Sector D Administration is one of the seven main of the Black Mesa Research Facility. Appearing only in Half-Life, it is covered by three chapters: Office Complex, "We've Got Hostiles," and Blast Pit. It is connected to the Yellow Line of the Black Mesa Transit System. As suggested by the name of several texture files used in the area, many parts of Sector D, notably the Administration Center, were built in the 1950s.