Employee was setting the bolter up for the first row in 7 Right. He was at the controls on the operator's side when the rib turned loose and the rock fell on its edge catching his right foot. The rock was 69"" long, 24"" wide at the widest point and 6"" at the narrow end. It was 11.5"" thick at the thickest point and 6"" at the thinest. This resulted in multiple fractures in his foot.