Abstract: At 8:00 a.m. on June 7, 2017, Employee #1 and Coworkers #1 and #2, employed by an industrial contractor, were working at a multi-employer construction site. They were clearing an area in preparation for setting up a mobile gantry crane. A stack of three sheets of oriented strand board (OSB) was in the way and needed to be moved. Coworker #1 and Coworker #2 each grabbed one sheet and pushed it up and out of the way against a wall. Employee #1 grabbed the third sheet, lifted it up on its side, and began walking forward towards the wall. He stepped into a previously unidentified floor hole and fell through onto an exhaust duct, a fall height of approximately 5 feet. Employee #1 struck an angle iron stiffener that was supporting the suspended ducting. Emergency services were called, and Employee #1 was transported to the hospital. He was admitted and treated for rib fractures and lacerations.