Boom lift beside a deep excavation
A 45 ft articulated diesel boom lift is positioned beside a 3 m deep excavation on a residential site. The manufacturer’s platform capacity is 500 lb, and the operator plans to carry two workers (200 lb each) plus 80 lb of tools. The ground is compacted fill, but the side slope reads 4° on the chassis inclinometer; the manual’s maximum side slope for elevation is 5°. A spoil pile sits 2.5 m from the trench edge, and the nearest outrigger would be placed 1.8 m back from the edge. Wind is 18 km/h with 30 km/h gusts. The operator wants to slew the platform over the trench to reach a fascia board, and the site supervisor says the trench is ‘only shored at the bottom.’
1. Calculate the platform load and decide whether the lift can be elevated as planned. Show the reasoning that would justify your decision.
Read the worked answer
Platform load is 200 + 200 + 80 = 480 lb, which is 96% of the 500 lb rating. That is technically within capacity, but it leaves only 20 lb margin and no allowance for slings, sealant, or wind load on the workers and tools. More importantly, capacity is not the deciding issue: the outrigger would be 1.8 m from a 3 m deep excavation, within the zone where outrigger pressure can reduce trench stability. A common rule is to keep foundations back from an excavation by at least its depth, and often more; 1.8 m is less than 3 m. The 4° slope is inside the 5° limit, but only if the inclinometer is reading chassis level and all outriggers are on firm, equal-bearing ground, which is not established. The 30 km/h gust also needs checking against the manual. Decision: do not elevate over the trench. Relocate the lift to a verified firm area, obtain an engineer’s assessment for the trench edge, or use a different access method.
2. What specific actions would you take before any outrigger is deployed, and what would you record?
Read the worked answer
Before deploying any outrigger: confirm underground services and voids; mark the excavation edge and establish a barrier; move the spoil pile back; calculate the outrigger load and size spreader pads from the load chart and ground bearing; check that the obstruction is clear; deploy all outriggers fully, level the chassis, chock wheels, and confirm the inclinometer is within the manual. If the ground is compacted fill, test or inspect it; do not assume. Record the pre-use inspection, ground condition, pad size, outrigger load calculation, wind reading, load calculation, and any engineer’s written approval. The supervisor’s verbal assurance is not a record. If any item cannot be verified, stop.
3. The boom loses power with the platform 9 m high over the trench. Describe a safe recovery sequence.
Read the worked answer
Keep the platform occupants in place, secure controls, and establish communication. Do not climb the boom or jump. Use the manufacturer’s emergency lowering procedure from the ground controls if reachable, or the platform auxiliary controls if trained. Lower the boom first by retracting or raising to bring the platform over safe ground, not over the trench, then lower to a safe landing. If the platform cannot be moved clear, call the site emergency plan and fire/rescue; do not attempt a makeshift rope rescue. Barricade the area, keep the trench exclusion zone, and record the incident. After recovery, the lift must be inspected before reuse.