Removing a Raking Tube to Pass a Window Unit
On a 7/F truss-out scaffold at a hotel in Tsim Sha Tsui, the scaffold has been inspected and tagged 'safe for use'. The platform is 1.5 m wide and supported by two raking tubes and four anchor bolts. The hotel engineer asks the scaffolder to remove the lower diagonal raking tube so a replacement window unit can pass through, and to add a 1.2 m extension to the platform so a worker can reach a ledge. The scaffolder is told the work will take 'ten minutes' and the tag can be changed afterwards. Two workers are already on the platform. The original designer is not on site.
1. Why is removing the lower diagonal raking tube and adding a 1.2 m extension not a 'ten-minute' alteration?
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The raking tube is part of the stability system: it carries shear and overturning loads back to the anchors and helps brace the truss-out frame. Removing it changes the load path and can increase the tension and shear on the remaining anchors, couplers and tubes. The 1.2 m extension also changes the geometry: it adds dead load, moves live load further from the supports, increases eccentricity and creates additional wind and working loads. The original design and the existing tag no longer apply. This is a structural alteration, not a convenience adjustment, and 'ten minutes' ignores the need for redesign, temporary support and re-inspection.
2. Set out the correct procedure, including who authorises the work and the sequence.
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Work should stop and the platform should be cleared. The request should go to the contractor and the original designer or another competent engineer, who must confirm whether the raking tube can be removed and whether the extension is structurally acceptable. If approved, a revised design and method statement are needed, including temporary support before the raking tube is released, additional ties or anchors if required, and a safe sequence for installing the extension.
The alteration should be carried out by trained scaffolders under supervision, not by workers on the platform improvising. After alteration, the competent person must inspect the scaffold before it is used, and a new tag issued. If the designer does not approve, an alternative route for the window unit or a different access method must be used. The hotel engineer can request the change, but cannot authorise the structural alteration.
3. What records and tag changes are needed before the platform is used again?
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The old tag must be removed when the alteration starts, because the scaffold is no longer in its inspected condition. Records should include the alteration request, the revised design or engineer's approval, the method statement, the temporary support check, the post-alteration inspection record and the new tag with date, time and inspector's name. Workers should be briefed on the changed configuration and any new load limits. The building management should be informed of the work and any change to public protection. Without these records, a new tag would only hide an uncontrolled change.