High Risk Work Licence - Slewing Mobile Crane C1 (100t) common mistakes
High Risk Work Licence - Slewing Mobile Crane C1 (100t) · Understand the traps and how to avoid them.
Calculating the lift radius from the crane's slew centre to the load's near edge, or from the front bumper, instead of measuring horizontally from the centre of rotation to the centre of gravity of the load (including hook block and rigging), then reading the load chart at that larger radius.
Candidates picture the radius as the distance they can see on the ground and forget that the chart radius is defined from the slewing axis, and that the load's centre of gravity - not its nearest point - governs. Charts are unforgiving at long radius, so a 0.5 m underestimate can drop capacity by several tonnes and the candidate never notices the discrepancy.
What to do instead
Before every lift, mark the slew centre on the ground, drop a plumb line from the load's CoG, and measure that horizontal distance with a tape. Add the hook block, slings and any attached spreader to the load mass. Practise reading a chart at three radii with the same boom length and compare the capacity drop so the sensitivity becomes intuitive.
Treating the load chart as valid for any configuration, ignoring the specific conditions printed on the chart: boom length, jib stowed or erected, outrigger beam fully extended or intermediate, counterweight fitted, and the duty/rating the chart is issued for.
Charts come as families of tables and candidates grab the first table that looks right, or memorise one capacity figure from a familiar crane. They also assume 'fully extended outriggers' applies when the beams are only partly out, which changes the rating dramatically.
What to do instead
Work through a fixed checklist before reading any chart: confirm boom length, jib configuration, counterweight, outrigger beam positions and pad condition, then select the matching table and note the notes and warnings on that page. Verbally state the chart conditions to the assessor as part of the lift plan.
Rigging loads without confirming the sling angle factor, using a single vertical-capacity figure for a multi-leg sling, or assuming the load is shared equally between legs when the CoG is off-centre.
Candidates multiply the SWL by the number of legs, or use 45-degree factors for legs actually at 30 degrees from horizontal. Unequal leg loading from an offset CoG is invisible until a leg overloads, and shackle or hook orientation errors compound it.
What to do instead
Calculate each leg's tension from the actual included angle and the CoG position; use the sine of the angle to the horizontal for vertical share. Mark the CoG on the load, use a spreader beam where angles are steep, and check that shackle pins and hooks are loaded in their rated direction. Rehearse one worked example with an offset CoG until the arithmetic is automatic.
Setting up with outrigger pads on uncompacted fill, near a trench edge, over a service pit or on a slope, without assessing ground bearing pressure or the effect of the outrigger load spreading through the pad.
The crane looks level and the pads look big, so candidates skip the ground assessment. They also fail to account for recent rain, backfilled excavations, underground drains and the fact that outrigger loads can be far higher than the lifted load because of the crane's own mass and leverage.
What to do instead
Obtain or estimate ground bearing capacity, calculate pad pressure (outrigger load divided by pad area), and keep pads back from excavations by at least the depth of the excavation or a geotechnical allowance. Use certified pads or mats, check level in both axes, and re-check after the first load is applied and the crane has settled.
Relying on a spotter's voice or a two-way radio alone, or accepting an unqualified person's signal, instead of confirming a single designated dogger, agreed hand and whistle signals, and a stop signal that anyone may give.
Site noise, multiple people giving directions and unfamiliarity with the standard signal set cause confusion. Candidates also forget that the operator must obey a stop signal from anyone, and that radio failure needs a pre-agreed fallback.
What to do instead
At the pre-lift briefing, nominate one signalling dogger, confirm line of sight, test the radio, and agree the full signal set including emergency stop and the all-clear. State aloud that any person may give a stop signal and it will be obeyed. If communication is lost, stop the movement and hold until it is restored.
Planning a multi-crane lift by simply adding the two crane capacities and splitting the load 50/50, without a written plan, load-share calculation, or allowance for the load transfer as each crane takes up.
Candidates think two cranes equal twice the capacity. In reality the load share depends on hook heights, radii and geometry, and can shift dramatically as the load is raised or travelled, overloading one crane. The absence of a documented plan is also a compliance failure.
What to do instead
Treat multi-crane lifts as high-risk: prepare a documented lift plan with the load-share calculation at each stage, keep each crane within a reduced percentage of its chart, maintain the planned geometry, and use a single supervisor directing both operators. Verify with a trial lift of a few centimetres and check for load shift before committing.
Working near overhead powerlines without establishing the exclusion zone from the correct voltage-based distance, or assuming that because the crane is not touching the line it is safe, including for the dogger holding the load or tag line.
Candidates estimate distance by eye, confuse phase-to-phase and phase-to-earth voltages, or forget that electricity can arc across an air gap and that the whole crane and load become live. Tag line handlers and people steadying the load are often overlooked.
What to do instead
Identify the line voltage from the owner or signage, apply the regulated exclusion distance for that voltage in all directions including boom and load travel, and use a spotter if working near the boundary. Where de-energising or isolation is not possible, use a documented control such as a limiting device. Brief everyone that tag lines near lines are prohibited and that a crane contacting a line must be evacuated, not touched.
Performing a pre-operational inspection as a box-ticking ritual - walking around without checking wire rope for broken wires, bird-caging, kinks or corrosion, without testing limit switches, the load moment indicator, the anti-two-block, the horn and the brakes, and without recording defects.
Familiarity breeds skipping. Candidates glance at the rope, assume the LMI is calibrated, and do not know how to function-test the two-block or the rated capacity limiter. Defects found are not written down or reported, so they recur.
What to do instead
Use a structured inspection sheet covering rope, sheaves, hooks and latches, brakes, limit switches, LMI/RCI, anti-two-block, outriggers, tyres, fluids and fire extinguisher. Function-test each safety device as part of the check, record results, and tag out and report any defect rather than 'working around' it. Practise the inspection sequence until it takes a consistent, repeatable path.
Lifting a load without establishing its mass and CoG - guessing from appearance, using a nominal weight, or ignoring attached items, water, debris or contents - and then rigging from an assumed balance point.
Candidates trust the load's marked weight, which may be wrong or refer to a different item, or they estimate by eye. Attachments, pallets, residual material and asymmetric shapes shift both mass and CoG, and the resulting tilt or swing surprises the operator.
What to do instead
Verify mass from drawings, weighbridge, shipping documents or by calculation, and add rigging and attachments. Determine CoG by symmetry, calculation or a trial lift just clear of the ground, then rig so the hook is over the CoG. If the load tilts on trial lift, lower it and re-rig rather than chasing it with the crane.
Handling an emergency by improvisation: not knowing the procedure for powerline contact, fire, load runaway or a person injured under a load, and not knowing the location of the isolator, extinguisher or first-aid equipment.
Emergency procedures are read once during induction and never rehearsed, so under stress the candidate freezes or does the wrong thing - for example touching a crane in contact with a live line, or jumping from the cab instead of staying put. First-aid knowledge is assumed rather than checked.
What to do instead
Before work starts, locate the isolation point, extinguisher, first-aid kit and emergency contacts, and brief the crew on the response to powerline contact, fire and injury. Rehearse the powerline scenario: stay in the cab, warn others away, call for the line to be de-energised, and only leave if fire forces it, jumping clear and shuffling away. Confirm current first-aid qualifications and the site's rescue plan for a suspended-load casualty.