How does an anti-two-block device function and what are common types?

• A. It detects proximity between the hook block and boom tip to prevent a full hoist; common types include mechanical, electronic (sensor-based), or hydraulic interlocks
• B. It measures wind speed to adjust hoist
• C. It records operator hours for maintenance
• D. It automatically adjusts the load chart for weather

Answer: (B)

An anti-two-block device is a safety feature that prevents the hook block from getting too close to the boom tip, which could cause two‑blocking and lead to rope damage, crane damage, or serious injury. It works by detecting when the hook block approaches a defined proximity to the boom tip and then automatically stops or limits hoisting to prevent contact. Detection can be done in several ways: mechanical interlocks use a physical rod or linkage on the hook block to trigger a limit switch; electronic or sensor-based interlocks rely on proximity sensors or switches to sense distance and cut hoist power; and hydraulic interlocks use hydraulic circuits to restrict movement when proximity is reached. These approaches share the goal of keeping the hook block and boom apart during lifting. This device doesn’t measure wind speed, adjust the load chart for weather, or log operator hours; its purpose is specifically to prevent two-blocking.