Hostages Secured Achievement
Saved the hostages in the Transit Yards
At the very end of Mission 7, Transit Yards, you will be pursuing the lead Engineer aboard a train. Make sure you don't shoot any civilians or use any explosive gadgets when taking out the enemies inside the carts. When you reach the end of the train, there will be two civilian hostages. Do not move forward! Quickly throw some sleeping gas in between both hostiles to knock them out. The achievement will unlock after the cutscene begins.