Skip to main content

CROSS Safety Report

Spalled concrete falls from rear face of drilled hole 26 floors up

Report ID: 639 Published: 1 July 2017 Region: CROSS-UK

This report is over 2 years old

Please be aware that it might contain information that is no longer up to date. We keep all reports available for historic reference and as learning aids.

Overview

A reporter describes how during drilling, an operator over drilled the hole causing spalling on the back face of the concrete.

This caused a lump of concrete to fall down the shaft where operatives were working.

Key Learning Outcomes

For construction professionals:

  • It is good practice to carry out risk assessments for all construction activities. This can help to ensure all risks are identified and the appropriate measures implemented.

For civil and structural design engineers:

  • When specifying post-installed anchors, the hole depth should be specified as well as the embedment depth to ensure the operative is clear on how deep they must drill

  • Be aware that the depth of hole required can vary between manufacturers

  • Where the back face of drilled holes is exposed to a fall, attention should be brought to contractors to review provisions for closing off or protecting areas which may be exposed to falling debris during drilling

Full Report

Find out more about the Full Report

Our secure and confidential safety reporting system gives professionals the opportunity to share their experiences to help others. If you would like to know more, please visit the reporting to CROSS-UK page.

Holes were being drilled for resin-anchor fixings, where the back face of the wall being drilled was located above a 26 storey lift shaft. The holes were specified as 150mm deep, within a 250mm thick wall, to suit M20 resin-anchored fixings.

During drilling, it appears that the operator over-drilled the hole (drilling deeper than the 150mm hole depth specified) and this caused spalling on the back face of the concrete, causing a lump of concrete to fall down the shaft. The lump of concrete was approximately 80x40x35mm. There were people working in the shaft at the time, however thankfully no-one was hurt. A number of learning points can be made:

  • The manufacturer's requirements for the minimum thickness of the base material are important, as these define the required thickness of concrete left beyond the end of the hole (typically 2x the hole diameter). Exceeding this drill depth carries a risk of debris spalling off the back face.

  • The hole depth should be specified as well as the embedment depth to ensure the operative is clear on how deep they must drill. This varies between manufacturers.

  • Where the back face of drilled holes is exposed to a fall, attention should be brought to contractors to review provisions for closing off or protecting areas which may be exposed to falling debris during drilling

The hole depth should be specified as well as the embedment depth to ensure the operative is clear on how deep they must drill. This varies between manufacturers

Expert Panel Comments

Find out more about the Expert Panels

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.

This is a useful report with important lessons to be learned as it highlights a risk which is not commonly thought about. Falling objects on site (tools or materials) are a generic hazard but the creation of debris by excess drilling is not a problem regularly reported. It also illustrates the need to undertake adequate risk assessment when undertaking designers’ duties, so that hazards can be adequately communicated to site on drawings.

Share your knowledge

Your report will make a difference. It will help to create positive change and improve safety.

Our secure and confidential safety reporting system gives professionals the opportunity to share their experiences to help others.