EMPLOYEE STATED THAT DURING THE MINING OF THE #86 CHAIN PILLAR THAT A PRESSURE BUMP OCCURRED. WHEN THE BUMP HAPPENED THIS CAUSED A PORTION OF THE COAL RIB TO FALL OUT AND STRIKE THE EMPLOYEE. THE COAL RIB WAS FIVE FOOT IN LENGTH BY TWO FOOT IN WIDTH BY TWELVE INCHES IN DEPTH. THE HEIGHT OF THE ENTIRE COAL RIB IN THE WORKING AREA WAS NINETY INCHES.