated. Zyklon B works on the target pests by releasing hydrogen cyanide (HCN) gas by evaporation from the liquid form as retained in the otherwise inert pellets. It was widely used for delousing operations in the German concentration camp system and elsewhere.

In his 1989 book Pressac [1] remarked on a telegram of 26 Feb. 1943, from the Auschwitz construction department to the furnace maker Topf. At that date, the construction of Crematorium II was nearing completion. The telegram requested delivery of 10 gas detectors for Crematorium II, as had been earlier discussed. The specific gas to be detected was not stated but, by a process of tortured reasoning, Pressac concluded that the detectors were for HCN gas, rather than for the products of combustion, such as CO or CO2, in the furnace room, and classified this document as one of his so-called criminal traces. Robert Faurisson wrote, in reply, that Pressac himself had solved this problem, and that there was no reason to believe the detectors were for HCN [2].

Pressac did more research and published a new book in 1993, in which he produced a document newly discovered in the recently opened Moscow archives. It is a letter dated 2 March 1943, from the Topf company (by Senior Engineer Prüfer and a Topf colleague) to the Auschwitz construction department, and it shows that HCN was indeed the specific gas to be detected by the detectors. It reads:

We confirm receipt of your telegram specifying Immediately send 10 gas detectors as agreed, price quote to follow.

We hereby inform you that two weeks ago we inquired, of five different companies, concerning the residual HCN detection devices sought by you. We have received negative responses from 3 companies and 2 have not yet answered.

If (Wenn) we receive information on this matter, we shall immediately contact you, in order to put you in touch with a company that makes these devices.

Pressac remarked triumphantly [3] that This document constitutes the definitive proof of the existence of a homicidal gas chamber in Crematoium II.

Faurisson’s reply was that Zyklon B was used for delousing operations throughout the camp and of course in Crematorium II. Naturally HCN gas detectors would have been required in such operations, in which they are standard equipment [4].

A Problem

In both cases Faurisson gave the simple, obvious replies that I would have given under the circumstances. However I believe this interpretation is wrong, for reasons that may be seen by examining the document. The main obstacle to interpreting this letter in terms of Zyklon B is the roles of Topf and Prüfer.

Zyklon was a product of the DEGESCH company; Zyklon and associated equipment such as gas detectors and gas mask filters were also manufactured by other companies such as Tesch & Stabenow and Drägerwerke. At Auschwitz delousing operations with Zyklon were such major and continuous tasks that there existed there a special department, the Referat für Schädlingsbekämpfung (Pest Control Office), that conducted them. This department on occasion even communicated directly with DEGESCH [5].

Topf was a furnace maker with crematorium ovens as a sideline, and was the principal civilian contractor in the construction of crematoria at Auschwitz. Prüfer was the main Topf contact of the Auschwitz construction department and of course was not associated with the special SS delousing squads that regularly worked with the Zyklon. Why should Prüfer have been searching, indeed with great difficulty, for devices that were standard equipment for the delousing squads, and were readily available from the DEGESCH and other companies, which had developed and supplied Zyklon? The standard DEGESCH detector for HCN required exposing a test paper and observing the color assumed. The Prüfer letter even implies that he does not know whether the desired devices exist, was confronting this specific need for the first time, and does not know very much about it, inferences that are very important in interpreting the letter. I do not believe the letter had anything to do with Zyklon.

There may however have been one connection between Topf and Zyklon. Robert Faurisson has brought to my attention an anti-revisionist, Pressac supporting book published in France in early 1997. A footnote declares: [6]

The study of the history of the Topf and Sons company of Erfurt would be essential to show the progression to mass crime. Topf made, in the Twenties, crematoria but also grain silos. In the after sale services and maintenance for these silos, Topf also involved itself in HCN disinfection and furnished all necessary material. Thus the two branches of activity of the firm converge in a striking manner toward the crematoria — gas chambers of Birkenau. On this particular sort of study, the works of Pressac are of the greatest utility and it is in this way that they should be used.

The author gives no sources but I think the claim of such Topf involvement with HCN, presumably via Zyklon, is quite plausible. Under conditions where Topf would have been the only company that a farmer dealt with in constructing his silo, it would have been natural for Topf to serve as retailer of supporting materials and equipment made by DEGESCH and other companies. However such a Topf role had no bearing on conditions at Auschwitz in 1941 — 1945, where a special department regularly conducted operations with Zyklon. Their personnel would have been responsible for declaring when a treated facility was again safe to use. Is it plausible that Prüfer could have been involved in this when, as his letter shows, he didn’t know very much about it?

