Abstract: On May 20, 2013, Employee #1, a roofer, and Coworker #1, both employed by a roofing contractor, were working at a residential building. They had removed the existing shake roof and were installing Oriented Strand Board (OSB) sheathing in preparation for installing a composition roof. The roof pitch measured 4/12. Employee #1 and Coworker #1 had removed approximately 10 OSB sheets from a stack of 38 sheets when, for reasons unknown, a brace identified as one of two OSB stickers holding the stack on the roof (one sticker on each end of the stack) broke. Ten sheets of sheathing slid off the roof. Employee #1, who was working below the stack, was struck by the falling sheets and thrown off the roof. He fell from an eave height of 9 feet. Emergency services were called, and the Sacramento Fire Department responded. Employee #1 was transported to University of California Davis Medical Center in Sacramento. He was treated for a compound fracture of his right wrist, a fractured hip, and a fractured pelvis. He required four days hospitalization. This fall was reported on May 20, 3013 by the Sacramento Fire Department to Cal/OSHA's Sacramento District Office. The employer did not report. The subsequent investigation determined that the OSB sheets had been stacked and secured on the roof by a third party delivery company. The roofing crew had inspected the stack of OSB sheets that morning and reported that it was secured.