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Case Study

Silica in Construction: Changes to approved methods of roof tile cutting

The Client

HSE and industry stakeholders from the house building sector.

The Problem

When cutting roof tiles, workers are exposed to respirable crystalline silica (RCS).  This dust, if breathed in, causes severe lung diseases such as silicosis. HSE have produced a video of the effects of silicosis on people's lives.

Impact of silicosis (video)

Valley tiles are created where rooves meet (see picture). These tiles need to be trimmed to fit. An interim agreement between industry and HSE allowed valley tiles to be cut using hand held power tools without wet dust suppression systems, which would introduce additional safety hazards, such as slips.

A house with a sloping roof has a room with a window in the roof space. The window extension also has a sloping roof, built out at 90 degrees to the main roof. Where the two rooves meet is called the 'valley'. There the rectangular tiles of the extension had to be cut across at an angle in order to join flush with the sloping main roof.

What We Did

In order to properly assess the health risk associated with this HSL measured RCS exposures during the cutting of valley tiles.

Cutting tiles along one valley edge took less than 10 minutes and only occurred once or twice per day. Because of this short exposure period we used innovative high volume respirable dust samplers to measure RCS exposures, which would not have been possible using conventional sampling techniques. We also used our exposure visualisation techniques (ELVIZ) system to record both real time exposure and video of the process.


The exposure monitoring showed that if a worker cut two roof edges of valley tiles in a shift, equating to about fifteen minutes of work, then they would have already reached or exceeded the 8 hour time weighted average RCS exposure limit. We also demonstrated that adjacent workers were at significant risk and that the use of other exposure controls, such as dust masks, could be improved.

Changes to working practice

Our findings led to a change in working practices in the construction sector. Valley tiles are now marked up at roof level and taken to a fixed location where they are cut whilst using engineering controls such as water suppression.

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