Dismantling Over a Live Entrance
A 12 m high independent scaffold wraps a three-storey office refurbishment. The ground floor entrance must stay open for tenants, and a covered walkway protects pedestrians. The scaffold is to be struck over four days. The site manager plans to start at the bottom, removing the lowest lift boards first so the upper lifts are lighter, and to lower boards by hand to two labourers below. The weather forecast includes gusts of 50 km/h on day two. Ties are to be removed as the work descends, and the last two lifts will be taken down without a tie because 'they are only small'.
1. Identify the errors in the proposed dismantling sequence and explain the correct principle.
Read the worked answer
The plan is reversed. Dismantling proceeds from the top down, lift by lift, so that the structure is never left with unsupported upper sections. Removing the bottom lift first undermines the standards and braces that support everything above. Ties must not be removed ahead of the work; they are removed only as the dismantling reaches them, keeping the remaining scaffold tied and stable. Leaving the last two lifts untied is unsafe because even a short unbraced section can be blown or pulled over, and the top is where wind leverage is greatest. Boards and components should be lowered in a controlled way, not dropped or hand-passed to people standing underneath, and the area below must be excluded.
2. State the controls needed for the entrance, the weather, and the final untied section.
Read the worked answer
Entrance and pedestrians: maintain the protected walkway, add a exclusion zone under the work face, and schedule noisy or falling-object risk periods. Use a gin wheel, rope and controlled lowering, or a hoist, with a competent banksman; never drop boards. Weather: set a wind limit agreed with the scaffold designer, stop work and secure or partially dismantle loose components before gusts reach the limit, and inspect after strong winds. Final section: plan the sequence so the last lifts are removed while still tied where possible, or provide temporary stability such as guys or props agreed by a competent person; never leave an untied lift standing overnight. A competent person should supervise the strike and inspect at each stage.