Make your way through the water and up the stairs. You'll notice a crank right beside the door. Pry it to close the gas valve, then head inside the hole in the wall and towards the next room.
Inside the next room you'll start hearing some men talking. Hide behind the corner of the door and peak at them. Then ready your bow and shoot the barrel that's beside them. This will cause it to explode, instanlty killing the two bandits beside it.
A third one will then appear from the stairs. Shoot him too then climb up the stairs beside where the barrel was.
Ready your bow when you get to the second floor. A bandit will drop down from the vent and attack you. Kill him then enter through the vent that he exited from.
Inside the next room there's a fallen generator near an open vent. Use the generator to reach the vent and get to the other side.
Inside the next room there's a gas valve on the right. Use your climbing axe to pry it open then use the other fallen generator to get back to the other room (the one you came in from).
Now grab one of the lanterns inside the room and press the right mouse button. Aim it towards the vent that you used to get in and out of the room and use the left mouse button to toss it over and cause an explosion.
After the room explodes head into the room where the bandit was trying to break in from. You'll see him crushed under some rocks. Approach him and you'll receive a submachine gun. The bandit will also ask you to kill him. Shoot him if you want to then head inside the room beside him.
Grab as much as you can inside the room then head for the door on the left side. You'll be ambushed and there's a lot of them.
You'll automatically go into survival instinct mode and time will slow down. Start killing as much of them as you can. I'm not sure if you can only kill 2 or I was too slow but eventually time will start to move normally.
After time goes back to normal head to the right side and climb up the higher platforms. You'll be able to pick them off faster from here while sustaining minimum damage.
Start killing them off one by one. Just make sure to stay behind cover as much as you can and only aim when you know you can kill them.
After you've killed a few of them a pyromaniac will come out. Focus your attention on him before taking care of the rest.
After you've killed all of them try to replenish your supplies by scavanging around the room. Then head towards the large door on the left side of the area.
Another bandit will come crashing down. Shoot his leg to incapacitate him, then finish him off with an up close finishing blow. After killing him head towards the door and pry it open.
Head inside the room and towards the control panel. Once you get near it a cutscene will play.
After the cutscene salvage as much as you can from the room then head out through the hole with arrows pointing towards it.
Inside you're going to have to make your way through hot pipes. Although you only need to press up and Lara will dodge everything automatically. At the end you'll need to kick the vent open with F.