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Sector D is one of the seven main Sectors 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.
 Administration Center
The Administration Center is a large underground complex where the bureaucratic aspects of Black Mesa's upkeep take place along with some limited research. It is seen in the chapter Office Complex. The floors are mostly covered with black and white tiles placed in a checkerboard fashion, typical of the area. 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, during the Cold War era.
 High Security Materials Storage Area
The High Security Materials Storage Area is a large Cold War era storage facility above the Administration Center. It is seen in the chapter "We've Got Hostiles". As the military have just invaded the facility, many Sentry Guns and Laser Trip Mines have been installed, targeting civilians and alien creatures. Most areas are separated with heavy fire doors that will close when their emergency button is pressed.
 Silo D
Silo D is a large abandoned Cold War era missile silo that houses the Experimental Propulsion Laboratory used for testing rocket engines. It is seen in the chapter Blast Pit. It is connected to the High Security Materials Storage Area by an old decommissioned rail system. It houses three silos.
Silo D-01, Engine Testing (green-coded) is located in the middle of the silo. It is the largest and most important of the three. This is where the engines are actually tested. Three huge Tentacle creatures occupy the silo. The other two silos are directly connected to this silo, and can be only accessed through here.
Silo D-02, Power Facility (green-coded) provides energy to Silo D-01 and is accessed through the lowest door of the central chamber. Silo D-03, Wind Tunnel (yellow-coded) contains a huge propeller and is accessed from the upper door inside Silo D-01. The nearby Fuel Room contains the fuel and oxygen reserves provided for the Silo D-01 engines.
 Behind the scenes
According to the unused textures, the train hub in Sector E was originally part of Sector D.
 List of appearances
 Main games
The Portal Device
|Half-Life Alpha progression||Succeeded by|
The Security Complex
|Half-Life story arc journey||Succeeded by|
Sector E Materials Transport