Mobile scaffold tower safety: the rules and the checks

What does EN 1004-1:2020 set for a tower?

EN 1004-1 is the product standard for mobile access and working towers made of prefabricated parts. It replaced EN 1004:2004, which was withdrawn on 30 November 2021, a year after the new edition was published (PASMA EN 1004 guide). The scope covers towers up to 12 m indoors and up to 8 m outdoors (NS-EN 1004-1 abstract). The changes that matter most to users:

The load classes are class 2 at 1.5 kN/m² (about 150 kg per square metre) and class 3 at 2.0 kN/m² (about 200 kg); there is no class 1 for towers, and the load has to be spread over the platform rather than stacked in one spot. The designation also names the access type with four letters: A for a stairway, B for a stair ladder, C for an inclined ladder and D for a vertical ladder, with X where a type is not offered. Standards are not retrospective, so a sound tower made to the 2004 edition may still be used; check whether its maker has issued a newer manual. For the platform loads behind these classes, see our article on scaffold load classes.

Stabilisers, outriggers or ballast: what does a tower need?

Whatever the schedule of components in the manual says for that height and that position. The PASMA Operator’s Code of Practice (2019, revision 13) is blunt about the old shortcuts: the stability of a tower comes from calculations in the product standard, and it is "not appropriate or sufficient" to work out the maximum platform height from a base-to-height ratio (PASMA Code of Practice). The practical rules from the code:

• Fit stabilisers or outriggers at the first opportunity, usually as soon as the base level is complete, and widen them as the tower grows if the manual says so.
• Stabilisers suit towers that stay put; outriggers, which carry their own adjustable legs and castors, are the better choice for a tower that is moved often.
• When a tower stands against a wall and the stabilisers are moved, the wall has to be at least two thirds of the tower’s height to stop it overturning. Where a tower is tied to a building, the anchors follow the same rules as any scaffold tie; see scaffold ties and anchoring.
• Where stabilisers, outriggers or ties cannot give stability, ballast may, but only as specified in the manual, made of solid material (not sand or water) and fixed to the tower.
• Adjustable legs are for levelling only. One leg should stay at minimum extension, and you never wind them out to gain height (PASMA safety FAQ).

Side loads tip towers as surely as wind. The code puts the allowable side load at the platform at generally 20 kg, and gives an example: a pressure washer using 10 litres a minute at 140 bar pushes back with about 28 kg at 30 cm from the surface. Drilling into a wall or leaning a ladder against the tower has the same effect. You can see how a manufacturer’s table changes the base set-up from height to height on our mobile scaffold tower pages.

When is it too windy to use a tower?

PASMA’s line is clear: if the average wind reaches Beaufort force 4, 17 mph (27 km/h, 7.6 m/s), stop work and dismantle the tower. It recommends checking the forecast as part of the risk assessment and carrying a hand-held anemometer on site. Two situations make wind worse. Sheets, banners or cladding panels act like sails and can overturn a tower in light winds, so such a tower has to be tied in at all times, with the supplier’s advice. Open-ended buildings, such as hangars and unclad frames, can funnel wind harder than in the open.

Manufacturers do not all draw the line in the same place. A Layher Uni Standard manual, for example, tells users to move the tower to a sheltered spot or secure it against overturning when the wind exceeds force 6 or at the end of a shift (Layher Uni Standard instructions). Where the manual and the PASMA code differ, settle it in the risk assessment; the lower figure is the cautious one.

3T or AGR: how do you build without standing on an open platform?

PASMA, together with the health and safety authorities, recommends two methods for assembly, alteration and dismantling (PASMA: 3T and AGR):

• 3T (Through the Trap). The erector sits in the trapdoor of the platform and fits the guardrails and horizontal braces for the level above, so collective protection is in place before standing up.
• AGR (Advance Guardrail). Separate guardrail units are locked in place from the level below and then raised. On many towers the AGR frames are part of the structure as well as the edge protection, so they must not be removed while the tower stands.

Either way, follow the frame sequence in the manual every time, because it changes with height. A facade scaffold is built differently, lift by lift with ties to the wall; see how to erect scaffolding. Do not clip a harness lanyard to a tower: an arrested fall is likely to pull it over. Examples: the BoSS Clima 3T and the BoSS Clima AGR.

How do you move a tower?

Under the PASMA code, a tower is moved only by or under a competent person, after checking the route for holes, ducts, gratings and overhead cables. Nobody and nothing stays on it. Reduce it to a platform height of 4.0 m, leave the stabilisers fitted but raised no more than 25 mm (1 in), push at or near the base and never pull it towards you. Never move a tower with a forklift or a vehicle. Afterwards, lock the castors, check that the tower is complete, and level it with a spirit level.

What does OSHA require for mobile (rolling) scaffolds in the US?

29 CFR 1926.452(w) covers mobile scaffolds, often called rolling scaffolds in the US (eCFR text via Cornell LII):

• Brace the scaffold against racking and keep it plumb, level and square; lock casters and wheels with positive locks while it is in use.
• Apply manual force no more than 5 ft (1.5 m) above the supporting surface, and never use a truck, forklift or add-on motor unless the scaffold is designed for it.
• Employees may ride a moving scaffold only if the surface is within 3 degrees of level, the height is no more than twice the base width (unless it passes a recognised stability test), outriggers are fitted on both sides, power propulsion does not exceed 1 ft per second, and nobody stands beyond the wheels.
• Level with screw jacks, pin the caster stems, and tell everyone on the scaffold before it is moved.

The general rules in 1926.451 also apply: fall protection above 10 ft (3.1 m), a top rail between 38 and 45 inches on scaffolds placed in service after 1 January 2000, inspection by a competent person before each work shift, and erection, moving and dismantling only under a competent person’s supervision (29 CFR 1926.451).

How often must a tower be inspected in the UK?

For towers where a fall of 2 m or more is possible, PASMA’s best practice is to inspect after assembly or significant alteration and before use, write the report before going off duty, hand it over within 24 hours, and re-inspect at least every 7 days and after anything that may have affected stability, such as bad weather. Moving the tower around the same location does not need a new report. On a construction site, keep the report until the work is finished and then for three months at the office. Our scaffold inspection checklist lists what to look at.

ScaFix’s tower pages list the parts, stabilisers and ballast for each platform height as the manufacturer’s tables give them, so you can check a set-up before it goes on the van.

This page is planning information, not structural approval. The tower’s instruction manual, the Work at Height Regulations and HSE guidance in the UK, and 29 CFR 1926 Subpart L in the US decide what may be built and used; a competent person must inspect the tower.

Frequently asked questions

Sources

Primary sources used for this article, with the date each was read.

• PASMA Operator’s Code of Practice (2019, revision 13) (read 23 October 2026)
• PASMA: EN 1004 complete guide (read 23 October 2026)
• PASMA: safety FAQs (read 23 October 2026)
• PASMA: 3T and AGR (Advance Guardrail) (read 23 October 2026)
• Standard Norge: NS-EN 1004-1:2020 abstract (read 23 October 2026)
• 29 CFR 1926.452 Additional requirements for specific scaffolds (Cornell LII) (read 23 October 2026)
• 29 CFR 1926.451 General requirements (Cornell LII) (read 23 October 2026)
• Layher: Aufbau- und Verwendungsanleitung Fahrgerüst Uni Standard (hosted by Niklaus Baugeräte) (read 23 October 2026)