Silica dust: a hidden danger

Many natural organic compounds found on construction sites and other industrial working environments contain silica. Disrupting these materials through cutting, sanding and carving can release dust that is fine enough to inhale into the lungs and is too small to be visible to the naked eye in naturally lit areas.

Photograph: iStock/photovs

This fine dust is known as respirable crystalline silica (RCS) and is a common by-product of many manufacturing tasks. For instance, brick and tile manufacturing, working on ceramics, stone working, and foundry work can all produce airborne silica particles, and RCS is also produced when working on silica-containing materials like concrete, mortar and sandstone in construction – such as cutting up concrete blocks or abrasive blasting of sandstone. 

Every year, an estimated 600,000 workers are exposed to silica in the UK¹, and the Institution of Occupational Safety and Health (IOSH) estimates that in Europe, as a whole, 81 per cent of those exposed are employed in construction or in manufacturing products used in construction².

Thousands of these workers suffer from respiratory conditions and lung diseases, including lung cancer, as a result of direct exposure to silica dust. In 2021, the Health and Safety Executive (HSE) found that 12,000 deaths each year, in the UK, are estimated to be linked to past exposure to dust and chemicals at work³. HSE expects the actual number of cases to be much higher than this estimate, as silica dust health monitoring is under-reported in industry.

Indeed, while exposure to silica dust might not be talked about as much as asbestos, the impact can be just as devastating to those affected.

Inhalation of RCS can cause the development of the following lung diseases:

• Silicosis– an irreversible scarring and stiffening of the lungs which makes breathing more difficult and increases the risk of lung infections. Silicosis generally follows exposure over a long period of time, but extremely high exposures can lead to rapid ill health. The NHS defines silicosis as “a long-term lung disease caused by inhaling large amounts of crystalline silica dust, usually over many years”, while HSE refers to silica as the biggest risk to construction workers after asbestos.
• Chronic obstructive pulmonary disease (COPD)– a group of lung diseases, including bronchitis and emphysema, resulting in severe breathlessness, prolonged coughing and chronic disability. It can be very disabling and is a leading cause of death. Bronchitis is an inflammation of the bronchial tubes that carry air to the lungs, which causes a harsh cough, shortness of breath, wheezing, a low fever and chest tightness. Emphysema is a lung disease which results in shortness of breath due to destruction and dilatation of the alveoli.
• Lung cancer–this can be caused by heavy and prolonged exposure to RCS dust. When someone already has silicosis, there is an increased risk of lung cancer.

What does the law require?

The Control of Substances Hazardous to Health Regulations 2002 (COSHH) set out the measures employers must take to protect their employees from exposure to substances that may harm their health, including silica dust. However, unlike asbestos, there are currently no regulations specific to controlling exposure to silica dust.

Due to the potential harmful health effects of silica dust exposure at work, the Workplace Exposure Limit (WEL) for RCS is comparably lower than that allowed for other substances, at 0.1mg.m-3 (milligrams per metre cubed) over a period of eight hours. Paraffin wax fumes, for example, has a WEL of 2.0 mg.m-3 (a WEL is the maximum allowed concentration of a hazardous substances in the air at work, averaged over a set period of time).

Under the COSHH regulations, employers must:

• Assess the risk of exposure to hazardous substances, like RCS – the risk assessment should consider: the hazardous properties of the substance, the amount of exposure expected and the effectiveness of the existing or planned exposure control measures
• Ensure that the exposure of employees to substances hazardous to health is either prevented or, where this is not reasonably practicable, adequately controlled
• Monitor working environments where hazardous substances are present or created and ensure adequate control measures are in place to either eliminate or adequately reduce exposure to protect workers from harm.

Controlling the risks

The first step towards protecting employees and workers is identifying the materials and substances that pose a respiratory health hazard.

A full review of all materials and work processes should be carried out, including referring to any available Material Safety Data Sheets (MSDs). MSDs are a great way to collate and digest information, as they include identification of the hazards, and advice on the safe use of substances, suitable exposure controls and appropriate personal protective equipment.

