EE WAS CLIMBING AN UNSECURED LADDER THE INITIAL START-UP OF THE WORK SHIFT. EE AND OTHER COWORKERS WERE IN PROCESS OF GETTING OUT OF THEIR EQUIPMENT & SETTING UP IN ORDER TO WELD HOOKS ON THE CAB PROTECTOR TO SECURE THE LADDER. INJ EE CLIMBED THE LADDER TO GAIN ACCESS TO THE TOP OF THE CAB PROTECTOR & THE UNSECURED LADDER SLID OUT FROM UNDER HIM CAUSING HIM TO FALL.