This is the second part of the Death Factory Mission in Hitman: Absolution. In it you make your way through the decontamination area of the facility, disable the security and make your way to the silo entrance. This guide explains how to get through this part of the mission on the hardest, purist, difficulty. It does not explain how to complete the different challenges in this area.
At the end of this guide is a YouTube video with a visual version of this guide.
Disable Security System
At the start make your way down the corridor. Pick up one of the bottles off the table ahead. Make sure you stay as close as possible to the left wall when you walk past the door the guard entered:
Locate the Silo Entrance
Then go into the bathroom. On the left wall is an air ventilation shaft: