Excuse my dust

The threat posed by silica dust to construction workers is as old as masonry itself. But although it is known to be harmful to health, this risk has been largely hidden in the shadow of more virulent and alarming health hazards – asbestos being the obvious example.  Many health & safety professionals believe the seriousness of silica dust has been underplayed for too long. Some have even said it is only a matter of time before silica dust becomes the next big issue in the construction workplace. 

The Health and Safety Executive has been pushing the industry to adopt solutions for many years and in some instances the advice has been taken on board. Most construction equipment manufacturers have responded to the calls and developed dust-capture systems for construction tools.  But this response has been patchy and the uptake disappointing on site. On many construction sites, particularly smaller ones,  dust is still not viewed with the same fear and respect afforded to asbestos. In short, for a long time no one seemed interested.  In recent years the dangers of silica dust exposure have become better understood and there has been an increase in interest from the industry.

Over the past three years measurement equipment suppliers have reported an increased interest in their products from contractors – something that was not present in earlier years. However there is still some way to go. Construction workers as well as health and safety professionals need to be aware of the dangers and know what steps to take to mitigate them.  Concrete, brick, stone and similar materials can contain between 20% and 70% crystalline silica. Construction processes involving such materials can release respirable crystalline silica (RCS) dust into the air – sharp crystalline particles which can damage tissue in the gas-exchange region of the lungs causing scar tissue to develop.  Exposure can lead to a number of serious health problems including silicosis, chronic obstructive pulmonary disease (COPD), bronchitis, emphysema and lung cancer.  The construction industry is the largest volume consumer of silica-containing materials and anyone working with these materials is likely to be exposed to RCS to some extent. A recent review of literature by the Health & Safety Laboratory suggests there are roughly half a million construction workers with the potential for silica dust exposure.

The same review suggests that silica dust exposure leading to lung cancer is responsible for over 800 deaths a ear.  As a hazardous substance RCS is covered by the Control of Substances Hazardous to Health Regulations 2002 (COSHH). The daily Workplace Exposure Limit (WEL) for RCS is currently 0.1mg of dust per cubic metre of air.  This is a very small amount – a pile of dust smaller than your thumbnail.  Even this tiny amount is not safe. The exact link between dust exposure and the instance of health effects is complicated and the subject of ongoing research, but essentially more exposure means more risk; so exposures should be as low as practically possible.  To mitigate the risks posed by silica dust, construction firms first need to understand the different factors that impact upon exposure levels.  Duration of exposure has a big effect. Where a worker is positioned while using a tool also affects exposure, for example a user standing in the dust plume from a diamond blade chasing into concrete will be exposed to high levels of RCS.  The working environment can also play a major role in determining the level of silicadust exposure experienced by workers.  Working in enclosed areas can significantly increase exposure while working in the open will often lead to lower exposure levels (although that does not mean the dust will not pose any health risks or be a nuisance to the worker).

In terms of the task, any abrasive work involving concrete, stone or masonry will cause silica dust to become airborne.  If it is possible to carry out works without creating excess dust, then that should be the first option. When this is not possible contractors need to have systems in place to protect their workers against the threat of high levels of RCS dust exposure.  If a ‘dusty’ task is necessary the first line of defence is control at source.  Water suppression is very effective for tools and processes that will not be affected by moisture and is a common method used on site. But this is not a silver bullet and there are a number of disadvantages with water suppression, such as the creation of a water and dust slurry (a particular problem on high-rise projects where the slurry can be tricky to constrain), and the requirement of a constant supply of water to the suppression equipment. On-tool extraction can also be effective.  The dust is captured by a vacuum hood attached to the tool or the substrate. Site vacs and dust extractors are rated L (low), M (medium) or H (high). The European Power Tools Association has suggested that an M-rated vac is the minimum acceptable for use with RCS dust, and recommends the higher protection afforded by an H-rated vac – a conclusion corroborated by HSE research.

At our laboratory at VJ Technology we have tested many different dust hoods, some of which work well. However there are a number of sub-standard products on the market which experience significant issues including poor clamping to the machine, clogging up, wearing out, or simply being too flimsy for use on a construction site.

Area ventilation is useful for limiting the concentration of dust especially where work is entirely enclosed, for example in tunnelling projects or with ‘live’ refurbishment work, where the rest of the building is still in use. This approach should be employed in conjunction with the use of on-tool extraction to ensure minimum exposure to RCS dust.  Respiratory protection equipment (RPE) is the last line of defence against dust exposure.  Every effort must be made to capture the dust at source but RPE can still prove invaluable in dealing with any residual dust that might escape. Even if the dust capture or suppression is effective a dust mask with an “Assigned Protection Factor” of at least 20 (FFP3 or P3) would be advisable.  Dust mask selection is a big topic and there is guidance available from suppliers, manufacturers and the HSE on choosing RPE.  One key issue is that once a suitable mask is identified, it must be fit tested. The Fit2Fit website (www.fit2fit.org) provides guidance on fit testing and fit test providers.  The construction industry has made some good progress over the past few years.  Awareness is increasing and dust control measures are now in place on many sites.  Water suppression is widely used and the demand for M- and H-rated vacs, fit testing and other dust control equipment has seen a marked increase recently. However a lot of equipment in use on sites is still not up to the job – either because the equipment itself is not of a good enough quality or because it is being deployed in a way that increases the exposure of the user to dust.  We have made progress but the diverse nature of construction work and its workforce means that a coherent solution to dust control within the industry remains a challenge 

About the author: Dr Tom Gunston is test laboratory manager with VJ Technology, a leading supplier of fixings, anchors, consumables and power tools to the construction industry

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