NCCCO Anti-Two-Block Devices and Safety Systems 3

Question 1

When an anti-two-block (A2B) device activates during a lift, the crane operator should FIRST:

Accepted Answer

Stop all hook and boom motions that would worsen the condition

Answer

Upon A2B activation, the operator must immediately stop all crane motions that would further reduce the distance between the hook block and boom tip.

Question 2

Which type of A2B sensor is MOST commonly used on modern hydraulic cranes?

Accepted Answer

Weight-actuated switch with a hanging weight on the load block

Answer

Weight-actuated (pendulum or bob-weight) switches are the most common A2B devices, where the hanging weight lifts when the hook block contacts the boom tip.

Question 3

A2B devices are required to prevent unintended contact between the load block and the:

Accepted Answer

Boom tip or uppermost sheave

Answer

The A2B device prevents the load block or headache ball from contacting the boom tip or the uppermost load block sheave.

Question 4

When should a crane operator test the A2B device at the start of a shift?

Accepted Answer

Before beginning any lifting operations

Answer

OSHA and ASME B30.5 require operators to verify that all safety devices, including A2B devices, are functional before beginning lifting operations.

Question 5

If an A2B warning alarm sounds but the cut-out function does not engage, the operator should:

Accepted Answer

Immediately stop operations and tag the crane out of service

Answer

A non-functional cut-out means the primary two-blocking protection has failed; the crane must be taken out of service until repaired.

NCCCO (National Commission for the Certification of Crane Operators) Practice Test

NCCCO (National Commission for the Certification of Crane Operators) Practice Test

NCCCO Anti-Two-Block Devices and Safety Systems 3