The Declassified Mission Skull ahead will make the toxic fumes in this section affect your vision. Once activated, your screen will become blurry and hazy.
Take cover and move around the lab to encircle the enemies and take them out. More enemy reinforcements will appear from the control room ahead so dig in and clear them out. There's a Gnasher Sentinel auto-turret in the left side of the lab equipment in the middle of the room. Deploy it to have extra firepower.
Enter the control room and pick up the COG tag in the corner of the far side of the room.
Continue to the next lab to find the beacon. Activate the lever to power up the beacon and simply head to the door to complete the section.