After leaving the elevator, head to the left and you'll find another collapsed part of the street. Use the slope to get down on the platform below.
Directly in front of the slope is a metal pipe. Jump on it and use it to climb back up on street level.
Once again ride down the slope and don't forget to slow yourself down by pressing the RMB to avoid taking damage when you fall to the ground too quickly.
Your first real look at the dust. Slide down further until you get to the street below. Now while in the dust your stamina will continue to deplete. You can either drink something to replenish it or get back on higher grounds. Of course no one wants to waste resources so we'll take the other option.
After getting down on the street, head right. Approach one of the metal beams that support the train and you'll find that there's a climable part of it.
Climb out of the fog and use the small metal ledge that's still connecting the two parts of the rails to make it to the other side.
Move across the rails and climb down on the left side of the tracks. This is important, you must climb down on the left side.
When you're back in the dust again, turn around and head for the street on the right side. The game will show you where to go, so cross the street and climb up on the beams to get inside the building.