Frequently Asked Questions
All about Crystalline Silica
What is crystalline silica?
Crystalline silica, also known as silica or quartz, is a mineral which is present in almost every type of rock. It is one of the most common minerals on the planet, making up around 12% of the earth’s crust.
Silica is synonymous with silicon dioxide (SiO2). Silicon and oxygen are the two most abundant elements in the earth’s crust. Silica is commonly found in nature as sand. Silica exists in many different forms that can be crystalline as well as non-crystalline (amorphous).
Crystalline silica is hard, chemically inert and has a high melting point. These are prized qualities in various industrial uses.
Quartz is the most common form of crystalline silica and is the second most common mineral on the earth’s surface. It is found in almost every type of rock i.e. igneous, metamorphic and sedimentary. Since it is so abundant, quartz is present in nearly all mining operations.
What is crystalline silica used for?
Crystalline silica really is one of the building blocks of modern life. It is used in millions of different essentials we use on a daily basis – our computers and phones, cars and buses, roads and railways, glass and ceramics, and even our homes.
Crystalline silica is an essential component of materials which have an abundance of uses in industry and are a vital component in many things used in our everyday lives. It is impossible to imagine houses without bricks, mortar or windows, cars without engines or windscreens, life without roads or other transport infrastructures and everyday items made of glass or pottery.
Industrial silica is used in a vast array of industries, the main ones being the glass, foundries, construction, ceramics, and the chemical industry.
Silica in its finest form is also used as functional filler for paints, plastics, rubber, and silica sand is used in water filtration and agriculture.
Other examples of everyday uses include the construction and maintenance of an extensive range of sports and leisure facilities.
Crystalline silica is also irreplaceable in a series of high-tech applications, for example in optical data transmission fibres and precision casting. It is also used in the metallurgical industry as the raw material for silicon metal and ferrosilicon production. Another specialized application is in the oil extraction.
Altogether there are hundreds of applications of industrial silica in our daily life. Silica products have become so obvious to us that we don’t even know they are being applied.
Why is crystalline silica used?
Crystalline silica has prized physical and chemical properties. It is inert, extremely hard wearing and temperature resistant, so has is useful in lots of products. Together, these properties make it extremely versatile.
Is crystalline silica replaceable?
No. For some applications (eg. glass manufacture) there is no alternative to crystalline silica. In other applications, only crystalline silica can provide the physical and chemical properties necessary for products to function well. Where alternative raw materials do exist, they often contain a proportion of crystalline silica.
The most common form of silica, quartz, is an abundant, natural substance on our planet and we are all exposed to it every day. It makes up 12% of the earth’s crust and, besides being present naturally in our environment, it is also one of the vital raw materials for modern civilisation.
On average, every person in Europe consumes around 400 tonnes of minerals in their lifetime, with most minerals containing quartz. Can you imagine life without houses, workplaces, schools, hospitals, roads, cars, glass, ceramics…?
Even if we did find alternatives to silica, any benefit to health would be doubtful as, in most cases, this natural substance would have to be replaced by a synthetic one manufactured at greater cost, especially in terms of energy and raw materials.
The health hazards associated with silica dust are well known and well managed. The focus is on implementing good practice measures in quarries to minimise the generation of airborne dust, not just for the benefit of workers but also to minimise any impact on the surrounding environment.
Which rocks contain crystalline silica?
Almost every type of rock contains crystalline silica in some form, but the most commonly known is quartz, which is a form of crystalline silica. Other commonly used materials which contain crystalline silica include concrete, ceramics, glass, and clay. Overall, crystalline silica makes up around 12% of the earth’s crust.
Constituting 12% of the Earth’s crust, quartz, the most common of the nine crystalline silica polymorphs, is the second most abundant mineral in nature. As a consequence, it is everywhere in our daily environment: on beaches and roads, in the fields, on athletics tracks and in the garden.
All mining and quarrying activities involve crystalline silica. Indeed it is present in all naturally occurring materials that have been mined from the ground for thousands of years: sand, gravel, dimension stones, metallic and non metallic mineral ores. Therefore, from traces to significant amounts, crystalline silica is present in commodities which are vital raw materials for modern technology and everyday life (see EUROSIL website chapter “Applications”).
This led a socio-economic survey of crystalline silica usage to conclude that “if man wishes to live in silica free environment he must move to another planet” (B. Coope, 1998).
Is this the same silica that is used in product packaging?
Silica gel sachets, which you often find in packaging, contain small beads that are manufactured via a process that starts with silica. The small beads are used as a desiccant — meaning that they absorb water very quickly — to keep products in the packaging dry.
Respirable Crystalline Silica – a risk to workers
Is crystalline silica poisonous?
