Complex sentence: Not heeding Duncan's directions, one last group takes an elevator to the ground, which proves fatal as the group is killed when the elevator stops on the fire's floor and opens its doors, exposing the occupants to the deadly flames.
Split into simpler sentences: Not heeding Duncan's directions, one last group takes an elevator to the ground. This proves fatal as the group is killed when the elevator stops on the fire's floor and opens its doors, exposing the occupants to the deadly flames.