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

All crane functions are shut down simultaneously until the operator resets the system

Answer

Only the audible alarm is triggered; no functions are disabled automatically

Answer

The hoist is disabled, but all boom and swing functions remain fully operational

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

Once per month during a scheduled preventive maintenance inspection

Answer

Only after the device has been repaired, replaced, or the crane has been idle for more than 30 days

Answer

Annually, as part of the required third-party crane inspection

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

A hydraulic pressure transducer installed in the hoist line

Answer

A laser proximity sensor mounted on the underside of the hook block

Answer

A torque-limiting clutch integrated into the hoist drum mechanism

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

The load on the hook is exceeding the rated capacity, triggering the overload circuit

Answer

The load moment indicator is cross-wired with the ATB circuit and is generating a false signal

Answer

High wind is causing the boom to deflect downward, which electronically mimics a two-block event

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

A single ATB device on the main hoist line satisfies the requirement for both lines

Answer

An ATB device is only required on the auxiliary hoist because it is typically faster and harder to control

Answer

The crane manufacturer determines which lines require ATB devices; regulatory requirements defer entirely to the manufacturer's specification

Question 6

An operator simultaneously retracts (shortens) the boom and hoists upward during a pick. Why does this combination of movements dramatically increase the risk of a two-block condition?

Accepted Answer

Both movements simultaneously reduce the physical distance between the hook block and the boom tip sheave, compounding the closure rate

Answer

Boom retraction increases the load radius, causing the hook to swing outward and strike the boom chord

Answer

Retracting the boom causes hoist rope to go slack, leading to uncontrolled upward snap of the hook block

Answer

Hydraulic pressure shared between the two simultaneous functions reduces the ATB device's electrical supply, causing it to malfunction