Planning and Performing Lifts, Including Multi-Crane and Critical Lifts
The lift plan
A lift plan documents the load, mass, radius, configuration, chart capacity, rigging, ground conditions, personnel, controls, sequence and contingencies. Critical lifts, such as those over occupied areas, near powerlines, with tandem or multi-crane arrangements, or with unusual loads, demand a higher level of engineering and approval. A lift study may be prepared by an engineer.
Multi-crane lifts
Multi-crane lifts are high risk and should be avoided where possible. When unavoidable, each crane's share must be calculated for the actual geometry, allowing for load transfer as the load is raised, moved and lowered. The load's centre of gravity should sit between the hooks, and the plan must address what happens if one crane loses capacity or the load shifts. Use a single nominated person in control, agreed signals and a rehearsed sequence. De-rate for the angle of the slings and for unequal load sharing; assume the worst realistic distribution.
Performing the lift
Conduct pre-lift checks, confirm the exclusion zone, test the load just clear of the ground, check the brake, then proceed. Monitor radius, wind, load swing, ground and personnel. Stop if anything changes. Use taglines to control rotation, never to take load.
Traps
Questions reward recognising that a two-crane lift does not simply halve the load. Also watch for "the load is under capacity so it is safe" and for ignoring wind on a large sail area.
Rule of thumb
For multi-crane lifts, plan each crane to no more than about 75 percent of its rated capacity for the geometry, and never assume equal sharing.