NCCCO - National Commission for the Certification of Crane Operators Anti-Two-Block Devices and Safety Systems 1

Question 1

When an anti-two-block (ATB) device activates during a crane operation, which crane functions are typically disabled to relieve the condition?

Accepted Answer

Hoist-up, boom-up, and boom-extend are disabled, while hoist-down and boom-down remain available

Answer

ATB systems are designed to cut out the movements that worsen a two-block condition (hoisting up, booming up, telescoping out) while allowing the reverse movements that relieve it, so the operator can safely lower the block away from the boom tip.

Question 2

According to standard crane safety practices and OSHA 29 CFR 1926.1416, how frequently must an anti-two-block device be functionally tested?

Accepted Answer

At the beginning of each shift before any crane operations begin

Answer

OSHA requires that safety devices, including ATB devices, be tested at the start of each shift to confirm they are functioning properly before the crane is put into service.

Question 3

Which component is the primary sensing element in the most common type of mechanical anti-two-block system found on boom cranes?

Accepted Answer

A weighted bob or warning weight suspended from the boom tip by a chain or cable, connected to an electrical cut-out switch

Answer

The weighted bob hanging from the boom tip by a chain is the standard mechanical ATB sensing element. When the rising hook block contacts and lifts the weight, it actuates the cut-out switch, disabling dangerous crane movements.

Question 4

An operator notices the ATB alarm is sounding and crane functions are disabled, yet the hook block appears to be well below the boom tip with plenty of clearance. What is the most likely cause?

Accepted Answer

The warning weight or its suspension chain has become snagged on rigging, the load, or a structure, prematurely lifting the switch

Answer

A premature ATB activation with visible clearance almost always means the warning weight has been caught or tangled by something other than the hook block itself, physically triggering the switch. The weight must be freed and the device reinspected before resuming operations.

Question 5

A crane is rigged with both a main hoist line and an auxiliary hoist line. Under OSCE and OSHA 29 CFR 1926.1415 requirements, what is the correct ATB configuration?

Accepted Answer

Each hoist line that is capable of experiencing a two-block condition must be equipped with its own dedicated ATB device

Answer

Regulations require that every hoist line capable of two-blocking be independently protected. A single device cannot monitor two separate lines, so both the main and auxiliary hoists must each have their own ATB system.

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

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

NCCCO - National Commission for the Certification of Crane Operators Anti-Two-Block Devices and Safety Systems 1