Overload Alarm Before the 18/F Concrete Pour
A builder's lift cage is rated at 2,000 kg or 20 persons. At ground level, the site agent wants to send 8 workers, two wheelbarrows of mortar estimated at 300 kg each, and a 950 kg concrete skip to 18/F in one trip. The operator's load display shows 2,150 kg before the cage door is closed, and the overload alarm sounds. The agent says the load cell is 'always a bit high', asks the operator to reset the alarm and continue because the concrete pour is waiting. The wind is gusting and the cage floor is wet. The load chart is fixed inside the cage and the counterweight is correct for the mast height.
1. Calculate the load situation and decide what the operator should do. Show your reasoning.
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The declared load is already above the rated capacity. Eight workers at a planning figure of 75 kg each is 600 kg; two wheelbarrows at 300 kg each is 600 kg; the skip is 950 kg. The total is 2,150 kg, which is 150 kg over the 2,000 kg rating before any allowance for dynamic effects, load distribution or the wet cage. The overload alarm is therefore correct, not a nuisance. The operator should not reset it. He should require the load to be reduced to well below 2,000 kg, not exactly to the limit. A practical approach is to send the skip on one trip and the workers with the barrows on another, or to reduce the number of workers and split the materials. The load should be distributed so that it is not concentrated on one side of the cage floor. The operator should check the load display after offloading and confirm that the alarm clears before moving. If the alarm persists with a known light load, the overload device is defective and the hoist should be taken out of service.
2. Why must the overload alarm not be reset or bypassed, and what factors make this trip more critical than the display alone suggests?
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The overload device protects the mast, ties, cage structure, hoist unit and brakes. A cage rated at 2,000 kg has a margin for normal dynamic loads, but that margin is not permission to run at or above the limit. Starting, stopping and landing produce dynamic forces greater than the static load, and a wet, gusty situation makes the cage harder to control and increases the chance of a sudden snatch. The load is also poorly distributed: a heavy skip and a group of workers can put an eccentric load on the cage and mast. Resetting the alarm does not remove the load; it only removes the warning. If the operator resets and the alarm is faulty, he has no protection. If the alarm is correct, he is knowingly running an overloaded hoist. Either way, the safe decision is to offload. The agent's claim that the load cell is 'always a bit high' is not evidence; the operator should use the rated load and the load chart, not the agent's opinion.
3. How should the operator communicate the decision and record it?
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The operator should explain the arithmetic briefly and firmly: 2,150 kg against a 2,000 kg rating, so the trip cannot proceed. He should propose a safe alternative, such as two trips with the skip separated from the workers and barrows. He should not enter a debate about the load cell; if the agent disputes it, the operator can ask for the hoist to be checked by a competent person, but the hoist stays stationary meanwhile. The refusal and the reason should be entered in the log book with the time, the displayed load, the alarm condition and the names of those present. The agent's instruction should be recorded factually. If the agent tries to remove passengers only and keep the skip, the operator should recalculate and confirm the new load. If the alarm sounds again with a load that is clearly within rating, he should stop and report a defect rather than assume the display is wrong.