What action does a signal person intend the operator to perform if he extends his arm at shoulder height, makes a fist with his hand, and sticks his thumb up?

A signal person extending their arm at shoulder height, making a fist, and sticking their thumb up is indicating the operator to raise the boom. This hand signal is widely recognized in construction and hoisting operations as a clear and specific way to communicate the action of lifting the boom or the load being lifted.

Using a fist with the thumb pointing upwards creates an unambiguous visual for the operator to understand that elevation of the boom is required. In environments where clear communication is paramount for safety, such visual signals are critical to ensure all crew members are aware of the intended actions.

Additionally, the other options do not correlate with this particular signal. For instance, lowering the boom would typically involve the arm being extended downward or pointing downward to indicate that direction. Moving forward would usually require a different set of signals, often involving more dynamic movements of the arms. Stopping operations generally involves raising both arms to signal for an immediate halt, contrasting with the movement indicated by the fist and thumb up.