Mobile Crane Operator Test 1 Flashcards

A hydraulic mobile crane has an unladen weight of 180,000 lbs. The operator is lifting a 40,000 lb load with rigging weighing 2,000 lbs. The crane is set on four outrigger pads, each measuring 36 inches × 36 inches, with load assumed equally distributed. What is the approximate ground bearing pressure per pad?

Answer: 6,167 psf

Total system weight = 180,000 + 40,000 + 2,000 = 222,000 lbs. Divided equally among 4 pads = 55,500 lbs per pad. Each pad is 3 ft × 3 ft = 9 sq ft. 55,500 ÷ 9 = 6,167 psf. This calculation is critical before operating on any surface, as exceeding allowable ground bearing capacity can cause catastrophic outrigger failure.

Per ASME B30.5, when an anti-two-block (ATB) warning device activates during a lift, which response is correct?

Answer: All crane functions that could worsen two-blocking must cease; only motions that relieve the condition may be used

ASME B30.5 requires that when an ATB device activates, the operator must immediately stop all crane functions that could cause or worsen two-blocking. Only motions that relieve the condition — such as lowering the boom or lowering the hook — are permitted. Continuing to hoist, boom up, or telescope out risks snapping the load line, dropping the load, or structural boom damage.

A crane operator is preparing to lift a 72,000 lb load with 4,500 lbs of rigging using a crane whose load chart shows 85,000 lbs capacity at the planned configuration. Before the lift, the operator calculates the load as a percentage of rated capacity. Which regulatory consequence applies?

Answer: The lift qualifies as a critical lift under OSHA 1926 Subpart CC, requiring a written plan and designated person-in-charge

Total lifted weight = 72,000 + 4,500 = 76,500 lbs. As a percentage: 76,500 ÷ 85,000 = 90% of rated capacity. OSHA 1926.1408 defines a critical lift as any lift exceeding 75% of the crane's rated capacity. At 90%, a written critical lift plan and a designated person-in-charge are mandatory before the lift begins.

For load chart lookup purposes, how is the crane's working radius officially defined under ASME B30.5?

Answer: The horizontal distance from the axis of rotation to the center of the suspended load

ASME B30.5 defines working radius as the horizontal distance from the axis of rotation (the crane's center of rotation) to the center of the suspended load — not from the boom base, front of the carrier, or outrigger footprint. This distinction matters greatly at steep boom angles, where the horizontal distance is significantly less than the boom length, and operators must measure carefully to avoid using an incorrect (shorter) radius that would yield a higher, unsafe chart capacity.

During a pre-shift inspection of a lattice boom section, the operator notices a visible bow in one of the chord members — approximately 3/8 inch over an 8-foot span. Per ASME B30.5, what is the required course of action?

Answer: Remove the boom section from service immediately and have it evaluated by a qualified person before any further use

ASME B30.5 requires that any visible deformation of structural members — including bowing, bending, or cracking of chord members or lacings — results in immediate removal from service. There is no tolerance threshold that permits continued operation with a deformed chord; only a qualified person's evaluation can determine if the section may be repaired and returned to service. Derating or repositioning a deformed structural member are not recognized remedies.

A mobile crane's load chart specifies capacities for 'on outriggers — fully extended.' Due to site constraints, the operator can only extend the outriggers to approximately 75% of full extension. Which action correctly follows ASME B30.5 and OSHA requirements?

Answer: Consult the manufacturer's load chart data for intermediate outrigger extension positions, or contact the manufacturer directly if that data is unavailable

ASME B30.5 and OSHA 1926.1416 require that crane operations conform to the manufacturer's load charts. Many manufacturers publish separate capacity tables for intermediate outrigger extension positions (e.g., 50%, 75%). If such data exists in the load chart, the operator must use it. If it does not, the operator must contact the manufacturer for guidance before operating — self-calculated interpolation or arbitrary derating factors are not acceptable substitutes, as stability geometry is non-linear and varies by crane model.