Which statement best describes anti-two-block and how it is achieved?

• A. It is unrelated to block contact.
• B. A device or system that prevents the hook block from contacting the boom tip; achieved via limit switches, sensors, or mechanical limits.
• C. It uses wind speed to adjust hoist speed.
• D. It relies on operator's manual communication only.

Answer: (B)

Anti-two-block is a safety feature that prevents the hook block from coming into contact with the boom tip. It achieves this by using devices that sense the relative position of the hook block and the boom—such as limit switches, proximity sensors, or mechanical stops—and automatically stop or limit hoist movement before contact can occur. In practice, when the hook block approaches the safe distance from the tip, the control system interrupts hoisting or reduces speed to keep the block clear of the boom end. This protection is built into the crane’s safety interlocks and control logic, so it works automatically rather than relying on the operator's manual commands.

This concept isn’t about wind speed or manual communication. Wind or weather controls might affect crane operations in other ways, and manual signaling is not sufficient to prevent a two-block condition on its own, since the danger can happen quickly and from a distance.