A crew was tasked with preparing a dummy blade ring to be rigged and lifted for use. The overhead crane was lowered over the dummy blade ring for connection. The injured employee then signaled to the crane operator to slowly take the slack out of the nylon sling. A shackle on one of the 5-ton chain fall's hooks caught on the underside of the dummy blade ring face. This caused the ring to tip and fall toward the injured employee and pin the employee between the dummy blade ring and a blade ring on the deck. The employee sustained contusions.