There remains one possibility. Perhaps some unusual feature of the cremation process, not understood by the Zyklon delousing personnel, raised a novel problem with the Zyklon that Prüfer was asked to solve. I can’t imagine such a feature, since cremation with coke seems basically like any other use of coke. However if such an unusual feature existed, would it not have come up earlier in the six muffle crematorium, also supplied by Topf, that existed in the Stammlager or Auschwitz I? In 1942 this sole crematorium was working at capacity, and the disastrous typhus epidemics were being fought with Zyklon. However the February — March 1943 correspondence marked the first confrontation of Prüfer with the problem involved. Some novel feature of Crematorium II had to be the problem.

It is also clear that the letter has nothing to do with gas detectors as defenses against chemical warfare. The German chemical warfare services were highly competent and organized, and would not have sent a furnace maker on a quest for such equipment.

From one point of view the problem raised has little to do with the extermination allegations. If the Zyklon were being used to kill people, rather than lice, then presumably the same specially trained squads would have been used or at least consulted, and the usual HCN gas detectors would have been used in the last stages of gassing operations. There would have been no problems in acquiring such standard equipment. Those who believe Zyklon was used for homicidal purposes should be as puzzled by this document as I was.

From another point of view this problem is very relevant to the claim of extermination, as explained below.

An Alternative Interpretation

The Topf letter of 2 March 1943 is strange and for a while I suspected its authenticity. However I have found an interpretation which may be correct and the main purpose of this article is to propose it. After I have done that I shall return to the question of the relevance of this problem to the extermination allegations.

HCN is of course a compound of hydrogen, carbon, and nitrogen and may be generated whenever materials containing these elements are burned. For example the fuel used for the crematorium ovens was coke and it is well known that HCN gas is a possible by-product in the process of making coke from coal. However there is apparently no danger of HCN release when coke, of whatever grade, is burned as a fuel; otherwise it would not be in such common use. HCN gas could not have been thus generated in the crematorium.

A remaining possibility is that HCN release was possible in the waste incinerator, which shared the chimney with the cremation ovens. Many materials may release HCN when burned. Among these are many fabrics, a highly relevant observation because the waste incinerator was most likely used to incinerate used camp fabrics (e.g. inmate uniforms and bed linen and mattresses). For example, silk and wool can release HCN when burned, a fact that has been known since the Thirties.

(image of flues and ducts)
Fig. 1. Arrangement of flues and ducts for Auschwitz Crematorium II.

As shown in Fig. 1, the chimney of Crematorium II was divided into three ducts. Six furnaces used this chimney, namely the waste incinerator and the five cremation furnaces (each with three muffles). The waste incinerator was on the opposite side of the chimney in relation to the cremation furnaces. These six furnaces used the three ducts on the basis of two per duct; thus the waste incinerator shared one of the three ducts with one of the cremation furnaces (the flues leading from the furnaces to the chimney were underground). The waste incinerator was also supplied by Topf, and it could have been Prüfer’s responsibility to take into account any HCN danger arising from it. Also, a gas detector differing from that used in the Zyklon delousing operations would seem fitting; perhaps a detector generating an audible alarm was desired [17].

While a concern for HCN release in combustion is routine today, it would have been novel in 1943, a fact that could explain the novelty, for Prüfer, of the desire for an HCN detector. Another thing that could account for this novelty is that the waste incinerator design was itself novel. I have no expertise in the field but, intuitively, I would think that a waste incinerator design sharing a chimney with other equipment, at which people are working, is dangerous.

The question of the quantities of HCN released in the burning of materials is complicated and depends on the chemical nature of the material, temperature, oxygen availability, and burning time. Since HCN is itself combustible, it makes a difference whether the combustion is static or dynamic, an example of the latter being when there is forced air blowing and the HCN is swept away from the hot zone before it can itself be decomposed in any way. However, HCN can be released under either condition. Another complication is that HCN can be released in the smoldering after a fire has been extinguished [8].

The term residual that appears in the letter in question could apply to either released HCN that, ideally, would have been consumed during the incineration process but wasn’t, or to HCN released after incineration, during smoldering. The chimney of Crematorium II used, as of 29 January 1943, a forced draft system based on suction but on 25 March 1943 Topf ordered this system removed due to overheating of its motors [9].

In October 1997 Carlo Mattogno released his own thoughts on the Topf — Auschwitz correspondence on HCN gas detectors. This article is available in English translation, in the original Italian and in German translation.

