The night guard is the run-ending threat in the prison. The chases at the end of Mineshaft and Rooftops are separate scenes with their own rules.
What gets you caught
He catches you in the halls at night. Close your own cell door before he reaches it. While that door is closed he does not enter the cell, and he does not see you digging. Leaving other doors, vents, or the carpet open is fine in the published tips.
He will enter a different prisoner's cell. Hiding there ends the run.
At night, the vent next to your cell reaches the sellers and the trade inmates. The vent inside the cell reaches the Janitor room and Security. Use those instead of the hallway.
Daytime
You can talk to inmates and the chef during the day. Be back behind your closed cell door before the guard arrives if you are still out when night starts. Lunch is the free food window. Spend your energy before you go, because the meal refills it.
Chase scenes
The Mineshaft chase starts when you drop into the tunnel. Move forward, avoid obstacles, follow sparkles at a split, and climb the ladder. One guide says there is no sprint in that scene.
The Rooftops chase starts as soon as the roof door opens. Jump the gaps and follow sparkles to the red helicopter.
The Janitor office is a stealth room, not that sprint. Crouch behind tables, collect 12 batteries, and fill the fusebox.
Revive
One encyclopedia entry says a guard kill can be revived only once. A player comment on a walkthrough says you cannot revive during the chase. No developer note confirms either rule, so do not plan on a second life inside a chase.
Videos also show an easy, medium, or hard selection. The written night-door rule above is the one the walkthroughs agree on. A difficulty screen that changes it was not documented.