Communication and Standard Hand Signals
One signalperson, one voice
Designate a single qualified signalperson who is in the operator's view and whose signals the operator understands. Anyone may give a stop signal and the operator must obey it immediately; only the designated signalperson may direct movement. When the load or signalperson will be out of sight, use radio or telephone communication with an agreed verbal protocol and test it before the lift.
The standard signals
Learn the ASME B30.2 and OSHA set as a vocabulary. Raise and lower are shown with the forearm and index finger pointing up or down while the hand circles. Stop is one arm extended, palm down, held still. Emergency stop is both arms extended, palms down, moved back and forth. Bridge travel is shown by extending the arm and pushing in the direction of travel; trolley travel by pointing with the finger in the direction the trolley should move. Dog everything, meaning suspend operations, is hands clasped in front of the body. Use main hoist and use auxiliary hoist are signaled by tapping the head and the elbow respectively.
Traps
Questions test whether you obey an unauthorized stop signal (you do), whether a signal should be acknowledged (make eye contact and repeat the signal before moving), and whether a radio dead spot can be covered by a camera or a bystander (it cannot - stop until communication is restored). Signals that are ambiguous or argued about mid-lift are the ones that cause injuries.
Rule of thumb: when in doubt, stop and re-establish communication - a stalled lift costs minutes; a misunderstood signal costs fingers.