An employee was applying trowel finish to double tees. As the employee started the trowel, he discovered it was set to full throttle. He struggled to get the trowel machine under control. The trowel blade contacted a portion of the double tee side rail. The blade stopped, but the trowel continued to rotate, throwing the employee off of the form and onto the ground on his right side. The employee was then struck by the trowel machine control bar.