Anomalous Materials is the second chapter of Half-Life.
It is the sector of Black Mesa that Gordon Freeman works at. The early part of the game leading into the Resonance Cascade is spent here.
Anomalous Materials is composed partially of industrial materials (metal and lab equipment) and partially of domestic materials (tile and drop ceilings). Metal walls should be balanced with the concrete walls on the outer edges of the lab. The hallways have high ceilings, but not high enough for two full players on top of each other. Air ducts come out of walls and into others.
Lab equipment such as monitors and computers are common. There are occasional windows, as seen in the hallway leading towards the coolant reserve. Retinal scanners should be found near doors leading out of the sector to restrict access. Although it's a lab, break rooms should be found at least once a map containing a few tables, vending machines and trash cans.
The machinery in the facility should get denser as the player gets closer to the anti-mass spectrometer.
The main NPCs players should find here are scientists and security guards. Security guards should mainly be used to restrict access to areas where retinal scanners wouldn't make sense or to add variety. They are never found entirely idle.
Scientists can usually be found typing on computers or studying data on whiteboards. They may also be found in the break rooms tidying up.