EE was unrolling end of a roll of 48"" conveyor belt. End was nailed to main roll. Main roll of belt was setting on forks of forklift but not secured. He was standing between belt roll & a mantrip. When he pulled on the nails, belt rolled off the forks & pushed him into mantrip pinning his rt leg between belt & side of trip. As he fell into seat of trip, his leg remained pinned