Replacing pipe unions & nipples on a HAV unit, taking out the gas unit and tightening an elbow using a 3"" x 3' cheater pipe over a 36"" aluminum pipe wrench. The cheater pipe slipped off the pipe wrench, bounced off the bridge of his nose and then sliced into the left nasal alae area. He had a 3.5 cm curvilinear laceration that was tangential and down to the deep cartilage.