Let's get straight to the point. The Chemical Plant door code is 8506. This code remains the same in every playthrough, allowing you to enter it right away using our guide.
Accessing the locked room will reward you with the Zubr-19 submachine gun and a PDA.
The Chemical Plant code door is inside the building, on the very bottom floor, where you'll also meet the local doctor, Dr. Burakhovsky.
If you can't explore the entire Chemical Plant (you haven't progressed far enough in the storyline) to gain access, you can jump over the fence in the northern part of the Chemical Plant. Just stand on the highest part of the embankment and time your jump.
The action game also received a content update.