Anti-two block devices are operational safety devices that can fail and must not be relied upon to stop movement of the hoist.

• A. True
• B. False
• C. They always stop movement
• D. They are optional

Answer: (A)

Anti-two-block devices are safety interlocks that detect when the crane’s blocks are in a position where a two-block condition could occur and they will interrupt hoist movement to prevent damage or crushing. But they’re not guaranteed to stop movement in every situation because there are possible failure modes: sensor or wiring faults, power loss, controller or relay failures, misalignment, or wear can prevent a trip from occurring. Because of these potential failures, you should not rely on them as the sole means of stopping the hoist. They belong to a layered safety system, complemented by regular maintenance and testing, proper operating procedures, independent limit switches, mechanical stops, and trained operator practices. So the statement is true: they are essential safety devices that can fail and must not be depended on to stop movement every time.