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CROSS Safety Report

Mobile scaffold tower falls 7 storeys

Report ID: 436 Published: 1 April 2014 Region: CROSS-UK

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Overview

A mobile tower, which was not being used, toppled over the guardrail and fell 7 storeys (27m) to the ground.

Key Learning Outcomes

For construction professionals:

  • Mobile towers should have wheels locked and be properly secured to the structure when not in use

  • Towers should be securely stored/dismantled if wind speeds exceed the stated limits. Wind tolerances of each tower should be checked with manufacturers.

  • This advice should be included within the risk assessment and method statement (RAMS) and highlighted to the work crew

  • Wind speed measuring equipment can be used when high winds are predicted and to develop a Site Action Plan to mitigate the adverse effects

  • Consider restricting the use of mobile towers on high rise/exposed sites and use MEWP’s as an alternative, where practicable

Full Report

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A report has been received about a potentially high impact event on a city centre site during very high winds. Despite numerous controls to prevent falling objects, a mobile tower, which was not being used, was blown across the floor plate and hit the edge protection.

Such was its momentum that the tower toppled over the guardrail and fell 7 storeys (27m) to the ground (Figure 1).

Image
Figure 1: scaffold debris on footpath

This, says the reporter, clearly had the potential to cause fatalities and serious injuries. Lessons to be learned are:

  • Mobile towers to have wheels locked and be properly secured to the structure when not in use

  • Wind tolerances of each tower to be checked with manufacturers

  • Towers should not be used but be securely stored/dismantled if wind speed exceed the stated limits. The advice should be included within RAMS / TCS.

  • High rise/exposed sites to utilise wind speed measuring equipment when high winds are predicted and to develop a Site Action Plan to mitigate the adverse effects when identified triggers are reached

  • High rise/exposed sites to restrict use of mobile towers on high levels, consider MEWP’s as an alternative, where practicable

Expert Panel Comments

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Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.

The incident is a dramatic illustration of the generic risk of falling objects. Readers should note that anything falling from height has the potential for serious consequences and indeed one of the greatest hazards in the urban environment during wind storms is the damage caused by flying debris.

Loose material on roof tops is particularly hazardous and a member of the CROSS Panel has seen unsecured scaffold boards be lifted and fly over a 2.5m high sheeted scaffold and down 25 storeys in gusty conditions.

It is important to realise the potential force of the wind and the local forces that can act. What provisions are made for wind storms during construction? All it takes is one incident in the centre of a major city resulting in a death that will see a sea change in the procedures in use.

There has been considerable work by Professor Brian Lee at Portsmouth University who has developed design rules for take-off speeds for different shaped projectiles. For example, refer to: A Model of Wind–borne Debris Damage.

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