No. If you touch or are around crystalline silica in the everyday natural environment, it is completely inert and safe. Crystalline silica can only cause a potential health risk when rocks, minerals and other products containing it are used in industrial processes like cutting, drilling, crushing etc. Under these conditions, a very fine dust airborne called Respirable Crystalline Silica (RCS) can be produced, which if inhaled at high levels over many years, can cause lung diseases.
What does RCS stand for?
RCS stands for ‘Respirable Crystalline Silica’, a very fine airborne dust produced during industrial processes using certain rocks, minerals or other products containing crystalline silica.
The term Respirable Crystalline Silica relates to airborne dust in workplace atmospheres. When considering dust, three dust fractions are of main concern: the inhalable, thoracic and respirable dust fractions. The respirable dust fraction corresponds to the proportion of an airborne contaminant, which penetrates to the deep lung (alveoli). Respirable crystalline silica enters the body when dust containing a proportion of crystalline silica is inhaled. Respirable crystalline silica is the fraction of airborne silica dust which can be of concern to health when inhaled. For this reason, national occupational exposure limit values for crystalline silica apply to the respirable dust fraction.
This fraction normally represents 10 to 20% of the inhalable dust fraction, but the proportion can vary considerably. Respirable particles are tiny, measuring only a few microns (thousandths of a millimetre) in diameter. Airborne respirable dust particles are generally too small to be seen with the naked eye unless they are illuminated under a beam of intense light.
Respirable crystalline silica enters the body when dust containing a proportion of crystalline silica is inhaled. When the particle size range of the dust is sufficiently small (such that the particles fall within the respirable fraction), the dust will travel deep into the lung (pulmonary alveolar (gas exchange) region of the lung). It is at this point that respirable crystalline silica can cause health effects.
What is the danger of RCS?
When rocks, minerals and other products containing crystalline silica are used in industrial processes like cutting, drilling, crushing etc., respirable dust of crystalline silica (RCS) can be produced. If high levels of RCS are inhaled regularly over many years at high intensity, it can irritate the lining of the lungs, and cause lung diseases.
Silicosis is one of the world’s oldest known occupational diseases and is caused by the inhalation of respirable crystalline silica (Stacey P. 2005). It is one of the most common types of pneumoconiosis. It is a nodular progressive fibrosis caused by the deposition in the lungs of fine respirable particles of crystalline silica.
Silicosis is an occupational disease, meaning that it only affects people exposed in the workplace. Environmental exposures to silica dust are much lower than those encountered in the workplace and are not sufficiently high to cause this occupational disease.
Future cases of silicosis can be reduced by implementing appropriate measures to reduce exposure to silica-containing dusts. Such measures include improved work practices, engineering controls, respiratory protective equipment and training programmes.
The disease has a long latency period. The new cases of silicosis registered today are due to exposure of three or four decades ago.
The resulting scarring of the innermost parts of the lungs can lead to breathing difficulties and, in some cases, death. Larger (non-respirable) particles are more likely to settle in the main airways of the respiratory system and may be cleared by mucus action (HSE 1998).
Silicosis can vary greatly in its severity, from “simple silicosis” to “progressive massive fibrosis”. Generally, three types of silicosis are described in literature (EUR 14768; INRS 1997):
- Acute silicosis occurs as a result of extremely high exposure to respirable crystalline silica over a relatively short period of time (within 5 years). The condition causes rapidly progressive breathlessness and death, usually within months of onset.
- Accelerated silicosis can develop within 5 to 10 years of exposure to high levels of respirable crystalline silica.
- Chronic silicosis is often described as the result of exposure to lower levels of respirable crystalline silica, occurring over longer periods of time (exposure duration greater than 10 years).
Although it is in decline, silicosis is not yet completely eliminated.
Peaking with industrialisation at the beginning of the 19th Century, silicosis prevalence has since seriously declined (more than 90% since 1960). The main reasons of this decline are:
- Closure of coal mines
- Health surveillance and medical progress in early diagnosis
- Continuous improvement of hygiene measures in the workplace: development of new processes and ventilation systems, improved personal protective equipment, greater awareness of health and safety requirements (such as the introduction of occupational exposure limits)
European silicosis figures are difficult to compare. Although some national data are available, no harmonised European silicosis statistics yet exist. Due to the differences in Member States’ social security approaches, notably in occupational disease recognition criteria and compensation systems, any comparison is difficult and the total number of silicosis cases reported annually in the EU is difficult to assess.
According to World Health Organisation estimates, the global number of silicotics in the world could reach a total of 5 million individuals. The situation according to health experts is really worrying in developing countries, but almost under control in the EU.
Whatever the exact figures, and in spite of its continuous decline, silicosis remains an occupational health issue.