Mattogno did a rather better job, than I have done here, of showing that the exchange of letters could not have had anything to do with Zyklon. He gave reasons similar to those given here, but with much more documentary support. Unfortunately he implicitly equated Zyklon with HCN in his reasoning, and drew his conclusions believing he had shown that the exchange could not have had to do with HCN. Thus he concluded that the Prüfer letter of 2 March 1943 is a forgery, a possibility that I had once considered myself but have rejected. Mattogno had also expressed doubts about the authenticity of the letter with brief remarks in his book Auschwitz: The End of a Legend (published by the Institute for Historical Review, 1994).

A Specific Possibility

It remains to suggest a specific potential source for HCN development in the waste incinerator. In wartime Germany many articles had to be ersatz (artificial or synthetic), because of shortages of materials normally imported. Cotton was in very short supply and little was used for fabrics. Wool was available but not in normal quantities. In fact Germany relied heavily on the manufacture of rayon, and during the war army uniforms contained as much as 65% rayon. One must assume concentration camp uniforms, and other fabrics used in the camps, had high rayon content. Could the incineration of such rayon have produced HCN gas? It may seem not, because rayon has no nitrogen in its chemical composition. In making these statements, I am using the word rayon in the normally accepted sense; rayon is regenerated cellulose made from natural cellulose extracted from materials such as cotton linters or wood pulp. Cotton was scarce in wartime Germany so almost all rayon was made from wood pulp [10].

The burning of rayon can generate HCN gas if the rayon is impregnated with, but not chemically bound to, compounds of ammonia, which supply the necessary nitrogen. This was established some years ago by T. Morikawa, who conducted experiments that established that ammonia and its compounds, combined with cellulosic materials, can indeed result in the evolution of HCN when burned. The general conclusion was that such evolution was about the same as for substances having nitrogen in their chemical compositions in comparable amounts [11]. It is of great relevance, for this discussion, that Morikawa’s study of this point was motivated by the fact that ammonium compounds are added to many fabrics to make them flame retardant (this is sometimes called fireproofing, but that cannot be done literally with ordinary fabrics). Thus Morikawa’s experiments used, as the source of nitrogen, diammonium phosphate, a common flame retardant for fabrics.

During World War II diammonium phosphate was commonly used in Germany to make fabrics, particularly rayon, flame retardant. Two such products were marketed by I.G. Farben under the trade names Akaustan N and Akaustan N 1139. Another product, Akaustan K, used other ammonium compounds as the flame retardant [12]. A disadvantage of such flame retardants is that they are water soluble and gradually leach out when the fabrics are washed. Thus such soluble flame retardants are applied with the idea of periodic reprocessing in order to maintain the desired properties (by) simple immersion in aqueous solutions of the retardant [13]. That is, washing is followed by immersion in a solution of the flame retardant substance, then drying out. Another defense against leaching, employed by the Germans, used sulfamide (strictly speaking sulfuryl amide, SO2(NH2)2) in conjunction with a standard waterproofing agent, thus making reprocessing unnecessary [14]. Sulfamide is obtained by treating sulfuryl chloride with ammonia and one gets the impression from Morikawa that one could also expect evolution of HCN in burning of cellulose impregnated with it.

While I do not have a document that says so, I consider it very plausible that many concentration camp fabrics were treated with flame retardants for security reasons, i.e. to limit the effects of fires started by inmates. This would have been particularly the case with bed linens and mattress fillings. Thus I am proposing the possibility that fabrics used in the camps, destined to be disposed of by incineration, were known to present a danger of evolution of HCN in such incineration.

The favored German process for rayon manufacture was the viscose, which is also the favored process today. However two German factories used the older and simpler cuprammonium process. That the cuprammonium process involved a solution of ammonia does not appear relevant to the present problem. What may be relevant is that a price of its simplicity was that the cuprammonium process required celluloses of a high degree of purity. Thus cotton linters were considered the standard cellulose source for cuprammonium rayon but, on account of wartime shortages, the two German cuprammonium factories used wood pulp instead. This resulted in an inferior quality rayon. Much of the cuprammonium rayon was used for army uniforms, but there were other uses, for example military upholstery, mattress fillings, and parachutes. I have no source saying that it was used in concentration camp fabrics but, in view of its inferior quality, this is a very admissible conjecture. One version of the cuprammonium rayon used for mattress fillings was impregnated with urea and formaldehyde, with ammonium nitrate as a catalyst, in order to impart springiness to it [15]. It is known that urea can cause some ammonium based flame retardants to react with cellulose, thus giving a fabric so treated resistance to leaching [16].


