High Risk Work Licence - Slewing Mobile Crane C2 (20t) common mistakes
High Risk Work Licence - Slewing Mobile Crane C2 (20t) · Understand the traps and how to avoid them.
Treating the rated capacity on the load chart as the true limit for a lift, without deducting the mass of hook block, slings, shackles, spreader beams and other lifting gear from that figure.
Candidates memorise the load chart number as 'the capacity' and mentally picture only the payload, forgetting that gross load determines structural and stability limits. Under exam pressure they also confuse net and gross capacity terminology.
What to do instead
Practise reading charts by calculating gross load every time: payload plus rigging plus hook block, then compare with the chart value at the actual radius. Learn the definitions of rated, gross and net capacity and work several example calculations until the deduction step becomes automatic.
Reading the load chart at the boom length or radius the candidate intended rather than the radius that actually applies, such as measuring radius to the load's near edge or ignoring boom deflection and load swing.
Candidates treat radius as a simple tape measurement from the slew centre and forget it is the horizontal distance from the slewing axis to the centre of gravity of the load, measured with the boom at working position and the load hanging freely.
What to do instead
Revise the formal definition of working radius, then practise setting up scenarios: identify slew centre, mark the load's centre of gravity, account for boom deflection when loaded and for the load swinging out during slewing. Confirm the chart row for the actual boom length and configuration before accepting a capacity.
Assessing ground conditions by eye and setting up without verifying bearing capacity, without proper mats or outrigger pads, and without checking for voids, services, backfilled trenches or recent excavation near the outrigger positions.
Familiar sites look 'solid' and candidates skip the step under time pressure; many have never seen a crane overturn or an outrigger punch through a slab, so the risk feels theoretical. They also do not know how to use outrigger load data.
What to do instead
Follow a fixed setup checklist: obtain or estimate outrigger loads from the manufacturer's data, inspect the whole footprint for fill, drains, basements and services, use purpose-made pads sized to spread the load, and re-check after the crane is levelled. Learn to state the consequence of inadequate bearing capacity in terms of stability and structural failure.
Rigging loads without confirming sling angle effects, without calculating the increased tension in each leg as the included angle widens, and without checking the load's centre of gravity and balance point before lifting.
Candidates use 'rule of thumb' multipliers inaccurately or ignore them, and they judge balance visually. Sling angle tension and centre-of-gravity behaviour are the parts of rigging most often learned superficially.
What to do instead
Learn the leg-tension relationship for 60, 90 and 120 degree included angles and the resulting load multiplication, and practise calculating share of load per leg for symmetric and asymmetric arrangements. Always identify the centre of gravity and plan the attachment points and tag lines before the lift.
Performing a pre-operational inspection as a box-ticking ritual, missing items such as wire rope broken wires, kinking, corrosion and end fittings, hook latch and throat opening, brake and limit switch function, outrigger beam and jack condition, and safety device operation.
Candidates have seen the checklist so often they recite items without knowing what a reject criterion looks like, and they cannot distinguish a defect that requires shutdown from one that can be monitored.
What to do instead
Study defect criteria for each component and learn to state them numerically where standards specify them. Rehearse a walk-around in a fixed sequence, and for each item be able to say what 'unserviceable' looks like and what action follows. Practise explaining why a defective limit switch or brake makes the crane unfit for use.
Relying on hand signals or verbal communication alone in a noisy or blind-lift situation, without a designated dogman, agreed signals, radio protocol or a plan for loss of communication.
Candidates underestimate how easily signals are misread at distance or in poor light, and they have not been taught that only one person should give signals at a time or what to do when a signal is ambiguous.
What to do instead
Learn the standard hand and whistle signals and the radio call protocol, including the stop signal that overrides all others. In answers, always nominate a single designated signal person, agree signals and radio channel in a pre-lift briefing, and state that an unclear or lost signal means stop and make safe.
Answering hazard and risk questions with generic statements such as 'assess the risk' or 'be careful' instead of identifying specific hazards, their sources, likelihood and consequence, and a control that follows the hierarchy of control.
Candidates confuse describing an outcome with controlling a hazard, and they have not practised structuring a risk assessment answer. They also list controls in arbitrary order rather than eliminating or engineering out the risk first.
What to do instead
Practise a repeatable structure: hazard, who is exposed, existing controls, risk rating, additional control, residual risk. For each scenario, name at least one elimination or engineering control before administrative or PPE controls, and give a concrete action rather than an attitude.
Describing emergency procedures as 'lower the load and call the boss', without a sequenced response for power failure, brake failure, load drift, fire, contact with overhead lines, or a person injured in the work area.
Emergency content is often studied last and superficially, so candidates know the existence of procedures but not the order of actions, the isolation steps, or who has authority to declare an emergency.
What to do instead
Build a short script for each credible emergency: stop and secure the load, warn and exclude people, isolate or shut down as appropriate, notify according to the site plan, and preserve the scene for investigation. Learn the specific hazards of overhead line contact, including staying in the cab and the step-and-shuffle exit where applicable, and rehearse the shutdown sequence.
Confusing the licence class and its conditions, or being unable to state the duty-of-care obligations of the crane operator, dogman and site controller, and the role of the safety observer near overhead lines.
Legislative content is memorised as isolated phrases rather than understood as a chain of responsibility, so candidates mix up who must hold which licence, what a high risk work licence permits, and when a safety observer is mandatory.
What to do instead
Map each duty to the role that holds it: operator, dogman, rigger, safety observer, site supervisor. Learn the licence class limits for this crane type, the requirement for a safety observer near energised lines, and the primary duty to ensure health and safety so far as reasonably practicable, then test yourself by explaining each duty in one sentence.
Skipping post-operational requirements: parking and securing the crane, lowering and stowing the boom, applying slewing and travel brakes, isolating power, removing the key, and recording defects or incidents in the maintenance log.
The task feels finished when the last load is landed, and candidates treat shutdown as housekeeping rather than a safety and legal record-keeping obligation, so they omit defect reporting and log entries.
What to do instead
Memorise a fixed shutdown sequence and the reason for each step, including why the boom is lowered and the crane left in a stable, out-of-service condition. Practise writing a short defect or incident entry that states what was found, when, and what action was taken, and note who must be informed.