While preparing the rig floor for RIH SR String, the Roustabout was installing the hand rail. The Driller noticed, that the rig floor slips (part of the Safety Floor) cover was not set. He instructed the Roustabout to install the Safety Floor Cover. The Safety Floor Cover was hanging on the winch line beside the v-door. The Driller started to raise the Safety Floor Cover by operating the winch line. The Safety Floor Cover got stuck on the rig floor. The Roustabout stepped in and tried to release it by pushing the winch line. As it was under tension it released and hit the Roustabout near his lips.