In summary I am saying

  • It is certain the Topf letter has nothing to do with Zyklon.
  • It is almost certain that the HCN danger referred to arose from the waste incinerator. I would be astonished if it were shown that such was not the case.
  • It is probable that the HCN detectors were wanted because of a potential danger of HCN development in the incineration of fabrics, particularly rayons treated with flame retardants. However I am far from certain on this, and I will not be astonished if other materials, consumed in the waste incinerator, were shown to have been suspected by the Auschwitz management as potential sources of HCN development.


Above I promised to return to the question of the relevance of the problem treated here to the extermination allegations. The mass of documents shows that Auschwitz was a large concentration camp with a disastrous death rate, due mainly to typhus carried by lice. In response to such problems, the Germans made great use of the pesticide Zyklon B and constructed large crematoria. There are no records showing that Jews were gassed or exterminated. That is clear and it ought not be necessary to argue that such was not the case. The documentation is immense, and the physical facts concerning the camp are conclusive. For more detail, see the discussions of the death rates and the crematoria capacities.

Another approach uses the normal historical method; you study what the people of the time were doing. Elsewhere I have discussed the trap that the historian Walter Laqueur got himself into by applying this normal historical method to Auschwitz.

For practical purposes, the entire extermination legend rests on the claim that Auschwitz was an extermination camp where about a million Jews were gassed with Zyklon B in otherwise designated rooms within the crematorium buildings. Since that is emphatically not what the historical record says the promoters of the legend are highly selective in choosing documents, which Pressac calls criminal traces which, it is claimed, prove their thesis. The HCN gas detectors are one of the criminal traces on Pressac’s pathetically short list [17].

In historiography there is an alternative, and more commonplace, description of Pressac’s procedure with criminal traces. It is bad historiography of the simplest sort: tendentious selection of a very small part of the data, resulting in grossly distorted history.

Normally one cannot get away with this. But today a Pressac, waving aside historical reasoning and the mountain of documentary evidence, comes rushing forward waving some document and saying, in effect, but how about this?, and he is respected instead of being ignored or laughed at [18]. He is credited by some with finally proving the extermination allegation as it relates to Auschwitz, although it had for years been claimed that it had been proven and that there was nothing to argue about.

Thus to the person who objects that here I have treated petty details incommensurate with the scale of the historical claim involved I reply: you are right but it isn’t my fault! Ordinary historical reasoning observes that nobody acted, during the war, as though extermination was going on, and that the Jews were still there at war’s end [19]. However a lot of influential people won’t accept ordinary historical reasoning and the debate, to the extent that it exists, has revolved around the petty details.

The promoters of the legend may get away with such practices, for a while, in arguing the reality of physical exterminations of Jews during World War II. There are two leading reasons for this. Most obvious is the fact of the entrenched status of the legend. What ought to require proof has been allowed to flourish unproved, and the revisionists have in effect been forced to try to argue a negative. Another reason, less obvious but very simple, is that the revisionists may not be able to immediately offer correct replies to the sallies of the defenders of the legend. This appears to me to have been the case with the Topf letter. I don’t believe Faurisson’s immediate replies (which I would also have made) were correct. In fact nobody could be relied on to be correct under the circumstances and in the time frame involved. A comparison: there is much building activity at Northwestern University now. Does anybody believe that, fifty years from now, perhaps after some cataclysm, anybody could reliably interpret individual documents that were records of this construction? Of course not. Nobody could do that, and nobody could infallibly interpret every Auschwitz document from the period 1941-1945. Indeed, the hypothesis I have advanced here may be wrong, even though I have had a few years to consider the solitary document in question.

Some years ago I warned of these dangers [20]. It is not out of the question that, some day, an authentic Auschwitz document might utterly confound the revisionists, i.e. raise some apparently relevant question of detail which they will be unable to answer. I can only urge that the context, that is, the massive documentation and historical circumstance supporting the revisionist position, be kept in mind in the event of such a development.


