A FALL WAS DISCOVRED IN THE NO. 5 ENTRY OF PANEL 4 RIGHT OFF 2-LEFT OFF 2 RIGHT MAIRS. THE FALL WAS APPROX 500' OUTBY THE ACTIVE SECTION AND MEASURED APPROX 20'LX20'WX10'H. THE FALL WAS SURV EY STAITON 2159. THERE WERE NO INJURIES OR EUQIPMENT INVOLVED. VENTILATION WAS NOT AFFECTED.