First, grab the zip-line and wait until Lara lands in a new spot. Head south.
Go inside the warehouse on the right and check it out. There is a Fire Striker on one of the tables. Once you pick it up you can stop worrying about sources of fire to light the torch with; you'll be able to do it just by holding the action button.
Light the torch and go back to the tanks you've passed by earlier. Locate and turn the interactive valve. Stand next to the puddle of gasoline and use the torch. The only thing left to do is to retreat and wait for a pretty explosion, after which the game will trigger and interesting cut-scene (reward: 400 XP).
As soon as you regain control over Lara, wiggle the analog stick left and right (or use directional keys) in order to avoid the bigger obstacles while sliding down. Press the action button when you reach the edge (screenshot).
It's not over yet; to avoid death under crushing circumstances you'll need to leap across to the nearby ledge (reward: 500 XP).