  1. J.-C. Pressac, Auschwitz: Technique and Operation of the Gas Chambers, Beate Klarsfeld Foundation, NY, 1989, pp. 371, 432f.. The reader should understand that the title of this book is misleading, as the only real gas chambers whose technique and operation are discussed are fumigation gas chambers. The homicidal gas chambers are only imagined, based on alleged criminal traces. It is common to refer to this book in discussion of Auschwitz because it is the greatest single published source of reproductions of original documents and photographs for the camp.
  2. R. Faurisson, Auschwitz: Technique and Operation of the Gas Chambers, Journal of Historical Review, vol. 11, no. 1, Spring 1991, p. 59.
  3. Jean-Claude Pressac, Les Crématoires d'Auschwitz: La Machinerie du Meurtre de Masse, CNRS Éditions, Paris, 1993, p. 72 and Document 28. The document is also reproduced, together with an English translation, by J.-C. Pressac and Robert-Jan Van Pelt in their article in Anatomy of the Auschwitz Death Camp, Y. Gutman and M. Berenbaum, eds., Indiana Univ. Press, Bloomington, 1994, pp. 230f.
  4. R. Faurisson, Jean-Claude Pressac’s New Auschwitz Book, Journal of Historical Review, vol. 14, no. 1, Jan./Feb. 1994, p. 23.
  5. Raul Hilberg, The Destruction of the European Jews, p. 571 in the 1961 Quadrangle edition; vol. 3, p. 892 in the 1985 Holmes & Meier edition. Hilberg cites a letter from the Referat to DEGESCH.
  6. Jean-François Forges, Éduquer contre Auschwitz, ESF, Paris,1997, p. 28.
  7. Pressac (1989), pp. 284-287 (drawings of 23 Jan. 1942, on which Fig. 1 is based); pp. 306-312 (drawings of 19 March 1943, showing the same duct arrangement as in earlier drawings). Pressac (1989), p. 288 also reproduces a profile drawing for this arrangement; this profile drawing is also reproduced by Danuta Czech, Auschwitz Chronicle 1939-1945, Henry Holt, NY, 1990, p. 193. The Ofen is a cremation oven; if the reader uses a magnifying glass and squints hard the badly lettered word Müllverbrennungsofen (waste incinerator) can be seen. Pressac (1989), p. 217, on Topf waste incinerator role.
  8. Bryan Ballantyne, Hydrogen cyanide as a product of combustion and a factor in morbidity and mortality from fires, in Clinical and Experimental Toxicology of Cyanides, Bryan Ballantyne & Timothy C. Marrs, eds., Wright, Bristol, 1987, pp. 248-291. Yoshio Tsuchiya, Significance of HCN generation in fire gas toxicity, Journal of Combustion Toxicology, vol. 4, August 1977, pp. 271-282.
  9. Pressac (1989), pp. 214, 230, 306-310, 488. Pressac and Van Pelt (1994), pp. 232f.
  10. A.R. Urquhart, The German Rayon Industry During the Period 1939-1945, H.M. Stationery Office, London, 1952, pp. 13-16,275. This work was no. 33 in a series of British postwar studies of intelligence objectives.
  11. Tokio Morikawa, Evolution of hydrogen cyanide during combustion and pyrolysis, Journal of Combustion Toxicology, vol. 5, pp. 315-330, August 1978.
  12. Urquhart (1952), p. 272.
  13. Robert W. Little, Flameproofing Textile Fabrics, Reinhold, NY, 1947, pp. 167-170.
  14. Urquhart (1952), p. 272.
  15. Urquhart (1952), pp. 15ff, 28, 150-159, 273ff.
  16. McGraw-Hill Encyclopedia of Science and Technology, 7th edition (1992), vol. 7, pp. 139f (article on Flameproofing).
  17. Pressac (1989), pp. 432-457.
  18. On Pressac’s 1989 book see e.g. the NY Times, 18 Dec. 1989. On his 1993 book, which reproduced the Topf letter in question here, see (all 1993) l'Express, 23 Sept. pp. 76-87; Libération, 24 Sept. pp. 28f; Le Monde, 26-27 Sept. p. 7; Die Welt, 27 Sept. p. 1; AP report in the Denver Post, 2 Oct. p. 6A; Die Woche, 7 Oct. p. 8; NY Times, 28 Oct. p. A3 and 31 Oct. sec. 4, p. 2 and 8 Nov. p. A14; Chicago Tribune, 28 Nov. sec. 1, p. 25 and 13 Dec. sec. 5, p. 1.
  19. For some Jewish demography see Chapters I and VII of my book The Hoax of the Twentieth Century. Much more is to be found in Walter Sanning, The Dissolution of Eastern European Jewry, IHR, 1983. Both books are available from IHR.
  20. A.R. Butz, Context and Perspective in the 'Holocaust' Controversy, Journal of Historical Review, vol. 3, no. 4, Winter 1982, pp. 371-405.

Created: 4 March 1997
Last modified: 24 March 1998

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