5.2 Scaffold Design, Loading, Competent Scaffolders and Safe Erection & Dismantling

When does a scaffold need engineering design?

Current law. CDM 2024 regulation 21(2) requires any support, temporary support or temporary structure to be designed, installed and maintained to withstand any foreseeable load, and used for the purpose for which it was designed. Regulation 21(3) adds that no structure may be loaded until it becomes unsafe. Every scaffold therefore needs a design basis:

• Standard configurations: a proprietary system used within the manufacturer's published configurations, or a tube-and-fitting scaffold built to a recognised standard design. The design is the manufacturer's or standard's tables, applied by a competent scaffolder.
• Non-standard scaffolds: for example cantilevered, suspended, very tall, heavily loaded, sheeted in exposed locations, supporting hoists or loading bays, or on unusual foundations. These need a bespoke design by a competent engineer, with drawings and calculations kept on site.

DOSH's falls guideline (section 5.6) calls scaffolds not built to an accepted international standard special scaffolds. Expert advice from a professional engineer should be obtained before they are built and used, and every user must be told their maximum safe live load. DOSH's work-at-height page adds that equipment such as scaffolding "must be installed according to the approved design and manufacturer's instructions".

What the repealed BOWEC rule said. BOWEC regulation 75(1) required every metal tube scaffold exceeding 40 m in height, and every other scaffold exceeding 15 m, to be built to the design and drawings of a Professional Engineer. Other metal tube scaffolds needed design approval from the Chief Inspector, and DOSH's 2016 guideline on scaffold design approval set out that process. Regulation 75 was repealed with BOWEC on 1 June 2024. The 15 m and 40 m figures are still sensible points at which to involve an engineer, and many clients and specifications continue to use them, but cite them as former law.

Loading: platform load classes

Overloading is a common cause of scaffold collapse. Platforms are designed for a uniformly distributed load (UDL) class. The European scaffold standard EN 12811-1, widely used for system scaffolds, defines six service load classes:

Rules the SSS enforces:

• Show the load class or safe working load on the scaffold tag and tell users (DOSH 5.6).
• Do not land a full pallet of blocks on boards. Concentrated loads go on loading bays designed for them, over transoms and close to standards.
• Do not allow more loaded lifts or bays than the design permits.
• Treat sheeting, netting, banners and hoists as design changes, because they add wind and point loads.

Competent scaffolders

CDM 2024 regulations 10 and 17 require contractors to use people with the necessary skills, knowledge, training and experience. DOSH's falls guideline says a damaged scaffold must not be used until it has been referred to a certificated scaffolder for repair.

DOSH runs a competent person registration for scaffolders (pengendali perancah). Its application form (DS-07-003) offers three competency classes: basic (asas), intermediate (pertengahan) and advanced (tertinggi), with renewal before the competency expiry date. Training is delivered by DOSH-registered scaffolder training centres under DOSH's 2016 guideline. On site:

• check that the scaffolding contractor's erectors hold valid registrations suited to the scaffold type
• make sure a competent person supervises erection, alteration and dismantling
• forbid other trades from altering scaffolds; put this in the site rules

Safe erection

Before starting

• Approved design or manufacturer's instructions on site
• Ground prepared: compacted, drained and level
• Exclusion zone with barriers and signs below; gantry or fan where the public or other workers pass
• Overhead power lines identified and managed (CDM regulation 27)
• Weather forecast checked; materials inspected, with damaged tubes, fittings and boards rejected
• Method statement and HIRARC briefed to the gang

Fall protection for erectors

• Use advance guardrail systems where the scaffold type allows, so a guardrail is in place before the erector steps onto a new lift.
• Otherwise use harnesses with lanyards anchored to suitable scaffold members above the harness attachment point, so the fall factor stays at 1 or below (DOSH section 8). Twin lanyards keep the erector attached while moving past obstructions.
• Board each lift fully as erection progresses, rather than working from single boards.

Handling materials

• Never throw or drop tubes, boards or fittings. Use a gin wheel with a suitable rope and safety hook, a hoist, or a crane with taglines.
• Keep platforms clear of loose fittings and store materials on designed bays.

Ties and bracing

• Fit ties and bracing as erection proceeds, at the designed spacing.
• Never leave a lift standing above the last tie further than the design allows.

Handover

When the scaffold is complete, a competent person inspects it before first use, records the inspection and displays the status tag (Section 5.3).

Alterations

Alterations, such as removing a transom for a hoist or moving a tie for a window frame, are a leading cause of scaffold failure. Controls:

1. Alterations only by the scaffolding contractor's competent scaffolders, with the supervisor's approval.
2. Take the affected area out of use (red tag) during the work.
3. Get engineering approval where the alteration departs from the design, for example removing ties, adding sheeting or creating a loading bay.
4. Re-inspect and re-tag before reuse.

Dismantling

Dismantle broadly in the reverse order of erection, from the top down, lift by lift:

• Set an exclusion zone first. Lower materials in a controlled way and never drop them.
• Never remove ties ahead of the dismantling. Ties stay until the scaffold above them has been dismantled to that level, and bracing is kept until its lift comes down. Removing ties early leaves a tall, unbraced structure that can overturn in wind or under its own weight.
• Keep guardrails on the working lift as long as possible, and use fall arrest when they are removed.
• Do not leave a partly dismantled scaffold overnight in an unstable or accessible condition. Tag it red and barricade it.

Scenario: the 46-metre façade scaffold

A subcontractor plans to extend a standard tube-and-fitting scaffold from 38 m to 46 m. Masons have already landed two 1.3-tonne pallets of bricks on a light-duty (load class 2) lift. The SSS:

1. Stops the extension. The scaffold is outside its standard configuration, the extra height increases loads on the lower standards and the wind loading, and the design must be checked by a competent engineer under CDM regulation 21. The former BOWEC regulation 75 would also have required PE design above 40 m.
2. Clears the overloaded lift at once and tags it red. The pallets are removed by crane and the platform is checked for damage.
3. Arranges an engineered loading bay for masonry materials and updates the scaffold tags to show the load class of each part.
4. Briefs all trades that only the scaffolding contractor may alter the scaffold, and records the event as a near miss.