The first gassings at Auschwitz took place in early September 1941, when around 850 inmates—Soviet prisoners of war and sick Polish inmates—were killed with Zyklon B in the basement of block 11 in Auschwitz I. The building proved unsuitable, so gassings were conducted instead in crematorium I, also in Auschwitz I, which operated until December 1942. There, more than 700 victims could be killed at once. Tens of thousands were killed in crematorium I. To keep the victims calm, they were told they were to undergo disinfection and de-lousing; they were ordered to undress outside, then were locked in the building and gassed. After its decommissioning as a gas chamber, the building was converted to a storage facility and later served as an SS air raid shelter. The gas chamber and crematorium were reconstructed after the war. Dwork and van Pelt write that a chimney was recreated; four openings in the roof were installed to show where the Zyklon B had entered; and two of the three furnaces were rebuilt with the original components.