Occupational exposure limits have been implemented for respirable crystalline silica to help protect workers from occupational diseases. These limits are set primarily on the basis of scientific evidence but may also take into account social, economic and measurement factors. Strict observance of occupational exposure limits will reduce the risk of disease to a low level but, for some susceptible individuals who are exposed for many years, there may still be a residual risk. It is important that exposure to respirable crystalline silica dust is reduced to the lowest levels possible.
Therefore, silicosis and lung cancer prevention programmes such as the European “Social Dialogue Agreement on workers’ health protection through the good handling and use of crystalline silica and products containing it“ are very important. This Agreement, which promotes strict compliance with existing regulatory limits and requires implementation of good practice preventive measures to further reduce dust exposure, should be highly effective in eliminating occupational diseases due to RCS exposure. Full information is available at www.nepsi.eu.
RCS causes lung cancer by an indirect mode of action via inflammation, i.e. silicosis, thus minimising silicosis risk will also minimise or even eradicate lung cancer risk due to RCS.
This is the outcome of a recent hazard assessment of Respirable Crystalline Silica health effects which has been commissioned to a team of scientific experts. Two reports were produced:
- Review and Hazard Assessment of the Health Effects of Respirable Crystalline Silica (RCS) Exposure to inform Classification and Labelling under the Global Harmonised System: Overview Report (Borm P, Brown T, Donaldson K, Rushton L, 2009); and
- Review of the Literature of the Health Effects of Occupational Exposure to Crystalline Silica: Silicosis, Cancer and Autoimmune Diseases (Brown T, Rushton L, 2009)
A summary of these reports by Dr Peter Morfeld (Institute for Occupational Medicine of Cologne University, Institute for Occupational Epidemiology and Risk Assessment of Evonik Industries, Essen, Germany) is available here.
A suspicion of lung cancer occurrence among workers exposed to crystalline silica was evoked at the end of the 1960s. However, confirmation of a link between silica exposure and lung cancer was generally considered impossible until the 1980s. In 1987, the International Agency for Research on Cancer (IARC) evaluated crystalline silica as a probable human carcinogen (Group 2A – sufficient evidence in animals but limited evidence in humans). This opinion was based upon the findings that under laboratory conditions some quartz samples could be carcinogenic for rats (but not for other rodent species).
Over the next decade, no further conclusive human evidence was brought forward but experts agreed that an excess of lung cancer could be observed in silicotics (i.e. people already having silicosis).
In 1997, the IARC re-evaluated crystalline silica and concluded on the basis of literature review that inhaled respirable crystalline silica from occupational sources is carcinogenic to humans, this evaluation was confirmed in 2011 in Monograph 100C.
Should I be worried about RCS?
RCS only poses a risk to people who are working in industrial workplaces, where products containing crystalline silica are used in processes such as cutting, drilling and crushing. RCS caused by these processes does not spread beyond the direct environment of the industrial activity. If you do not work in these environments, you will not be exposed to high levels RCS.
And the risk to people working in these environments can be mitigated by following simple and easy to implement health and safety good practices. Since 2006, these simple good practices have been freely available online to all industries where RCS poses a risk, through a body called NEPSI – which was set up by industry, unions and the European Commission to protect workers health.
You will find more information on the Protecting Workers page.
What are the potential health effects caused by long-term RCS exposure?
Long term exposure to high levels of RCS dust can cause lung fibrosis, commonly known as silicosis. The main symptom of silicosis are a cough and shortness of breath. Severe cases can lead to fatigue, chest pain, loss of appetite, and weight loss. People with silicosis are also at higher risk of lung cancer. The risk of silicosis from workplace exposure to RCS is the reason we have good practices in place to mitigate the risk to workers’ health.
Will I become ill if I am exposed to RCS for a short time?
No. RCS only causes lung diseases in people who have been exposed to high levels of the dust regularly for many years.
Is there such a thing as a safe level of RCS?
The EU Directive on “Protection of workers from exposure to carcinogens or mutagens at work” recognises a limit of RCS as 0.1 mg/m³ — although you will only ever come close to this limit in industrial workplaces where products containing crystalline silica are used in industrial processes. The risk from RCS in the workplace can be mitigated by following simple and easy to implement health and safety good practices.
I live near a quarry / factory / plant — am I at risk from RCS?
No. The body is only impacted by inhaling high levels of RCS over many years, meaning that only people working in the direct vicinity of industrial processes are at risk. There is a natural background level of RCS in the air, but the levels are so low that it poses no risk – and a quarry / factory / plant near you does not increase levels of RCS beyond that natural background level.
Living near a quarry does not put you at any risk of getting cancer.
Independent studies conducted notably in the UK by the government health and safety laboratory, HSL on behalf of the Health and Safety Executive (HSE) confirm that quarrying does not have any significant impact on air quality outside the quarry boundary. Furthermore, there is no evidence to suggest any link between quarrying and lung disease among members of the general public who live nearby.
