A crane tip-over or boom collapse takes seconds and can kill instantly. Determining whether it was overload, rigging failure, ground failure, or a control error is forensic engineering under real stakes.
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A crane stays upright because its tipping moment — load times radius — stays inside the resisting moment built from its counterweight, outriggers, and the ground beneath them. Nearly every crane accident is, at bottom, a story about that balance failing: a load exceeded the chart for the configuration in use, a wire rope or sling parted below its rated strength, an outrigger pad sank into ground that was never load-tested, or the boom or load line contacted an energized line. The load chart, the rigging hardware, and increasingly the crane's own rated-capacity indicator each carry a record of which one it was — and reconstructing that record, before the site is cleared and the equipment repaired, is the difference between a defensible answer and a guess.
Crane and heavy-equipment failures cluster into a small number of mechanisms, and separating them is the first task of the investigation.
Lifting beyond the rated capacity for the boom length, angle, and radius in use — exceeding the tipping moment the counterweight and outriggers were sized to resist.
Soft, uneven, or unverified ground giving way under outrigger point loads that can exceed 100,000 lb per pad, tipping the crane without any overload at all.
Slings, shackles, hooks, and wire rope failing from wear, an improper sling angle, sharp-edge damage, or hardware rated below the actual tension in the line.
Boom, load line, or the load itself contacting or arcing to overhead energized conductors — a leading cause of crane-related electrocution.
The load block running up into the boom-tip sheave, or a wire rope, drum, or brake failing under load and releasing the load uncontrolled.
Boom section, pin, or turntable failure from fatigue cracking, an undersized weld, or a component operated beyond its inspection or service life.
Crane failures are reconstructed from the load chart the crane should have been operating under, the physical evidence at the scene, and — increasingly — the crane's own electronic load-moment data.
Crane and heavy-equipment accidents routinely put several of these in motion at once:
The crane's configuration, the failed rigging hardware, outrigger pad placement, and the LMI/RCI data are the evidence. Moving equipment or clearing the site before documentation can permanently erase the load-chart story.
By reconstructing the actual lift configuration — boom length, angle, radius, and outrigger extension — and comparing the resulting load moment to the manufacturer's rated capacity chart for that exact configuration. Mobile crane charts change with outrigger spread and tire pressure, not just boom length, so the comparison has to use the configuration as rigged, not as assumed. RCI/LMI data loggers, when present, often settle the question directly by recording the load and radius the system saw before the event.
Yes, and it happens more often than overload does. A crane's stability margin assumes level, firm ground and a load applied vertically and gradually. Side loading from a dragged or swinging load, a sudden stop, an out-of-level setup, wind loading on a large surface area, or ground that settles under one outrigger can tip a crane that was never above its chart. Distinguishing a load-chart violation from a site or dynamic-loading failure is usually the central question in these cases.
Two-blocking occurs when the load block or hook is raised too far and runs into the boom-tip sheave assembly with the hoist still powered. The continuing pull typically parts the wire rope, snaps a component, or damages the boom tip, and can drop the load or send debris outward without warning. Anti-two-block devices are standard on modern cranes, and whether one was fitted, functional, and not bypassed is a routine part of the investigation.
It depends on where the physical evidence points, which is exactly why the investigation matters. A load-chart violation implicates the operator and whoever approved the lift plan; a rigging failure implicates the rigger and the hardware's inspection history; a ground failure implicates whoever assessed the site and specified the outrigger mats; and a structural or mechanical defect implicates the equipment owner or manufacturer. OSHA 1926 Subpart CC's competent-person and qualified-person requirements for site assessment, rigging, and signaling create a paper trail that usually maps onto one of these.
The crane in its as-failed configuration and position, the rigging hardware exactly as it failed, the ground and outrigger mat condition, the load chart the crew believed applied, and the RCI/LMI data logger — its memory can be overwritten by subsequent operation. Photograph everything before the site is cleared, and do not repair, re-rig, or move the equipment until it has been documented.
Technical briefings from our work in this area.
A dropped load can come from a machine defect, from operation outside the chart envelope, or from rigging inadequate for the tension it saw. Each leaves different evidence under different standards.
readLoad moment data, rigging hardware, wire rope and the ground beneath the outrigger pads are all perishable. Recovery and site clearance destroy them in a predictable order, and quickly.
readA rated capacity chart is a set of conditions, not a number. Configuration, deductions, outrigger reactions and ground bearing capacity each decide whether the figure the crew read off the page applied.
readTell us what happened. We will triage it and connect you with the right expert — usually within one business day.