While checking beltline with co-worker, co-worker went up to top of hopper to unlodge a rock that was wedged. Hard hat fell off of co-worker onto beltline below. Emp attempted to grab hard hat and ran, slipping, and falling on his Lt. side. Strain to Lt. Shoulder, continued complaints of discomfort, examination showed tear / Lost time on 01/29/14 when surgery was performed.