A 57-year-old male electrical mechanic (the victim) died after falling through an unguarded floor opening. The victim was measuring, cutting, and color coding electrical cable with two coworkers on the unfinished fourth floor of the building at the time of the incident. The floor measured 108 feet wide by 300 feet long and contained 1 unguarded opening which measured 54 inches wide by 43 inches long. Just prior to the incident, the victim and a coworker were rewinding electrical cable. One coworker was positioned at the spool manually turning it; the victim was holding onto the end of the cable, walking backwards and pulling the cable straight so it would rewind evenly. The coworker felt the spool jerk out of his hands and saw the spool fall through the floor opening. Neither coworker saw the victim step backwards into the unguarded floor opening. The victim fell 45 feet to the concrete floor blow, and the spool fell on top of him. Workers on the first floor heard the victim fall and ran to give assistance. One of the coworkers ran to the general contractor's trailer where a call was made for emergency services. Fire department first responders arrived within 2 minutes after receiving the call and checked the victim. Due to the extent of injuries, no first aid was administered. The victim was pronounced dead by a medic at the scene. NIOSH investigators concluded that, in order to prevent similar occurrences, employers should: Ensure that employees on walking/working surfaces are protected from falling through holes more than 6 feet above lower levels by personal fall arrest systems, covers, or guardrail systems erected around such holes. Ensure that employers on multi-employer work sites utilize contract language that clearly defines the safety responsibilities of each contractor prior to the initiation of work. Remove employees from areas where an imminent danger has been identified and corrective action has not been completed.