High Risk Work Licence - Self-Erecting Tower Crane (CS) common mistakes
High Risk Work Licence - Self-Erecting Tower Crane (CS) · Understand the traps and how to avoid them.
Reading a load chart capacity at the boom tip radius or at the radius shown on the chart's top row, rather than at the actual working radius measured horizontally from the slewing centre to the load's centre of gravity, and then lifting a load that is heavier than the chart allows at that radius.
Candidates memorise a single 'safe working load' for the crane and treat capacity as a fixed number. Self-erecting tower cranes have short jibs and steep capacity fall-off with radius, so a small radius error near the jib tip produces a large capacity error. Candidates also forget that the radius grows as the jib deflects and the load swings outward.
What to do instead
Before every lift, measure the radius from the slewing centre to the load's centre of gravity at the position the load will occupy, add the jib deflection allowance, and read the capacity for that exact radius. Use the lowest capacity shown for a radius that falls between chart columns. Re-check the radius after the load is clear of the ground, because the jib unloads and the radius changes.
Treating the load weight as the sling's rated capacity or the hook's rated capacity, and ignoring the extra weight of the rigging, spreader beams, slings, shackles and any attached lifting accessories when comparing the total against the chart.
Candidates equate 'the load' with 'what the chart covers'. In practice the chart capacity covers the total suspended mass, and rigging can add a meaningful percentage on a small self-erecting crane with a low capacity. Candidates also misread sling markings as a working load limit in tonnes when the marking is a breaking strength or a colour code.
What to do instead
Calculate the total suspended mass as load plus rigging plus any attached accessories, and compare that figure with the chart capacity. Read sling and shackle markings as working load limit, not breaking strength, and confirm the marking is legible. If the total is within 90 per cent of capacity, treat the lift as a marginal lift and re-plan it.
Setting up the crane on ground that has not been assessed for bearing capacity, or on a base that is too small for the crane's outrigger or ballast footprint, and then jacking or erecting without checking for voids, services, slopes or soft spots under the base.
Candidates focus on the crane's own stability and forget that the ground is part of the support system. Self-erecting cranes concentrate load on a small base or ballast area, so a soft patch, a buried service trench or a slope causes settlement or tipping during erection. Candidates also assume a concrete slab is adequate without checking its thickness or reinforcement.
What to do instead
Obtain the manufacturer's ground bearing pressure for the worst erection and operating case, assess the ground by inspection and, where needed, by geotechnical advice, and use load-spreading mats or a designed base sized for that pressure. Confirm there are no services under the base, check level in both directions, and record the check before erection begins.
Erecting, climbing or dismantling the crane without a documented sequence and without controlling the exclusion zone, so that people stand under the jib or in the ballast swing area while the crane is in a partially assembled, unstable state.
Candidates treat erection as a routine assembly task and follow habit rather than the manufacturer's sequence. Partially erected self-erecting cranes are in their least stable condition, and the ballast and jib swing through a wide arc. Candidates also underestimate how quickly a wind gust affects an unballasted or partly assembled crane.
What to do instead
Work to the manufacturer's erection, climbing and dismantling procedure, with a written sequence and a pre-erection briefing. Establish and physically barricade an exclusion zone that covers the full swing of the jib, ballast and any suspended components, post signs, and appoint a person to control entry. Stop work if wind exceeds the manufacturer's erection limit.
Signalling the wrong direction or misreading hand signals, particularly confusing 'hoist up' with 'hoist down', 'slew left' with 'slew right' from the operator's perspective, and using whistle signals that do not match the standard code.
Candidates learn signals visually but never practise them from the operator's seat, where left and right are reversed relative to the signaller's view. Under pressure, candidates also invent signals or use a radio without agreed call signs, and the operator acts on an ambiguous instruction.
What to do instead
Practise the standard hand and whistle signals from the operator's position, and agree before the lift that all directional signals are given from the operator's perspective. Use a single designated signaller, agree radio channel and call signs, and require the operator to stop on any signal that is unclear. Repeat the signal back or confirm by radio before acting.
Skipping or superficially completing the pre-operational inspection and daily check, signing the checklist without physically testing the limiters, brakes and emergency stop, and not reporting a known defect before starting work.
Candidates treat the checklist as paperwork and tick items from memory. They also fear that reporting a defect will stop the job, so they record 'OK' for a function they have not tested. Limiters and brakes are the last line of defence against overload and runaway load, so an untested limiter is an unknown risk.
What to do instead
Carry out the daily check physically, function-testing the hoist, slew and trolley brakes, the moment and maximum load limiters, the height and radius limiters and the emergency stop, and record the actual result. Report any defect immediately, tag the crane out of service if the defect affects safety, and do not operate until it is rectified and the rectification is recorded.
Slinging a load with the sling legs at too wide an angle, or with the load's centre of gravity off the hook, so that the sling's effective capacity is reduced and the load tilts or the sling is shock-loaded when the crane takes up the load.
Candidates use the sling's vertical rated capacity regardless of the included angle between legs, and they judge the centre of gravity by eye. A wide leg angle multiplies the tension in each leg, and an off-centre load causes one leg to take most of the weight and the load to swing when lifted.
What to do instead
Keep the included angle between sling legs within the manufacturer's limit, typically 90 degrees or less, and use a spreader beam where a wider angle is unavoidable. Identify the centre of gravity before slinging, position the hook directly above it, use a test lift of a few centimetres to check balance, and adjust the slings before the main lift.
Operating in wind that exceeds the manufacturer's limit, or continuing to lift a large-sail-area load when the wind is rising, without accounting for the load's wind area, the effect of gusts and the crane's own wind limits for operation and out-of-service conditions.
Candidates use a single wind figure and ignore the difference between the crane's operating limit, the load's sail area and the out-of-service limit. A flat panel load acts as a sail and can swing or rotate the load and overload the jib. Candidates also fail to allow for wind increasing with height and for gusts.
What to do instead
Check the manufacturer's wind limits for operation and for out-of-service parking, measure wind at the crane with an anemometer, and reduce the limit for loads with a large sail area. Stop lifting when the limit is reached, and park the crane in the specified out-of-service condition with the jib free to weathervane. Monitor the forecast before planning the lift.
Relying on a general knowledge of tower cranes rather than the specific licence, registration, inspection and record-keeping obligations that apply to the self-erecting crane and its operator, and not knowing who may erect, alter or dismantle the crane.
Candidates mix up the duties of the operator, the person with management control, the crane owner and the competent erection team. They also assume the operator's licence covers erection and dismantling, or that a pre-operational check substitutes for the required periodic inspection and maintenance records.
What to do instead
Learn the separation of duties: the operator operates, a competent person inspects, and erection, climbing and dismantling are done by a competent team under a documented procedure. Know the record-keeping obligations for inspections, maintenance, defects and training, and know the circumstances in which the crane must be taken out of service and reported.
Assuming a self-erecting tower crane is stable because it has a ballast block, and ignoring the stability triangle, the effect of slew and travel on tipping, and the need to keep the crane level and free of side pull during the lift.
Candidates conflate 'ballasted' with 'cannot tip'. Self-erecting cranes rely on a combination of ballast, base width and outrigger spread, and the stability margin is reduced by side pull, by travelling with a suspended load, by an unlevel base and by wind. Candidates also forget that the crane's own jib and counterweight contribute to the overturning moment.
What to do instead
Understand the stability triangle or base footprint, keep the crane level within the manufacturer's tolerance, and never drag or side-pull a load. Travel only as the manufacturer permits, with the load lowered and controlled, and re-check level after any movement. Treat every lift as a stability calculation, not just a capacity check, and keep the counterweight and ballast as specified.