Construction hoist with a bypassed interlock
A rack-and-pinion construction hoist has two cages, each rated 2,000 kg. At the ground landing, nine workers (average 80 kg) and a 1,000 kg pallet of blocks are waiting. The cage floor is 3 m by 1.5 m. The pallet is loaded to one side, and the landing door interlock on the upper landing has been bypassed with a cable tie because the door is stiff. Wind at the top landing is 40 km/h; the hoist manual says operation should stop when wind exceeds 20 m/s. The trained operator has gone for lunch, and a labourer holds the key. A load chart inside the cage shows a maximum of 12 persons, but it also requires loads to be evenly distributed and secured. The upper landing is 28 m above ground.
1. Calculate the proposed cage load and decide whether the cage can be loaded as planned.
Read the worked answer
Nine workers at 80 kg = 720 kg; plus the 1,000 kg pallet = 1,720 kg. That is below the 2,000 kg cage rating, but the rating is not the only check. The pallet is loaded to one side, so the cage floor and guide rollers see an eccentric load; the load chart requires even distribution and securing. A 1,000 kg pallet on a 3 m × 1.5 m floor is also a local point load, and the workers would be standing around an unsecured load. Mixed passenger and material loads may be prohibited or restricted by the manual. The correct decision is to split the load: send the pallet as a material run with a trained operator, or distribute and secure it, and keep workers clear. Do not rely on total weight alone.
2. What must be done about the bypassed landing-door interlock and the untrained key holder?
Read the worked answer
The interlock is a safety device that prevents cage movement with a landing door open. A cable tie bypass defeats it, and someone can fall from the landing or be struck by the cage. The hoist must be stopped, the key controlled, and the door repaired and tested. The upper landing must be barricaded and the fault recorded. Do not use the cage with the bypass, even if the other cage is available, unless the defective cage is isolated and locked out. The labourer holding the key is not a trained operator; the key must be returned to the trained operator or the supervisor. This is a reportable defect, not a minor inconvenience.
3. Assess the wind and load-security issues if the correct operator returns and the interlock is repaired.
Read the worked answer
40 km/h is about 11.1 m/s, below the manual’s 20 m/s stop, so wind alone does not stop this lift, but it is still a factor: the pallet presents a sail area, and wind at the top landing can be stronger than at ground. Check the manual for any lower wind limit with the load and height, and secure the pallet. The bigger issues are the interlock bypass and the untrained key holder. The labourer must not operate; wait for the trained operator. If the load is carried, keep it balanced and secured, keep persons out of the cage except the operator, and use the other compliant cage if possible. Record the wind reading and the load plan.