Erection Sequence for a Birdcage Scaffold in an Occupied Atrium
A birdcage scaffold is to be erected inside a five-storey atrium of an occupied shopping centre to allow replacement of ceiling glazing panels. The atrium floor is polished stone with a 300 mm raised access floor over a service void. The birdcage will be 8 m × 6 m in plan and 15 m high, with standards at 1.8 m centres. The centre is open to the public 09:00–21:00, and the works must proceed without closing the atrium. The contractor proposes to erect the birdcage from the ground up, using a mobile tower as a temporary access platform, and to load materials onto the birdcage decks as it rises. The centre's fire officer is concerned about the escape route that passes within 2 m of the proposed scaffold footprint.
1. Assess the proposed erection sequence and identify the sequencing and access problems. What sequence would you require?
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Problems with the proposal:
- Loading as it rises: Loading decks progressively means the structure is partially loaded before it is complete and tied. The design may assume full continuity; partial loading can overstress individual standards. Materials should be landed at a designed location, not distributed ad hoc.
- Mobile tower access: A mobile tower alongside a 15 m birdcage in a public atrium is a fall and falling-object risk. The tower must be within the birdcage footprint or a designed access stair should be built into the birdcage.
- Public interface: Erecting from the ground up in an occupied atrium means members are lifted over the public. A exclusion zone and a planned lift sequence are needed.
- Raised access floor: The 300 mm raised floor over a service void cannot be assumed to carry the scaffold leg loads without a designed spreader arrangement. The service void must be surveyed and the floor checked.
Required sequence:
- Survey and protect the raised floor; install designed spreader plates over the void, or found the standards on the structural slab.
- Erect the first lift, deck it, and install guardrails before progressing.
- Build in a designed internal access stair rather than relying on a mobile tower.
- Erect in a planned sequence, tying/braciing as designed, and land materials only at designated points.
- Maintain a public exclusion zone and a banksman throughout.
2. The fire officer's concern is the escape route within 2 m of the footprint. How would you resolve this, and what does it mean for the method statement and the handover?
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Resolution: The escape route must remain available at all times. Options, in order of preference:
- Re-site or reduce the footprint so the escape route retains its designed width and is not obstructed.
- Provide a protected alternative route of equivalent width and signage, agreed with the fire officer and the centre's responsible person, before erection starts.
- Phase the works so the route is only affected briefly, with a documented temporary arrangement.
A 2 m clearance to a scaffold is not automatically acceptable: falling objects, dust and the scaffold's own stability (if struck) are all relevant. The route must not pass under or through the scaffold.
Method statement: Must include the escape route arrangement, signage, the exclusion zone, the phasing, and the name of the person responsible for maintaining the route. It must be agreed with the fire officer and the centre's responsible person before work starts.
Handover: The handover certificate and tag must record the escape route arrangement and any conditions (e.g. 'route to remain clear at all times; no storage'). The inspection regime must include checking the route is clear. Any change to the route is a design change requiring re-approval.