The building ventilation fan room was located to the south of the valve pit. Here were located the main blowers, heaters, and air filters for the entire building’s heating and ventilation systems. There were two dual-drive (steam and electric) supply fans and four exhaust fans (two steam and two electric). The exhaust fans were located in separate concrete cubicles to isolate them from the supply system. A concrete enclosed exhaust duct ran from the fan room to the 200 ft high stack, and exhausted the air from the 105 building.