EE was emptying two 32-gal. plastic trash cans with wheeled dolly for transporting from the Lab. He brought the cans to the Burner Floor dumpster to empty. While lifting one, dolly detached and fell to the floor. He had to lift it (about 20 lbs.) to a height of 50"" to dump the can over the lip of the dumpster. He felt a ""twinge"", soreness in right shoulder.