An employee was prepping a room by installing fly lights and air filters. A guard/hand rail was not in place on the walkway leading to the rear catwalk at the time. While reaching over the unprotected area, the employee lost balance and fell from the second floor. He briefly caught himself on a 2 x 6 crosspiece before falling 6 feet through to the first floor. The employee sustained a subdural hematoma, rib fractures, and a laceration to the spleen.