Lifting incident during rooftop AHU replacement: notifications, causation and controls
At a hospital redevelopment site in Kowloon, an 1,800 kg rooftop air-handling unit was being lifted 3 m by a 2 t chain block suspended from a rolled-steel purlin that no structural engineer had checked. The lift plan was a hand sketch; no shackle was used at the purlin and the top hook was hooked over the flange; the signalman was also acting as banksman. Two workers stood beneath the load to steady it. As the unit was slewed, the hook slipped off the flange and the unit fell, striking one worker's leg and fracturing his femur, and narrowly missing another. The chain block's periodic examination certificate had expired four months earlier. The site safety officer had raised the absence of a lifting plan two weeks before in the weekly meeting minutes. The subcontractor's supervisor says the workers should have known not to stand underneath.
1. Set out your immediate actions and the statutory notifications.
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Immediate actions (first hours)
- Stop the lift and all work in the area; make the load and the purlin safe; do not move the AHU or the chain block.
- First aid and ambulance; inform site management and the client's representative.
- Preserve the scene: photograph the hook, purlin, sling and load; quarantine the chain block and lifting gear; retain the sketch lift plan and the expired certificate; identify witnesses.
- Notify the Labour Department (Occupational Safety and Health Branch) and the police; failure of a load-bearing part of a lifting appliance is a notifiable dangerous occurrence under the Factories and Industrial Undertakings Ordinance.
- Report under the Employees' Compensation Ordinance: Form 2 within 14 days for a non-fatal accident causing incapacity; a fatality must be reported immediately.
- Notify the insurer and the client, open the incident file, and brief the workforce factually without prejudging blame.
Then: a competent person inspects the purlin and the gear; the gear stays out of service until re-examined; a structural check of the purlin is commissioned; the safety officer's earlier minute is preserved as evidence. The investigation must run in parallel with recovery, not after it.
2. Carry out a causal analysis. Explain why the supervisor's explanation is not a root cause.
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Direct cause. The top hook was hooked over the purlin flange without a shackle or positive attachment and slipped off when the load was slewed.
Contributing conditions. No engineered lifting point; no structural check of the purlin; no exclusion zone; workers under the load; signalman doubling as banksman; expired periodic examination certificate; no approved lift plan or permit-to-lift.
Root (organisational) causes. No process for reviewing and approving lift plans; lifting-gear certification not tracked; production pressure; the safety officer's warning was not actioned; supervision and competence gaps; a culture in which a hand sketch was accepted as a plan.
Why the supervisor's explanation fails. Saying the workers should have known explains nothing about why the system permitted an unapproved lift, with expired gear, no exclusion zone and a hook with no positive attachment. It stops the investigation at the injured person and guarantees repetition. Under the hierarchy of controls the reliable fixes are engineered - certified lifting points, shackles, physical barriers - and procedural, not exhortation. The supervisor's own conduct is a separate disciplinary question; it is not the cause of the accident.
3. Recommend corrective actions with a hierarchy of controls and explain how you would verify that they work.
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Corrective actions, strongest first
- Eliminate or reduce: pre-assemble as much as possible on the roof; use a mobile crane or a certified monorail instead of a purlin.
- Engineering: designed and certified lifting points, shackles and anti-slip attachments, spreader beams, physical barriers around the drop zone, tag lines so nobody steadies a load by hand.
- Administrative: lift plan and permit-to-lift for every lift above a defined threshold, approved by a competent person; a lifting-gear register with expiry dates and a hold on use when expired; dedicated banksman and signalman; toolbox talks; stop-work authority.
- PPE: last line, never the plan.
Verification. Re-examine and re-certify all gear; audit the register monthly; observe the next three significant lifts; check the permit process is actually used rather than completed retrospectively; review the safety officer's raised items weekly with named owners and close-out dates. Report findings and actions to the client and the safety committee, and track recurrence. Adopt a just-culture response: the process failure is management's, and the lesson belongs in the lift-planning system, not only in a disciplinary file.