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436 Mobile scaffold tower falls 7 storeys

Report ID: 436

Published: Newsletter No 34 - April 2014

Report Overview

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

Report Content

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.

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.

Comments

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”. J.A.B. Wills, B.E. Lee, T.A. Wyatt, Journal of Wind Engineering and Industrial Aerodynamics. Vol 90. pp 555-565, July 2002.

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