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575 Scaffold overturn

Report ID: 575

Published: Newsletter No 45 - January 2017

Report Overview

A 5m high scaffold screened with fabric overturned when airflow was introduced to a building.

Report Content

This concerns a 5m high scaffold screened with fabric that was erected to protect against debris and dust from adjacent demolition works of the arched structures below a building. When the demolition broke through into the arched structure, airflow was introduced producing horizontal load on the scaffold which overturned. It fell onto a section of a pedestrian route for the site team and fortunately there were no injuries.

The root cause of the event, says the reporter, was misinterpretation of the scaffold standard TG20:13 Good Practice Guidance for Tube and Fitting Scaffolding in that the need for a designed scaffold was not appreciated, wind loading was not considered, and there were inadequate ties to the masonry arch. A procedure was in place that stated all classes of temporary works/scaffold should be on a register which this was not, and whilst the scaffold requirement was discussed on site at a temporary works planning meeting, this did not cover the scaffold screens.

Comments

All internal structures can be subjected to horizontal loads, including wind pressures, and should be designed as such.

This is almost a classic case of not considering the safety attribute of ‘sensitivity’. The original assumption of no wind was wrong so even a slight pressure would have been serious.

Achieving robustness always requires a presumption of some horizontal forces but there is always also danger in assuming low wind speeds for temporary works designs. The force difference in say going from 2m/sec to 4m/sec is (4/2)2 = an increase of 400%.

It is essential that temporary works are designed and constructed to BS5975 and associated TWf guidance, with any fixings needed for stability designed and constructed to BS8539 and CFA guidance.

Images

Overturned scaffold



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