EE was operating left side of the roof bolter on the 12 Right Section in the # 1 entry approx. 50 ft. inby survey station 25484 & as he walked towards the end of the roof bolter a rib measuring about 76"" high x 84"" wide by 26"" thick rolled off behind the line curtain striking the employee against the bolter resulting in fractures to left shouder, ribs, sternum & back.