Two employees were dismantling and removing a mast climber scaffold on the exterior of a building. They dismantled the unit to its lowest point (16 feet) and started taking the unit apart for final removal. The left side of the unit was removed (bridges), while the right side of the unit remained in place. When the last tie back was removed from the building, the scaffold unit slid back and collapsed. Both employees were tied off to the scaffold unit as it collapsed to the concrete ground which had other equipment pieces stacked around it. Both employees were hospitalized. Employee 1 sustained multiple fractures and a head laceration, and he required surgery. Employee 2 sustained a fractured right femur.