THE RUDOLF REPORT

6. FORMATION AND STABILITY OF IRON BLUE200c(HCN) [mg/m²]15010050c(HCN) = 100 × e -t/0.3 + 100 × e -t/400 0.5 1 1.5 2 2.5 3 3.5 4 4.5time [days]Graph 8: Drop in the hydrogen cyanide concentration in old, dry, cementblocks, after 24-hour fumigation with 2.5% HCN by volume 409 (see footnotein Table 7, S. 187).This is only a correct description of the process when the concentrationof hydrogen cyanide in air in the room remains constant. Thefunction then reaches its maximum saturation after approximately 20days. In order to allow for such an approximation, one must reduce thegassing time involved in such a way as to equal real conditions withvariable concentrations. In case of a series of consecutive gassings andairings of masonry, a quasi-constant concentration will be reached after20 cycles as well.189