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What is a critical lift?

Per BS 7121 / OSHA, a critical lift is one where the capacity utilization is 75% or higher, or any lift over live process plant, or a tandem dual crane lift. Critical lifts require an Appointed Person (AP) sign-off before execution.

How is sling leg tension calculated?

Sling Leg Tension = (Total Gross Load / Number of Legs) × (1 / sin(Sling Angle)). For example, a 20-ton load on 4 legs at 60° gives 20/4 / sin(60°) = 5.77 tons per leg. Always verify the shackle WLL safety factor is ≥ 2:1.

How is outrigger mat size determined?

The maximum outrigger pad load (worst case 50% of gross load on one side, dynamic factor 1.2×) is divided by the soil bearing capacity. Compacted gravel ≈ 200 kN/m², concrete ≈ 500 kN/m², uncompacted soil ≈ 100 kN/m².

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AP Lifting Plan & Capacity Calculator

Per BS 7121 / LOLER / OSHA 1926.451 — Multi-Page PDF Package with 2D Elevation

Project

Load

Crane

Rigging & Site

Project & Location Data

Project Name

Client

Site Location

Document Reference

Lifting Category

Sign-Off Roster (for PDF)

Appointed Person (AP)

Lift Supervisor

Crane Operator

Client HSE Rep

Step 1 of 4

The crane lifting plan calculator generates a complete Appointed Person (AP) lift plan package per BS 7121, LOLER, and OSHA 1926.451. It computes gross load, capacity utilization, sling tension, outrigger bearing, and wind limits, then exports a 3-page PDF with 2D elevation sketch, execution procedure, and sign-off roster. This tool is designed for lift planners, appointed persons, and HSE engineers managing crane operations.

Gross Load and Capacity Utilization

The total gross load = Net Load + Spreader Bar Weight + Hook Block Weight. Capacity utilization = Gross Load / Rated Capacity at the working radius, expressed as a percentage. Below 75% is a standard lift. At 75% or above, it becomes a critical lift requiring AP sign-off. Above 90%, the crane must be reconfigured — the lift is unsafe.

Sling Tension and Safety Factors

Sling leg tension = (Gross Load / Number of Legs) / sin(Sling Angle). For a 20-ton load on 4 legs at 60°: 20 / 4 / sin(60°) = 5.77 tons per leg. The shackle safety factor = Shackle WLL / Sling Tension. A minimum of 2:1 is required. If the safety factor is below 2:1, a larger shackle is needed. The calculator flags this automatically.

Outrigger Ground Bearing

Worst case: 50% of gross load on one side, split across 2 outrigger pads.
Dynamic factor of 1.2× applied for lifting motion.
Required mat area = Outrigger Load / Soil Bearing Capacity.
Compacted gravel: 200 kN/m². Concrete slab: 500 kN/m². Uncompacted soil: 100 kN/m².
The calculator recommends the minimum square mat size in millimeters.

Critical Lift Criteria

A lift is classified as critical if: capacity utilization is 75% or higher, the lift is over live process plant, it involves tandem (dual crane) lifting, or the load is irreplaceable/hazardous. Critical lifts require an Appointed Person (AP) to sign off the lift plan before execution. The PDF includes a complete sign-off roster for the AP, lift supervisor, crane operator, and client HSE representative.

Environmental and Site Controls

Wind speed must not exceed 9.0 m/s (per BS 7121 default) — the calculator flags if the entered value exceeds this. Overhead powerline clearance must be at least 6 m. Underground utilities must be identified before crane setup. The execution procedure in the PDF includes a 100 mm trial lift protocol: lift the load 100–200 mm off the ground, hold for 2 minutes, check stability and sling tension, then proceed.

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