Jump over the water to the metal platform in the middle of this room. Swim through the pipe, and once you are at the end, turn right and climb on top of the ladder. You will immediately land on top of the welding equipment you are after. You can now move a manhole cover aside and drop into the manhole. Go through the door, drop down onto the platform next to the water, and use your LKW to cut through the metal plate in front of you. He is sitting in front of the door you wish to go through. Backtrack your steps into the safehouse, and at the ground floor, you will see the black guy that you met in camp Belica (he's the one that told you to swap uniforms so you could get in the prison block with Seth). He will tell you to retrieve some welding equipment for him that dropped into the water. He is in one of the helicopters in the back of the hangar.
Make your way to the hangar and talk to Fergus. Eventually, you will just wake up again, and there will be another health upgrade right next to your bed in the usual spot (1/1) Health Upgrade. Doing this changes how your campaign evolves at a later point throughout the story.
This time, you won't wake up right away, but you will trigger a cinematic in which you will train Tekla in the use of firearms. Go and find your own bed on the 1st floor, and as usual, take a nap.
