THE RUDOLF REPORT

vapor pressure HCN [atm]1.41.210.80.60.40.26. FORMATION AND STABILITY OF IRON BLUEboiling temperature00-10 -5 0 5 10 15 20 25 30 35Temperature [°C]approximately36% by volume.Condensation ofHCN on surroundingobjectswould occur onlyif the percentagerose over theequilibrium percentage(the socalleddew point).Since in all caseshere under consideration,a maximumconcentrationof 10% HCN in air would only be reached for a short period oftime close to the source of HCN (the Zyklon B carrier), no condensationof HCN on walls can be expected. An exception is, however, theso-called capillary condensation, which can occur in finely porous materialssuch as cement mortar. 324Hydrogen cyanide forms explosive mixtures with air in the rangeof 6 to 41% by volume. With strong initial ignition, its explosive effectscan be compared with nitro-glycerin. 325 In the applications underdiscussion here, a proportion of 6% by volume and more can bereached in the immediate vicinity of the source, which suffices for localblow ups at the most. Hence, only inappropriately high concentrationscan lead to explosive mixtures, as shown by a corresponding accidentin 1947. 16 With correct application quantities and concentrations,the technical literature indicates that there is practically no dangerof explosion. 326140120100Graph 1: Vapor pressure of hydrogen cyanide inpercentage of air pressure as a function oftemperature.80604020vapor pressure HCN [%]324 The lowered vapor pressure caused by adsorption effects in a narrow hollow space leads toearly condensation.325 The usual explosive in dynamite. Cf. Wilhelm Foerst (ed.), Ullmanns Encyklopädie der technischenChemie, vol. 5, Urban und Schwarzenberg, Munich 3 1954, p. 629.326 Willibald Schütz, “Explosionsgefährlichkeit gasförmiger Entwesungsmittel”, Reichsarbeitsblatt,Teil III (Arbeitsschutz no. 6), no. 17/18 (1943), pp. 198-207, here p. 201.157