Holocaust denial often asserts that Zyklon B could not have been used for killing in the gas chambers, because it is explosive, and the furnaces were nearby.
They overlook, however the fact that the concentration of HCN necessary to cause death is nearly 200 times lower than that necessary to cause an explosion. Although the SS used a concentration higher than the lethal one, it was far less than what would be required to cause an explosion.
As a reference, one can look at “The Merck Index” and the “CRC handbook of Chemistry and Physics”, or consult any manual dealing with toxicity and flammability of chemicals. For HCN, a concentration of 300 ppm (parts per million) kills humans within a few minutes (Merck, 632, entry 4688), while the minimal concentration that can result in an explosion is 56,000 ppm.
Frank Deis provides the following information from Merck, with editorial comments in  brackets:
-Hydrocyanic acid;- “Blausaeure” (German). CHN; mol wt 27.03 … HCN. Prepd on a large scale by the catalytic oxidation of ammonia-methane mixtures [refs omitted]. May also be prepd by the catalytic decompn of formamide. Conveniently prepd in the laboratory by acidifying NaCN or K4[Fe(CN)6]. [Editor’s note: this last formula is quite similar to, but different from Prussian Blue, also a major topic in the
Leuchter Report. Prussian Blue is Ferric Ferrocyanide, or Ferric hexacyanoferrate (II). The formula is Fe4[Fe(CN)6]3. The =ferric= salt of ferrocyanide is insoluble in water. Other salts, such as the =potassium= salt of ferrocyanide, are quite soluble in water] [more refs omitted]
Colorless gas or liquid; characteristic odor; very weakly acid (does not redden litmus); burns in air with a blue flame; =intensely poisonous= even when mixed with air. d(gas) 0.941 (air = 1) [Editor’s note: notice, the gas is LIGHTER than air]; d(liq) 0.687. mp -13.4. bp 25.6 <[ latest defense of Leuchter made a big deal out of how the gas would condense out on the cold walls. This would clearly happen to some extent in a cold room. If the room were filled with people, the gas would stay warm] Miscible with water, alc; slightly sol in ether. LC50 [lethal concentration that kills 50% of test animals, NOTICE that this is dependent BOTH on time and on concentration!] in rats, mice, dogs: 544 ppm (5 min), 169 ppm (30 min), 300 ppm (15 min), [ref omitted].
Human toxicity: High concn produces tachypnea (causing increased intake of cyanide) [tachy = rapid, pnea = breathing] then dyspnea [dys = difficult, pnea = breathing] paralysis, unconsciousness, convulsions, and respiratory arrest. Headache, vertigo, nausea, and vomiting may occur with lesser concentrations. Chronic exposure over long periods may cause fatigue, weakness. Exposure to 150 ppm for 1/2 to 1 hr may endanger life. Death may result from a few min exposure to 300 ppm. Average fatal dose [ingested] 50 to 60 mg. =Antidote= Sodium nitrite and sodium thiosulfate.
Use: The compressed gas is used for exterminating rodents and insects and for killing insects on trees, etc. =Must be handled by specially trained experts.=
[end of article] (Merck, 632)
Cyanide is a small molecule. Basically it is toxic because it resembles the oxygen molecule, O2 or OO looks like HCN to the binding sites in the mitochondria and also probably to the heme groups in hemoglobin and myoglobin. If Cyanide “sits down” on the cytochrome a/a3 complex at the end of the mitochondrial respiratory chain, then the oxygen you breathe no longer does you any good. You can’t use it as an acceptor for high energy electrons, and you can’t make ATP by the usual method of oxidative phosphorylation. Your body makes you breathe faster at first, in an attempt to overcome it, and then cells start dying from lack of oxygen and lack of ATP energy.
In general, the statements about chemistry in Paul Grubach’s defense of the Leuchter report seem valid. ( JHR, V12, #4) The =premises= are of course open to question, or wrong. Yes, high concentrations of cyanide will cause formation of prussian blue on cold wet bricks that contain high levels of iron ions. But were the bricks really cold and wet? Was the air cold enough for the HCN to condense? Did “high concentrations” exist, given the relatively low concentrations required for killing human subjects, as opposed to insects?
Anyway, I hope this information proves useful. I teach Biochemistry at Rutgers University, and that’s where my information about cyanide toxicity comes from. The Merck Index is a standard reference book that probably every library has. Frank Deis ([email protected])