Airborne hazardous substances – Trailing in the dust

Many professionals in the construction industry are waking up to the risks posed by airborne dust particles, but there’s no doubt that awareness of the issue among some remains worryingly limited. Tom Gunston considers the health effects brought about by silica-dust exposure and explores the potential control measures.
An understanding of the dangers posed by respirable silica dust and the steps that can be taken to reduce risks in the workplace are essential to overcome what could be the next big challenge for construction health and safety professionals. The notion that silica dust can cause serious health problems has taken some time to filter through to the construction industry. Some construction-equipment manufacturers were informed about the risks and developed dustless attachments for tools, but they didn’t sell. In short, no one seemed interested. The HSE has been highlighting dust as an issue for many years. In some instances, its advice was embraced by the industry. Petrol cut-off saws, for example, were recognised as posing an issue, but one that could be solved through water suppression. However, until recently, some of the broader issues surrounding control of silica-dust exposure in construction remained far from the forefront of the industry’s thinking.
The dangers of dust
Hazardous dust can be loosely divided into ‘inhalable’ and ‘respirable’ dust. Inhalable dust consists of larger particles, which are usually visible to the naked eye and can enter the mouth, nose and upper parts of the lungs. Respirable dust consists of finer particles. Invisible to the naked eye, these can travel into the deepest part of the lungs, known as the gas-exchange region, where oxygen is absorbed into the blood and carbon dioxide is released from the body back into the air. Concrete, brick, stone and similar materials can contain between 20 and 70-per-cent crystalline silica.2 Any ‘dusty’ process using these materials releases fine silica dust particles into the air. Respirable crystalline silica (RCS) dust consists of tiny but very sharp crystalline dust particles. If breathed in, these particles can damage tissue in the gas-exchange region, causing scar tissue to develop. Exposure can lead to a number of serious health problems, including silicosis, chronic obstructive pulmonary disease (COPD) – which includes bronchitis and emphysema – and lung cancer.
Exposure limits
As a hazardous substance, RCS is covered by the Control of Substances Hazardous to Health Regulations 2002 (COSHH). The daily exposure limit for RCS is given as a Workplace Exposure Limit (WEL). The current daily limit value is 0.1 milligrams of RCS dust per cubic metre of air. This is a very small amount – illustrated in the HSE ‘Time to Clear the Air’ leaflet5 as a pile of dust a fraction of the size of a penny. However, even this tiny amount is not ‘safe’. The precise 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. Exposures should be as low as practically possible, and not just kept below the WEL.
Assessment and control
Any task involving working on concrete, stone, or masonry by cutting, grit blasting, drilling, scabbling, breaking, or any similar process will cause silica dust. An enclosed area will increase the health risk to workers further, as will increasing the duration of exposure.7
If a task is generating silica dust then suitable control action will be expected. If it is possible to carry out works without using a method that creates excess dust, that should be the first option – but this is not always possible. If a dusty task is necessary, the first line of defence is control at source, for which there are various solutions available. Water suppression, a common method used on site and championed by the HSE’s ‘Time to clear the air’ campaign,5 is very effective for tools and processes that cannot be affected by moisture. However, there is also a number of disadvantages of using water suppression – for example: lack of a water supply can be a problem, although portable water bottles can be used.