Near-Capacity Panel Lift With Sail Area and LMI Warning

The suspended load is 3.0 t plus 0.12 t of rigging, or 3.12 t. At 45 m the chart allows 3.4 t, so the static utilization is about 92 percent. That is already a small margin, but the critical point is that the crane must move 10 m farther out, to about 55 m. Tower crane capacity falls with radius; the chart value at 55 m must be checked and may be below 3.12 t. The rigger is comparing the load to the wrong radius and ignoring the planned travel. The rigger also treats the LMI as overly conservative, but the LMI is measuring actual moment, including the load, trolley position, and jib geometry. At 94 percent, only about 6 percent margin remains, and that margin can be consumed by wind on the 18 m² panel, load sway, tag-line forces, and dynamic effects when starting or stopping trolley and slew. A panel acts as a sail and creates side load and additional moment, especially at a long radius. The correct evaluation uses the final radius chart, total suspended load, wind limits, and the manufacturer's guidance on sail-area loads. If any value is unknown, the lift is not cleared.

When the LMI alarms, the operator should stop the dangerous motion, not push through it. The operator should hold the trolley, reduce radius if the procedure allows, and lower the load only if it can be done safely without increasing moment. The LMI is a safety device, not a suggestion; overriding or ignoring it removes the crane's last automated protection against overload. The rigger's 'set conservative' comment should be rejected because the device is calibrated to the crane's load chart and geometry, and the observed 94 percent is consistent with a near-capacity condition. The crew should treat the alarm as information that the lift plan is no longer valid. The supervisor and lift director should be called, the final radius chart should be checked, and the load should be set down in a safe location if it is already suspended. No one should stand under the panel while it is held. If the chart at the final radius cannot support the load with adequate margin, the lift must be re-planned with a different crane, a different panel breakdown, or lower wind conditions. The operator has the authority and duty to refuse the move.

A safer plan starts by eliminating the long-radius near-capacity move. Options include repositioning the crane, using a larger crane, lifting the panel in smaller sections if engineering allows, or waiting for wind to drop and verifying the chart at the exact final radius. The panel should be weighed or its weight verified, and the rigging weight included. A pre-lift meeting should cover the route, the final radius, wind monitoring, tag-line placement, and the abort criteria. The tag line should be controlled by a rigger who remains in a safe position and, critically, the signal person must be in clear view of the operator or in reliable radio contact. The rigger at the building corner out of view is not acceptable as the only signal source. A qualified signal person should be positioned where the operator can see the load and the landing area, with a backup radio channel and agreed signals. The landing area should be barricaded, and the panel should not be slewed over occupied space. If the LMI approaches its threshold again, the operator stops and the lift is re-evaluated.