Eventually you will arrive in Alpha Labs section four of the Alpha Labs chain of levels. At one point in this level, you will go through a door and enter a room with a control panel overlooking some sort of chamber with orange walls. There will be a scientist trapped inside.
Before you do anything however, make a manual save before you choose either of the following options. Now you will want to choose “Activate Chamber” from the screen’s menu instead of “Open Chamber.”
Once you get the achievement, LOAD the file you just made. Proceed down to where he was because there are collectables that you will miss.
Here is a video to show you the exact location (this video was made by runtstain100):