"Hello, and welcome to the Black Mesa Hazard Course, where you'll be trained in the use of a Hazardous Environment Suit. I am your Holographic Assistant."
Encountered in all four of the original Half-Life games, Sector A's Training Facility contains the separate Hazard Courses used for training scientists (predominantly in the use of the HEV Suit in the standard "Black Mesa Hazard Course") and security guards (in the "Black Mesa Hazard Course for Security Guard Training").
Located right outside the Training Facility, it houses a large satellite uplink dish. This facility is used in the Decay chapter Surface Call when Colette Green and Gina Cross help Rosenberg contact the military.
As seen in the Security Shift Schedule given to Barney Calhoun, Sector A features an Area 4 Personnel Dormitories. Two security guards started their Red (from 09:00 to 22:00) and Orange (from 21:00 to 10:00) Shifts there on May 15, 200-.