The long latency of diseases associated with RCS means that many employers and employees fail to understand – or overlook – the need to manage and control silica exposure until it is too late. It is therefore vital that employers educate themselves about the risks and appropriate exposure controls and ensure workers are given adequate information and training so they also understand the dangers from RCS and how to protect themselves. Employers should therefore follow the advice of initiatives like The Construction Dust Partnership (CDP), which provides guidance on good practice for controlling exposure to RCS and other dusts, which may go further than the minimum required by law.

Kevin Williams is respiratory manager at Arco Professional Safety Services. Photograph: Arco Professional Safety Services

Once a suitable risk assessment for hazardous substances like RCS has been completed and the potential hazards and risks have been identified, suitable preventative and protective measures should be implemented. Although the most suitable kind of exposure controls will depend on factors like the type of work being carried out and the materials being worked on, the first step should be to try to avoid the need to use or work on materials that contain silica dust – for example, by substituting them with silica-free alternatives.

However, if this is not possible, employers should:

Reduce the dust – before any work begins, suitable working methods and procedures for preventing airborne dust arising in the first place should be considered – including selecting building materials that either do not contain silica or contain lower amounts.

Use engineering controls – to remove or reduce employee exposure to RCS. Possible options include using less powerful tools that generate less dust when working on materials containing RCS; water systems that spray water onto a tool to reduce dust emissions; and ‘on-tool’ dust extraction systems, that capture and remove dust as it is being produced. In particular, the following approaches are recommended for minimising the amount of airborne dust generated during tasks like cutting, grinding, drilling, sanding and polishing RCS-containing materials:

• Water suppression – water needs to be used correctly to suppress dust clouds. There should be a constant supply for the full duration of work
• Vacuum extraction – this is a type of local exhaust ventilation (LEV) that fits directly onto tools and is a common way to control dust generation. All LEV systems work in the same way by capturing and extracting contaminated air at source, preventing dust from being breathed in and transporting the dust safely away to an emission point and to a filter or scrubber.
• Provide PPE – in the form of respiratory protective equipment (RPE), if the risk cannot be adequately controlled using measures like LEV and water suppression. However, it is essential to select the correct type of RPE, so employers must have a suitable RPE management programme to ensure the RPE is appropriate for the task and worker; workers are given face-fit testing for tight-fitting RPE; training is provided on the correct use of RPE; and the RPE is regularly inspected for faults and properly maintained. If there is any uncertainty about the correct selection and use of RPE, experts should be consulted.

Dust monitoring

It may also be necessary and appropriate to carry out monitoring of employees’ exposure to RCS to ensure the control measures are effective and the WEL for RCS is not being exceeded, including taking measurements of dust levels in the work area. However, historically, some companies have decided against carrying out appropriate monitoring practices as they believed that dust is common in construction and monitoring methods are expensive.  

In fact, dust monitoring is vital and new technologies now enable employers to determine real-time exposure levels to silica. Previous manual measurements of exposure were always reliant on gravimetric assessment, which required technical equipment that needs to be calibrated and placed in the respirable zone. The sample then had to be sent away to a laboratory for analysis and would only give results days or weeks post-analysis.

Now, real-time monitors can offer feedback instantly and can even form part of a control strategy if linked to alarm triggers or a system to slow or stop a dust-generating mechanism, should harmful levels be breached. 

Carry out regular employee health surveillance

Health surveillance – such as periodic health questionnaires and lung function tests for employees – may be required if workers are at risk developing ill health like silicosis from exposure to RCS. Health surveillance can identify early signs of exposure, provide early detection of breathing problems or lung damage and help the employer monitor the effectiveness of the control measures.

As part of a series of toolbox talks, Arco has produced a video on respiratory protection and advice for those working with wood dust and silica dust. Arco also submitted evidence to the recent inquiry into the prevention of silica-related occupational disease by the All-Party Parliamentary Group (APPG) for Respiratory Health.

Kevin Williams is respiratory manager at Arco Professional Safety Services.

For more advice see:

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References

1. iosh.com/media/11261/appg-silicosis-report-01-23.pdf pg. 8
2. iosh.com/media/11261/appg-silicosis-report-01-23.pdf pg. 8
3. hse.gov.uk/statistics/overall/hssh2021.pdf