Scissor lift on a suspended slab
A 26 ft electric scissor lift is being used inside a new warehouse to install sprinkler pipe. The slab is a suspended post-tensioned deck with a stated live load of 100 psf. The lift weighs 5,200 lb, and its wheel footprint is 7 ft by 4 ft. Two workers (350 lb total) and 300 lb of pipe and tools are on the platform. The lift must be driven within 1.2 m of an unguarded floor opening; the opening is covered with plywood marked ‘do not load.’ The route crosses a construction joint with a 20 mm lip. The site has no spreader mats, and the supervisor says ‘the slab is designed for forklifts.’ The platform is currently at 9 m height with the pipe bundle resting on the mid-rail.
1. Assess the floor loading and decide whether the lift can operate on the suspended deck.
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Total imposed load is 5,200 + 350 + 300 = 5,850 lb. Over the 7 ft × 4 ft = 28 sq ft footprint, that is about 209 psf average, already more than double the 100 psf live-load rating. The wheel loads are much more concentrated than the average, so the slab could be punched even if the average looked acceptable. The supervisor’s ‘forklift’ comparison is not an engineering check; forklifts have different axle loads and the slab may have been designed for specific routes. Without spreader mats and a written structural check, do not operate on the suspended deck. Options are a lighter lift, a ground-level lift, or an engineered load-spreading platform with the engineer’s approval. The plywood cover is not a load-bearing surface and must not be driven over.
2. Evaluate the proposed route near the floor opening and over the construction joint.
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Keep at least the designed clearance from the unguarded opening; 1.2 m is not enough for a lift that can move or for operator error. The opening should have a rated cover or a guardrail, and the plywood marked ‘do not load’ is a warning, not a cover. The 20 mm lip at the construction joint can cause a wheel to climb or the chassis to twist; cross slowly at right angles, never travel elevated over it, and check the manual for the maximum step. If the lift cannot cross safely, bridge it with a rated ramp or choose another route. Barricade the opening and the joint, and keep the lift’s wheels away from the cover.
3. What controls and records would make this task acceptable if an engineer approved it?
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Controls: written engineer’s approval for the slab and route; spreader mats sized to wheel loads; barricades and signage at the opening; a planned route that avoids covers and the joint; a pre-use inspection including tyre condition and battery charge; a rescue plan for the deck. Fall protection: guardrails are the primary means on a scissor, but the risk assessment may require a harness and short lanyard if the guardrail is incomplete or the operator must lean out; never tie off to the lift unless the manufacturer provides an anchor. Record the approval, load calculation, mat size, inspection, and briefing. Stop if the slab cracks, deflects, or the lift alarms.