Kellex's design for the main process building of K-25 called for a four-story U-shaped structure long containing 51 main process buildings and 3purge cascade buildings. These were divided into nine sections. Within these were cells of six stages. The cells could be operated independently, or consecutively, within a section. Similarly, the sections could be operated separately or as part of a single cascade. When completed, there were 2,892 stages. The basement housed the auxiliary equipment, such as the transformers, switch gears, and air conditioning systems. The ground floor contained the cells. The third level contained the piping. The fourth floor was the operating floor, which contained the control room, and the hundreds of instrument panels. From here, the operators monitored the process. The first section was ready for test runs on 17 April 1944, although the barriers were not yet ready to be installed.