The architecture is largely the same as the previous chapter, although in far greater disrepair. Doors should be ajar and test equipment should be in pieces, especially around the spectrometer. As the player gets closer to the coolant reserve, the facility should be slightly less damaged and most machinery should not be in pieces.
Players should feel an acute sense of danger. Lighting and unexpected explosions create a large portion of the atmosphere in Valve's default maps. Only the equipment needed to progress, such as lifts, should be functional or equipped with an emergency service ladder for the player to use.
As in the previous chapter, scientists and security guards should be found, albeit scattered. Dead scientists and blood decals are also common, but should be proportional to the number of scientists found in the last chapter.
The first of the aliens are found here. Headcrabs should be found popping out of vents early on. Vortigaunts and bullsquids should be placed later and sparingly. Zombies should also be placed sparingly and less often as the player gets through the level.