The Holocaust Historiography Project
Auschwitz, by J.-C. Pressac
In order to give a better understanding of the texts referring to Zyklon-B, the units used, the concentrations for disinfestation and its toxicity, here are some data concerning its principal active agent, HCN (hydrocyanic or prussic acid):
· Molecular weight. 27.
· Weight per liter: 1.20g
· 1% by volume represents 12g /m³
· 1g/m³ represents 0.083% by volume.
· 1% by volume represents 10,000ppm (parts per million).
· 1ppm represents 0.0012g/m³ or 1.2 mg /m³
· With air, it constitutes mixtures whose lower and upper limits of combustion are respectively 5.6 % (67.2g/m³) and 40% (480g/ m³).
· Olfactory threshold: 2 to 5ppm (2.4 to 12mg/m³).
· Maximum threshold used in work places: 10ppm (12mg/m³)
· Exposure without a mask to a content of 100 to 200ppm (120 to 240mg/m³ for 30 to 60 minutes may result in death. The lowest lethal dose known for man by inhalation: 120mg/m³ in one hour and 200mg/m³ in ten minutes.
· Immediately mortal concentration: 300mg/m³ or 0.3g/m³.
· A concentration equal to or greater than 12gm/m³ (1%) would not tolerable even for a man wearing a mask except in case of necessity and not for more than a minute
· A concentration of 24g/m³ (2%) may bring loss of consciousness in ten minutes for a man with a mask.
· Concentration used in homicidal gassing in Birkenau: 12g/m³ (1%), or 40 times the lethal (or mortal) dose.
Concentrations in g/m³ and contact times recommended in disinfestation:
· Mosquitos: 0.25 for 30 minutes.
· Bugs: 2.5 for 1 hour.
· Fleas: 125 for 2 hours.
· Lice: 5 for 2 hours.
· Cockroaches: 5 for 2 hours.
· Destruction of all insects: 5 for 6 hours.
· Rats and mice: 2.5 for 2 hours.
(Or according to Degesch: 2-4g/m³ for 4 hours).

Concentration used for disinfecting mills according to Degesch: 10g/m³ This level, close to 1%, does not prevent Degesch operators from distributing Zyklon-B disks with bare hands and apparently without ill effects [Photos 7 and 8].

A concentration of 15 to 30g/cm³ can be reached in restoration work (in the case of wooden works of art [statues] Infested by death watch beetles).
Faurisson has succeeded in his writings in presenting prussic acid as a dragon breathing fire, scarcely to be approached and with clawed feet clinging strongly to the ground even when dead. This apocalyptic picture has but little to do with actual practice. If HCN was like that, the staff of Degesch would long have been unemployed. After the world war, the Germans acquired greater experience than other nations in the handling of gases. Thus, they were the only people to have perfect mastery of the use of gas lighter than air (hydrogen) in their Zeppelin airships while the Americans who filled their airships with a non inflammable gas (helium) suffered one setback alter another. Just as the Hindenburg “accident” put an end to this supremacy and to the reign of lighter than air craft. the fraudulent use of Zyklon-B to exterminate Jews “stopped” the spread of gaseous disinfestation — although this technique is of incontestable value.
[Editorial note: Photo 13 is incorrectly labeled Photo 12 in the original publication.]
Photo 13 Photo 13: [PMO neg. no. 1196]

Label of a Degesch packing case for
Zyklon-B cans sent to Auschwitz on
24th April 1944. Guaranteed shelf-life:
three months from the date of dispatch.
Document 5: [which can be consulted inGerman at the Paris CDJC
under reference CLIX a21]
Office of Chief of Counsel for War Crimes
I. Properties of prussic acid (hydrocyanic acid)
Prussic acid is a gas which is generated by evaporation.
Boiling point 25 degrees Centigrade
Freezing point -15 degrees Centigrade
Specific gravity 0.69
Steam density 0.97 (Air 1.0)
The liquid evaporates easily
Liquid: Transparent, colourless
Smell: Peculiar, repulsively sweet
Extraordinarily great penetrative powers
Prussic acid is soluble in water
Danger of explosion
At 75 g prussic acid per m³ air. (Normal application approx. 8 10 g per m³, therefore
not explosive.)
Prussic acid may not be brought into contact with an open flame, glowing wires etc.,
because then burns up slowly and loses all its effectiveness (carbonic acid, water and
nitrogen are formed)
Toxic effects on warm blooded animals
Since prussic acid has practically no indicative irritant effect it is highly toxic and very
dangerous. Prussic acid is one of the most powerful poisons lmg per kg of body weight
is sufficient to kill a human being. Women and children are generally more susceptible
than men. Very small amounts of prussic acid do not harm the human body, even if
breathed continuously. Birds and fishes are particularly susceptible to prussic acid
Toxic effects on insects
The effects of prussic acid on insects do not depend on the temperature to the same
extent as that of other gases, that is, it is also effective at low temperatures (even at 5
degrees Cent.) The eggs of many insects, particularly of bugs and lice, are more
susceptible than the full grown insects.
Toxic effects on plants
The degree of toxicity depends on the type of vegetation on the plants. Plants with thick
leaves are less susceptible than those with thin ones. Mildew and dry rot are not killed
by prussic acid. Prussic acid does not destroy bacteria.
II Method of using prussic acid
ZYKLON is the absorption of a mixture of prussic acid and an irritant by a carrier.
Wood fiber discs, a reddish brown granular mass (Diagriess Dia gravel) or small
blue cubes (Erco) are used as carriers.
Apart from serving its purpose as an indicator, this irritant also has the advantage of
stimulating the respiration of insects. Prussic acid and the irritant are generated through
simple evaporation. Zyklon will keep for 3 months. Use damaged cans first. The
contents of a can must be used up at once. Liquid prussic acid damages polish,
lacquer, paint etc. Gaseous prussic acid is harmless. The toxicity of the prussic acid
remains unchanged by the addition of the irritant; the danger connected with it is
however considerably decreased
Zyklon can be rendered [harmless] by combustion.
III Possible poisoning
1. Slight poisoning

Dizziness headache, vomiting, general feeling of sickness, etc, All these symptoms pass
if one immediately gets out into the fresh air Alcohol reduces resistance to prussic acid
gassing, therefore do not drink alcohol before fumigation.

Prescribe 1 tablet Cardiazol or Veriazol in order to prevent heart disorders, if necessary
repeat after 2 3 hours.
2. Severe poisoning

The affected person will collapse suddenly and faint

First aid: fresh air, remove gas mask, loosen clothing, apply artificial respiration.
Lobelin, intramuscular 0.01g. Do not give camphor injections.
3. Poisoning through the skin

Symptoms as for 1. Treat in the same way.
4. Stomach poisoning

Treat with Lobelin intramuscular 0.01 g
Ferrous sulfate
Burnt magnesia.
IV Protection against gas

When fumigating with Zyklon use only special filters, e.g the filter insert “J” (blue
brown) of the Auergesellschaft Berlin or of the Draegewerke, Luebeck Should
gas seep through the mask, leave the building immediately and change filters after
also checking the mask and its fit to see whether they are tight