THERE WAS AN UNGUARDED OPENING NEAR WHERE THE BASE OF A LADDER WAS SET UP. THE INJURED EMPLOYEE CLIMBED THE LADDER BEFORE HIS CO-WORKER CAME BACK TO THE WORK LOCATION FROM LUNCH. THEY HAD BEEN HOLDING THE LADDER FOR EACH OTHER. AS HE CLIMBED THE LADDER, THE BOTTOM SLIPPED & FELL THROUGH THE HOLE & HE FELL THROUGH THE HOLE TO A PLATFORM 12' BELOW.