According to Great Britain’s Health and Safety Executive (HSE): “No cases of silicosis have been documented among members of the general public indicating that environmental exposures to silica dust are not sufficiently high to cause this occupational lung disease. The weight of evidence suggests that exposures to respirable crystalline silica (RCS) insufficient to cause silicosis, would be unlikely to lead to an increased risk of lung cancer.”
Remember that silica sand isn’t just found in quarries – it’s also what makes up the beaches on our coastline. People who live on the sea front don’t get cancer just because they live near the beach.
On rare occasions, when it’s very dry and windy, quarry operators have to take extra precautions to help prevent sand being picked up by the wind. This usually involves using water sprays and wetting down roads, quarry faces and stockpiles. In some cases, it may be necessary to stop work temporarily. Despite the best efforts of quarry operators, in extreme weather conditions it may be impossible to prevent some sand from being picked up by the wind.
Even if sand is being blown onto your property it may be a nuisance but there’s no need to worry about it affecting your health. Measurements taken around quarries indicate that even on dry and windy days there is no significant impact on air quality in terms of fine particulate levels at residential properties located close to quarries. In simple terms, the sand in the quarry is made up of particles which are too big to be of any risk to health.
Quarries are indeed a source of PM10 and PM2.5 particulates. However, particles of this size are emitted by a variety of sources, including road vehicles, domestic heating (coal and wood fuels), industrial combustion sources and other industrial production processes. There are natural sources too, which contribute to ambient concentrations e.g. sea salt at coastal locations.
Various measures are taken to prevent airborne dust being generated by trucks when they are carrying mineral products. Loads are enclosed, sheeted or packaged not just to prevent loss in transit but also to keep them in good condition until they reach their destination.
Where necessary, quarry operators also take special precautions to keep the roads clean outside their quarries. Many quarries have truck washing facilities and wheel washes and some even use road sweepers to keep the roads clean around their site entrances.
The only people whose health may be at risk from silica dust are workers in industrial processes where silica products are produced or handled and where lots of airborne silica dust is generated. This dust needs to be very fine to cause any health risk – in fact it needs to be so fine that the particles of concern cannot be seen with the naked eye. If this dust is not properly controlled then workers may be at risk of lung disease, although it takes years of daily exposure at high levels before the risk becomes significant.
These workplace situations are regulated under health and safety law and there are strict limits on personal exposure which must not be exceeded. Compliance with good practice in silica dust control and with regulatory exposure limits will help to minimise any health risks.
Does construction / building work create RCS?
Some construction work does produce RCS, especially if it involves cutting, drilling or crushing materials which contain crystalline silica. In general, it is high energy mechanical processes that create the most RCS dust. The risks can be minimised through good design (e.g. reducing how many times a material needs to be cut) and by following good practices for dust prevention and control.
What is being done to protect workers
What can be done to limit exposure to RCS for workers?
Thankfully crystalline silica-related disease can be prevented through the application of good practices – for example using ventilation and air filtering devices in industrial workplaces, and using respirators when engaging in industrial processes which produce a lot of RCS. These good practices are freely available online through NEPSI – a body set up by industry, unions and the EU to advise on protecting workers’ health from RCS.
What is the new EU legislation on carcinogens about? Why is this an issue now?
The EU Directive 2017/2398 on “Protection of workers from exposure to carcinogens or mutagens at work” implements a set of legal limits on exposure to certain substances in industrial workplaces. One of the substances recognised in the legislation is RCS, which is known to cause lung diseases in workers who are exposed high levels of it regularly for many years.
However, this is not a new issue – lung disease from workplace exposure to RCS it has been known and understood for centuries. That is why the industrial minerals industry, and other industries which use products containing crystalline silica, already have health and safety measures in place to protect workers from exposure to RCS. Following good practices brings exposure to RCS below the new legal limits implemented in the EU Directive, and mitigates the risk to workers’ health. These good practices are freely available online through NEPSI – a body set up by industry, unions and the EU to advise on protecting workers’ health from the potentially damaging effects of long-term RCS exposure (see the NEPSI website).
Notably Directive 2017/2398 has no impact upon product classification and labelling. The Directive is put forward only in the context of occupational workers’ health protection legislation. In the EU the classification and labelling of products is ruled by other separate legislation (the CLP Regulation 1278/2008). There is no direct link between these two legislative frameworks. Directive 2017/2398 addresses respirable dust generated by work processes, not the substance itself. Crystalline silica placed on the market is subject to the classification obligation under Regulation (EC) 1272/2008, while crystalline silica dust generated by a work process is not placed on the market and therefore is not classified in accordance with that Regulation.
Where can I find more information about crystalline silica and RCS?
Further information about crystalline silica and RCS is available here on this website. Good practices for companies are available on the NEPSI website. The content of this website is summarized in the “Using Crystalline Silica Safely White Paper“.