What safety device is identified as the anti-two-block (A2B) device?

• A. Anti-two-block device
• B. Boom stops
• C. Crane level indicator
• D. Rail clamps

Answer: (A)

Two-blocking happens when the hoist block gets so close to the upper block or the boom tip that the line or blocks contact each other, which can lead to rope damage, equipment failure, or a dangerous sudden load movement. The anti-two-block device is specifically designed to prevent that scenario by monitoring how close the hoist block is to the upper block or boom and automatically stopping or limiting hoist movement before contact occurs. In operation, when the system detects that the hook block is approaching the point where two-blocking could happen, it interrupts the hoist control to stop raise or limit travel, safeguarding the crane and crew. This safety device is different from boom stops (which prevent excessive boom extension), a crane level indicator (which shows tilt), or rail clamps (which secure the crane to rails); none of those directly prevent two-blocking.