Trailer-mounted 1B boom near overhead lines
A trailer-mounted 1B boom lift with a 12 m working height is set up on a customer’s asphalt driveway to clean gutters. One outrigger sits on a 0.5 m square patch of soft, recently excavated ground; the other three are on asphalt. The machine’s outrigger load chart shows 2,800 lb per outrigger at full extension. An 11 kV overhead line runs 3.2 m from the nearest edge of the platform at full slew, and the line has no insulating cover. Wind is 20 km/h. The homeowner wants the work done before rain, and the operator has a fibre-glass pole for reaching the gutter. The outrigger pad is 300 mm square and sits directly on the soft patch. The operator has not deployed the fourth outrigger fully because a car is parked in the way.
1. Evaluate the outrigger setup and state what must change before elevation.
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All four outriggers must be fully deployed on ground that can carry the load. The chart load is 2,800 lb per outrigger. A 300 mm square pad has an area of 0.09 m²; 2,800 lb is about 1,270 kg, so the pressure is about 14,100 kg/m², or roughly 138 kPa. That is too high for soft recently excavated ground, and the pad is too small. Use a spreader pad or cribbing sized for the actual ground bearing, or excavate and compact, or relocate. The fourth outrigger cannot be left partly retracted because a car is in the way; the car must be moved, or the lift cannot be used. Level the chassis within the manual and check the outrigger indicators. Record the pad calculation and ground condition.
2. Assess the overhead-line risk and decide whether the gutter work can proceed.
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At 3.2 m from an 11 kV line, the platform is already close to typical minimum clearance zones, and the line has no insulating cover. The risk is not just the static distance: boom movement, wind sway, line sag, and the operator’s reach can reduce it. A fibre-glass pole does not make the task safe and may bring the operator closer. The correct decision is to stop unless the utility has confirmed isolation or the site has a permit and barriers that keep every part of the platform and its load at the required distance. If work must proceed, use a spotter, barrier goalposts, and a documented safe system; do not rely on the homeowner’s urgency. Rain would also increase conductivity and should stop the job.
3. An outrigger starts to sink while the platform is raised. Describe the immediate response.
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If an outrigger sinks or the chassis alarms: stop all platform movement, lower the boom to a safe position, and do not try to level the machine with people in the platform. Use the emergency lowering procedure to bring the platform to the ground, then retract the outriggers only after the platform is secured. Evacuate and barricade. If the machine is unstable, call a competent person and do not re-enter. Record the ground failure and have the lift inspected before reuse. The key is to reduce the height and load first, not to chase the outrigger with cribbing under a raised platform.