31. Door shafts may double as ventilation shafts to reduce the digging, although this is inadvisable. 32. White ducts are ventilation shafts for the underground areas. 33. Challis escapes through a ventilation shaft and rescues Ellie. 34. There were the " disinfectors " who poured the Zyklon-B crystals into the ventilation shafts . 35. It was therefore decided to sink a new ventilation shaft and work commenced in April 1913. 36. Their ventilation shafts were covered by metal ventilation louvers, coupled with spark arrestors and dust deflectors. 37. From 1871 steam tugs were used to pull boats through, and extra ventilation shafts were installed. 38. In many places the structure was designed to have ventilation shafts to allow some convection inside. 39. The group infiltrates the quarry and inserts JR into the ventilation shaft above the gold room. 40. Two ventilation shafts were provided to the tunnel.
