Abstract: At approximately 8:25 a.m. on August 31, 2011, a crew of four were working for Nibbi Bros. Associates, Inc. dba Nibbi Concrete on a multi-story project located in San Francisco, CA. Employee # 1, Employee # 2 and Employee # 3 were carpenters and the fourth was the crew carpenter foreman. The crews pour approximately 330 cubic yards of concrete on the roof deck and near completion when an area of roof deck dropped about 4-inches over a stairwell. The crew attempted to lift the section of sinking roof deck by stabilizing the forms from further movement. The foreman required the crew to work under the load in attempt to lift the loaded roof deck false work forms. The crew placed a hydraulic jack over a beam that was supporting their platform, and placed a shore post between the jack and the sinking false work beam above. As the crew applied pressure to the jack, the center platform supporting beam overloaded and broke in half. Employee # 1, Employee # 2 and Employee # 3 fell 15, 20 and 30 feet to the steel stairs below. They were buried by false work, shoring and about 5 yards of wet concrete resulting in serious injuries. The foreman managed to grab a guardrail and only suffered minor injuries. The San Francisco Fire Department reported the accident to the San Francisco District Office of DOSH. The Division's investigation determined that the false work erected in stairwell number four (4) for the roof deck, was not engineered correctly and subjected to load exceeding its capacity. In an attempt to stabilize and lift the overloaded false work, the employer overloaded their working platform center support beam that broke in two, causing a catastrophic failure of the platform and the false work above.