On the morning of 5/29/2015, employee arrived at work at 6:00 am. At about 6:05 he was securing a line to roll a cover on a barge. The hook somehow dislodged and became airborne striking the employee in his left upper arm. The hook was 4" and weighed approximately 3 pounds. The cover of the barge became wedged and put tension on the line and then the hook became dislodged striking the employee.