NCCCO Anti-Two-Block Devices and Safety Systems 5 — Questions and Answers
Question 1: Which of the following is a recognized method for manually testing an A2B device without risking actual two-blocking?
- Raise the hook rapidly to its physical stop
- Manually lift the bob-weight or actuating device by hand to simulate contact (Correct answer)
- Lower the boom until it contacts the hook block
- Disconnect the hoist rope and run the drum at full speed
Correct answer: Manually lift the bob-weight or actuating device by hand to simulate contact
Manually lifting the bob-weight simulates the hook block making contact with the boom tip and verifies the switch cuts out the controlled functions safely.
Question 2: A crane operator notices the A2B indicator light is on but the crane is not near two-block condition. The MOST likely cause is:
- The load is too heavy for the boom angle
- A damaged or shorted wire in the A2B circuit (Correct answer)
- The counterweight is improperly positioned
- The outriggers are not fully extended
Correct answer: A damaged or shorted wire in the A2B circuit
A constant A2B warning when the hook is well below the boom tip usually indicates a wiring fault, damaged switch, or short circuit in the A2B system.
Question 3: What is the primary reason crane manufacturers require A2B devices to cut out BOOM UP as well as HOIST UP?
- Raising the boom increases swing radius and reduces stability
- Raising the boom reduces the vertical distance between the hook block and boom tip (Correct answer)
- Boom up motion increases wire rope tension independently
- Raising the boom changes the load chart ratings
Correct answer: Raising the boom reduces the vertical distance between the hook block and boom tip
As the boom angle increases, the geometry of the crane shortens the effective distance between the hook block and the boom tip, potentially causing two-blocking.
Question 4: During a pre-shift inspection, the operator finds the A2B bob-weight is missing from the load block. The correct action is:
- Proceed with the lift and replace the weight at the end of the shift
- Operate at reduced capacity until the weight is replaced
- Remove the crane from service until the A2B device is restored (Correct answer)
- Use a spotter as an alternative to the missing A2B component
Correct answer: Remove the crane from service until the A2B device is restored
A missing or non-functional A2B component renders the safety system inoperable; the crane must be taken out of service until the device is repaired.
Question 5: In a luffing jib crane configuration, two-blocking risk is GREATEST when:
- The luffing jib is at its lowest angle and the hook is being raised (Correct answer)
- The main boom is at maximum radius
- The crane is slewing at maximum speed
- The counterweight is at its maximum extended position
Correct answer: The luffing jib is at its lowest angle and the hook is being raised
At low luffing jib angles, the tip sheave is close to the hook block's maximum reach, making two-blocking easier to trigger when hoisting.
Question 6: Which documentation must accompany an A2B device repair to ensure compliance?
- A written note from the operator describing the malfunction
- Maintenance records per the manufacturer's instructions and applicable standards (Correct answer)
- Only a verbal confirmation from the maintenance technician
- An annual OSHA inspection report
Correct answer: Maintenance records per the manufacturer's instructions and applicable standards
All repairs to safety devices must be documented in maintenance records in accordance with manufacturer specifications and ASME/OSHA requirements.
Question 7: If a crane's A2B device activates while a load is suspended mid-air, which motion IS permitted after stopping hoist-up?
- Boom up to clear the load
- Hoist down to lower the hook block away from the boom tip (Correct answer)
- Telescope out to increase boom length
- Slew to reposition the load
Correct answer: Hoist down to lower the hook block away from the boom tip
Lowering the hook (hoist down) increases the clearance between the hook block and boom tip, safely resolving the two-block condition without load drop.
NCCCO Anti-Two-Block Devices and Safety Systems 5
Which of the following is a recognized method for manually testing an A2B device without risking actual two-blocking?