What is two-blocking and how can it be prevented?

• A. Two-blocking occurs when the rope becomes tangled around itself.
• B. Two-blocking is when the hoist reaches maximum load.
• C. Two-blocking occurs when the hook blocks contact the hoist sheave; prevent with proper travel limits, anti-two-block devices, and controlling rope height.
• D. Two-blocking happens when two cranes share the same hook.

Answer: (C)

Two-blocking happens when the hook block (lower block) comes up and contacts the hoist block (upper block), causing the load rope to be pinched between the sheaves. When the two blocks touch, the rope can be crushed, which may damage the rope, jam the hoist, or even cause a sudden load drop. Prevention focuses on keeping the blocks from meeting: use anti-two-block devices that stop the hoist if the blocks get too close, set and maintain proper travel limits so the hook can’t rise into the upper block, and control rope height during lifting to maintain adequate clearance. Regular maintenance and testing of limit switches and anti-two-block systems are essential to ensure these protections work. The other options describe different crane problems (rope tangled, maximum load, or two cranes sharing a hook) and do not describe two-blocking.