Mobile Crane Operator Test 1 Flashcards

A mobile crane is operating on a 3% side slope with a 100-ton capacity chart. The operator must apply a side slope derating factor. If the manufacturer's load chart derating table specifies a 15% capacity reduction for a 3% side slope, what is the maximum allowable load the crane may lift?

Answer: 85 tons

A 15% derating on a 100-ton chart means the crane's capacity is reduced by 15 tons (100 × 0.15 = 15), leaving a maximum allowable load of 85 tons. Operating on a side slope shifts the crane's center of gravity laterally, reducing tipping stability, which is why manufacturers require this derating.

During a pick-and-carry operation with a rough-terrain crane, the load begins to pendulum swing perpendicular to the travel direction. Which action BEST addresses this hazard while maintaining load control?

Answer: Stop travel immediately and use the load line to dampen swing before proceeding

Stopping travel immediately removes the driving force causing the pendulum swing. The operator then uses controlled boom or load-line movement to dampen the oscillation before resuming travel. Accelerating or rotating the superstructure during an active swing can amplify the pendulum effect and risk tipping.

A crane's load chart shows a 20-ton capacity at 60-foot radius over the rear. The rigging consists of two 3/4-inch wire rope slings in a basket hitch at a 45-degree vertical angle. Using the tension factor for 45-degree slings (approximately 1.41), and each sling has a rated capacity of 8.4 tons in a straight pull, what is the governing limitation for this lift?

Answer: The sling capacity — each sling will be overloaded at loads above approximately 11.9 tons total

In a basket hitch at 45 degrees, each sling leg carries tension = (load/2) × 1.41. For the slings not to be overloaded, load/2 × 1.41 ≤ 8.4 tons → load ≤ 8.4 × 2 / 1.41 ≈ 11.9 tons. Although the crane chart allows 20 tons, the rigging becomes the governing limitation at approximately 11.9 tons — well below the chart capacity.

An operator is using a telescoping boom all-terrain crane. The load chart specifies capacities for 'on outriggers, fully extended.' The right-rear outrigger pad is resting on a concrete pad that is visibly cracked, and the site engineer has not yet assessed it. The signal person says the job is behind schedule and instructs the operator to proceed. What is the correct action?

Answer: Refuse the lift and notify the lift director; do not operate until ground conditions are confirmed adequate

ASME B30.5 and OSHA 1926.1416 require the operator to refuse operation when ground conditions are questionable and a competent person has not confirmed their adequacy. Proceeding under a schedule directive — or improvising by operating on fewer outriggers — violates safety regulations and voids the load chart, which is based on fully extended, properly supported outriggers.

According to ASME B30.5, what is the MINIMUM required clearance between any part of a mobile crane and an energized overhead power line operating at 345 kV?

Answer: 20 feet

ASME B30.5 and OSHA 1926.1408 require minimum clearances that increase with voltage. For lines above 350 kV, 25 feet is required; for lines from 50 kV to 350 kV, the minimum is 10 feet plus 0.4 inches per kV over 50 kV. For 345 kV: 10 ft + (295 kV × 0.4 in/kV) = 10 ft + 118 in ≈ 10 ft + 9.8 ft ≈ 19.8 ft, which rounds to the 20-foot minimum specified in table for this voltage range.

A crawler crane with a luffing jib is rigged and the operator notices the jib backstay pendants are slack while the jib is positioned at 75 degrees from horizontal. Which condition does this MOST likely indicate?

Answer: The jib is over-vertical or the luffing rope has too much tension, creating a condition where the jib could jackknife

Slack backstay pendants on a luffing jib at high angles indicate that the jib may be near or past vertical, or that the luffing line tension is pushing the jib toward a jackknife condition. This is a critical safety hazard — if the jib goes over vertical, it can collapse backward onto the main boom. The crane must be stopped immediately and the jib carefully lowered to a safe angle. Backstays should always be in tension when the jib is in its operating range.