That's where the roof is intentionally collapsed to retrieve more coal. Retreat mining has been going on for generations and is considered standard practice in mines where coal reserves are running out. It involves yanking supporting pillars of coal from inside the mine and letting the roof collapse as miners and equipment work their way out.
The men were killed Monday night at the Brody Mine No. 1. Federal regulators say the mine had so many safety problems officials had deemed it a "pattern violator," a rare designation reserved for the industry's worst offenders.