Three Weeks of Rain, One Loose Earth Lug, and a Sling With a Bad Tag
Monday, 06:10. A 10 t flat-top tower crane with a 55 m jib has been standing for three weeks on a 6 m x 6 m x 1.4 m raft foundation at a mid-rise condominium site. Overnight rain of 38 mm has left about 40 mm of standing water in the foundation recess around the mast. The four anchor bolts above the grout show brown rust streaks that were not there on Friday. The mast earth conductor is hanging loose at its lug on the base section; the earth rod itself is intact and was tested at handover. Today's first lift is a 3.2 t precast wall panel, using the rigging crew's 4-leg chain sling: one leg has a twisted, visibly deformed link, and the inspection tag reads 'last examined 14 months ago' against a site rule of six months. The crane's third-party monthly certificate is current. The daily checklist sheets for Friday and for this morning are blank. The site supervisor says to pump out the water and start, because the concrete has had three weeks to cure.
1. Sort the findings into stop-work, correct-before-use, and monitor, and justify each classification.
Read the worked answer
The dividing line is whether the defect can degrade the crane's ability to hold the load or to resist a predictable force.
Stop-work until cleared
- Earth conductor loose at the lug. This is the finding that cannot be argued with. A tower crane is the tallest steel structure on most sites. Without a continuous low-resistance path to the earth rod, a strike on the jib or an insulation failure on the site's temporary supply can raise the potential of the mast and the cab while the operator is inside it. Re-terminate to the manufacturer's torque, then have continuity or resistance measured and the result recorded before the crane is energised.
- Rust streaks on the anchor bolts. Standing water by itself is cosmetic. New corrosion on the anchor bolts is not, because the bolts are the load path from mast to foundation and they become uninspectable once grouted. Hold the crane pending a check by the crane or structural engineer, and pump and drain the recess in the meantime.
Correct-before-use
Complete Friday's and today's daily checklists. An unsigned sheet is not a formality: it means there is no record that the previous shift found the machine fit, and any defect that developed over the weekend has gone unlogged.
Monitor
The raft itself, for fresh cracking or differential settlement, for the duration of the hold.
2. What do you do with the chain sling and its tag, and what must the replacement satisfy?
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The sling fails on two independent grounds, and either one is sufficient.
First, a twisted and deformed link is mechanical damage. A link that has been deformed has been overloaded or badly handled and no longer has a known capacity; the deformation is the evidence, so you do not need to test it to condemn it.
Second, the examination interval. The site rule is six months; the tag says 14. That tag is not evidence of fitness, it is evidence of a missed inspection - and this crew has been picking with it for eight months past due.
So: remove it from service, fit a dated 'DO NOT USE' tag to the master link where it cannot be pulled off a leg, and move it to the quarantine cage - not back onto the rigging truck, where someone will reach for it tomorrow. Record the withdrawal in the rigging register and tell the rigging supervisor the same morning.
Then replace, do not substitute. The replacement needs a legible tag within six months, an ID traceable to a test certificate, and a WLL that covers 3.2 t at the angle the legs will actually make on the panel. At 45 degrees to the horizontal, a 4-leg sling rated 2 t per leg gives roughly 3 x 2 x 0.707, about 4.2 t, which covers the panel - but only if the legs are dressed properly and the panel's lifting points are symmetric. Verify the angle with the panel just clear of the ground, not before.
3. How do you respond to the supervisor's instruction, and what do you record?
Read the worked answer
The instruction does not change what the equipment is doing. The 'three weeks cured' argument answers a question nobody raised: the concrete is not the issue. The anchor bolts, the earthing and the sling are. Say that plainly, then give him a path rather than a flat refusal - a refusal without a plan just invites the same argument tomorrow.
Concretely: the crane stays on hold until the earth conductor is re-terminated and tested, the engineer has inspected the anchor bolts, and a compliant sling is on site. Give him times. Earthing test, 30 minutes. Engineer, two hours. Replacement sling from the yard by 10:00. He can plan around that.
Record it. Enter the defects and the hold in the crane log and the site's out-of-service register with time, names and who was told what, and notify the lifting supervisor and the safety officer the same morning. The record matters twice: it protects the operator if someone quietly overrides the hold, and it is the only evidence of the crane's true condition if there is an inquiry later.
If he insists the crane works anyway, the operator does not start it. Under RA 11058 and its IRR, a worker has the right to refuse work that presents imminent danger - and the operator is the person who will be sitting under the mast.