8.3 Lift Planning, Load Charts, Sling Angles and Crane Signalling

The lifting plan

Regulation 15(2) of the Plant Requiring Certificate of Fitness Regulations 2024 requires the owner or occupier to establish a lifting plan, taking into account the risk assessment report, so the tower or mobile crane can be operated safely. The CDM 2024 construction phase plan should say how lifting is planned and controlled. Lifts involving heavy prefabricated components are Fourth Schedule particular-risk work.

Who is involved

Roles in the widely used British code BS 7121 (safe use of cranes):

The SSS audits the plan and checks on site that the lift matches it.

Contents of a lift plan

1. The load: weight from documents or calculation, centre of gravity, lifting points, dimensions, fragility.
2. The crane: type and configuration (boom length, counterweight, outrigger extension), certificate of fitness, operator.
3. Radius and capacity: maximum radius during the lift, including slewing and placing; capacity from the duty chart; percentage utilisation.
4. Ground and set-up: ground bearing pressure under the tracks or outriggers; mats; distance from excavations and slopes.
5. Tackle: slings, shackles, spreader beams and their ratings; sling angle; weight of tackle.
6. Environment: overhead lines (CDM regulation 27), structures, other cranes, public areas; wind speed limits; lighting.
7. Exclusion zones: barricades below the load path and around the counterweight's slew.
8. Communication: signaller, radio channel, hand signals; blind lifts.
9. Sequence and contingencies: step-by-step method; what happens if the load sticks, the wind rises or a fault occurs.
10. Emergency arrangements: rescue and first aid, including a crane cab emergency.

Many sites use categories:

• basic: a routine lift in good conditions, using a generic plan
• standard: a specific plan
• complex: tandem lifts, lifts near power lines, heavy precast, or lifts above about 75–80% of capacity, needing an engineered plan and senior sign-off

Define the categories in the site lifting procedure.

Reading a duty (load) chart

A crane's rated capacity depends on its configuration and on the radius, the horizontal distance from the centre of rotation to the hook. Capacity falls quickly as radius increases.

Rules for using the chart:

• Use the chart for the exact configuration: boom length, counterweight, outriggers fully extended or not, and the slewing area (over the rear, side or front).
• Use the maximum radius reached during the lift, including where the load is placed. Slewing and the booms bending under load increase the radius.
• Deduct from the chart capacity the weight of the hook block, slings, shackles and spreader beams, and any stowed jib if the manufacturer requires.
• Do not interpolate unsafely between values. Use the next greater radius or the next shorter boom.
• The rated capacity limiter (safe load indicator) supports the operator but does not replace planning. Never override it.

Worked example. A precast panel weighs 6.8 t. The hook block and tackle weigh 0.4 t, so the total load is 7.2 t. At the planned 18 m radius, with the boom length chosen, the duty chart shows 8.0 t for this configuration over the side.

Utilisation is 7.2 / 8.0 = 90%. That is too close for a wind-sensitive panel lift. The planner moves the crane to reduce the radius to 15 m, where the chart shows 10.5 t. Utilisation becomes 7.2 / 10.5 = 69%.

Sling angles and leg tension

When slings are not vertical, each leg carries more than its share of the load. For a sling with n equally loaded legs, each at angle θ from the vertical, the tension in each leg is:

$$T = \frac{W}{n \cos\theta}$$

At a 120° included angle, each leg carries a tension equal to the whole load, twice the vertical case. Many lifting codes and manufacturers limit multi-leg slings to an included angle of 90° for normal rated use, and treat 120° as an absolute maximum. Keep sling angles narrow by using longer slings or a spreader beam.

Worked example. A 4.0 t load is lifted with a two-leg chain sling at a 60° included angle (θ = 30°):

$$T = \frac{4.0}{2 \times \cos 30^\circ} = \frac{4.0}{2 \times 0.866} = 2.31\ \text{t per leg}$$

Check the chain sling's tag. Multi-leg slings are rated at stated angle ranges, typically 0–45° and 45–60° from vertical, and the rated capacity at the actual angle must exceed the load.

Remember also:

• Choke hitches reduce a sling's capacity, typically to about 80% for many slings. Use the manufacturer's mode factors.
• Basket hitches can increase capacity only if both legs are vertical and the load is balanced.
• Uneven legs or an offset centre of gravity put more load on one leg than the formula assumes.

Signalling and communication

• One signaller directs the crane at a time, and is identified clearly, for example by a coloured vest. Anyone may give the emergency stop.
• Use standard hand signals, such as those in ISO 16715 or BS 7121, agreed and briefed before the lift. Common signals:
  • Hoist: arm raised with forearm vertical, index finger pointing up, making small horizontal circles.
  • Lower: arm extended down, index finger pointing down, making small horizontal circles.
  • Stop: arm extended horizontally, palm down, held still.
  • Emergency stop: both arms extended, palms down, moved quickly back and forth.
  • Slew: arm extended pointing in the direction of slew.
  • Move slowly: one hand placed motionless over the hand giving the signal.
• Radio: dedicated channel, identification at the start of each message, continuous communication during blind lifts, and an agreed signal for loss of contact, which means stop.
• The operator must stop if signals are unclear, if communication is lost, or if anyone enters the danger zone.
• Blind lifts, where the operator cannot see the load, need a signaller with a clear view of both the load and the operator, or a relay of signallers using radio, set out in the plan.

Scenario: the tandem lift that wasn't planned

Two mobile cranes are about to tandem-lift a 22 m steel girder. The "plan" is a sketch with no individual crane loads, the girder's centre of gravity is unknown, and one crane's operator is using a different radio channel. The SSS halts the lift because:

• a tandem lift is a complex lift
• each crane's share of the load changes as the girder tilts or the cranes move
• the regulation 15(2) lifting plan must be based on a proper risk assessment

The lift resumes only after an engineered plan:

• the girder's weight and centre of gravity are calculated
• each crane is limited to a reduced percentage of its capacity
• spreader beams keep slings vertical
• the radio channel is shared and the lift supervisor is named
• wind limits and an exclusion zone are set
• both operators record their limit switch tests before starting