Crystalline silica is the natural crystalline form of silicon dioxide (SiO₂), a mineral very common in the Earth’s crust.
It is found in many rocks (sandstone, granite, sand, etc.), and thus constitutes one of the major components of soil and mineral-based materials.
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Where is Crystalline Silica Found?
| Materials | Crystalline Silica Percentage in These Materials |
| Flint, siliceous sands | > 90% |
| Quartzite, sandstone | > 90% |
| Gravel | > 80% |
| Granite | 20% to 45% |
| Shales | 40% to 60% |
| Slate | 40% |
| Clays | 5% to 50% |
| Natural Diatomite | 5% to 30% |
| Dolerite | 15% |
| Iron ores | 7% to 15% |
| Marble | 5% |
| Limestone | 1% |
1. Natural Presence
Crystalline quartz (SiO_2) is one of the most common minerals. It represents the most widespread form of crystalline silica. In nature, it is found in abundance in:
Sandstone and granite.
Sand (of which it constitutes nearly 100%).
Consequence: The exploitation of sand or aggregates (via crushing and screening) systematically generates significant inhalable silica dust. Crystalline silica is therefore almost omnipresent in natural mineral materials, from rocks to sediments.
2. In Manufactured Materials and Construction
Crystalline silica is also very present in processed products. It is found particularly in the composition of:
- Of concrete, mortar, and facade coatings.
- Of brick and construction ceramics.
- Of glass and porcelain (produced from crushed quartz).
- Of certain industrial plastics and rubbers (used as a mechanical additive).
3. Specific Products (Diatomite): A Special Case
Some common products also contain silica. The most notable example is diatomaceous earth (kieselguhr), used as an absorbent or in filtration:
- Natural form: Although biological in origin, it can contain 0.1 to 3% crystalline silica.
- Calcined form: If diatomite is heated to very high temperatures, amorphous silica transforms into cristobalite. The crystalline silica content can then rise to 20–60%.
Sectors and Occupations Exposed to Crystalline Silica
As crystalline silica is so widespread in materials, many industrial sectors expose their employees to silica dust. According to a survey (SUMER 2017), approximately 358,000 employees in France are exposed to it at work. Historically, the main occupations affected are:
Construction and Public Works (BTP):
Any construction or renovation site. Demolition, concrete cutting (saw, chisel), drilling, hammering, planing, or sanding operations on structures release abundant concrete and stone dust (granite, sandstone, coatings, etc.) containing quartz.
Mines and Quarries:
Extraction and processing of siliceous rocks (granite, sandstone, siliceous). Crushing blocks and screening aggregates produce clouds of fine dust very rich in quartz.
Glass, Crystal, and Ceramics:
Manufacturing of glass and ceramics (tiles, tableware, insulators, etc.) from sand/quartz. Handling and spraying of silica are omnipresent in these sectors.
Foundry and Refractory Materials:
Dental Prosthetics:
Work on dental ceramics includes sanding and polishing phases that release crystalline silica in micronized form.
Other Affected Sectors:
The plastics and rubber industry uses crystalline silica as a filler (reinforcing agent), and even some industrial cleaning sites (diatomaceous earth) or sandblasting (“stripping”) operations expose workers to silica.
Thus, all professions working with concrete, stone, sand, diatomaceous earth, or fused silica must exercise vigilance. Since January 1, 2021, France has included these processes on its national list of carcinogenic processes. However, the national limit value was not modified on this occasion (it remains at 0.1/0.05 mg/m³).
Employers are responsible for identifying these risk situations and training teams in proper procedures.
The Health Effects of Crystalline Silica
The main route of entry for crystalline silica into the body is respiratory. Fine silica particles (diameter < 5 µm) penetrate deep into the lungs and remain there permanently.
The body therefore reacts by forming fibrous nodules: this is silicosis, an irreversible and potentially fatal lung disease.
Silicosis is characterized by progressive shortness of breath during exertion, evolving into severe respiratory failure. There is no curative treatment other than a lung transplant in severe cases, and the disease often continues to progress even after exposure ceases.
Recognition as an Occupational Disease
In addition to silicosis, chronic exposure to crystalline silica promotes bronchopulmonary cancer. The International Agency for Research on Cancer (IARC) classified crystalline silica in Group 1 (carcinogenic to humans) in 1997.
Numerous epidemiological studies have shown an increased risk of lung cancer in workers exposed to silica dust.
The World Health Organization estimates that silicosis can also be recognized as an occupational disease when it meets the criteria of table no. 25 of occupational diseases (general scheme).
In France, approximately 200 cases of silicosis are recognized as occupational diseases each year.
Exposure Limit Values and Regulations
Aware of these dangers, French regulations set very low occupational exposure limit values. The Labor Code (article R.4412‑149) defines the 8-hour OELV for crystalline silica: 0.1 mg/m³ for quartz and 0.05 mg/m³ for cristobalite and tridymite, measured on the respirable fraction of dust.
Similar rules exist for mixtures of siliceous dusts. Compliance with these thresholds is controlled by accredited bodies (almost always through air sampling).
Since 2015, work exposing workers to silica dust on construction sites has been subject to strict regulations (zero tolerance for non-compliance with instructions) via the “silica shock” from CNESST (Quebec) and CNAM (France).
As an international example, the American OSHA (2016) lowered its OELV to 0.05 mg/m³ (and recommends 0.025 mg/m³ as an action level).
At the European level, Directive (EU) 2017/2398 updated the Cancer Directive (2004/37/EC) by explicitly listing processes exposing workers to respirable crystalline silica as carcinogenic.
Finally, it should be noted that crystalline silica does not have a harmonized CLP hazard classification (no additional safety label), but its international recognition as a carcinogen associated with severe lung diseases reinforces the obligation for prevention.
Prevention and Protective Measures
Primary prevention consists of avoiding the formation of silica dust. The hierarchy of measures is as follows:
- Substitution: use an alternative, less siliceous material when possible. For example, replace quartz sand with non-siliceous aggregates, use synthetic coatings or mortars, etc.
- Containment and ventilation: carry out work in a confined environment or a ventilated negative-pressure cabin, close off exposed areas. Install local exhaust ventilation systems (hoods, canopies, cabins) to capture dust at the source.
- Wet methods: apply water to materials during sawing, grinding, or sanding to prevent dust from dispersing. Concrete sawing must be done with continuous watering.
- Source extraction: use portable tools equipped with integrated extraction, or connect machines to an industrial extraction system to eliminate dust directly at the tool’s outlet.
- Respiratory protection: when collective measures do not allow exposure to be lowered below the regulatory threshold, workers must wear appropriate respiratory protective equipment. This includes P2/P3 filtering masks (or equivalent) or supplied-air respirators, depending on the concentration. Devices must be certified (e.g., NIOSH or CEN) and used within a respiratory protection program that includes training and monitoring.
In addition, employee training and information are mandatory: they must be aware of the risks associated with silica and know how to use protective measures. Regular medical check-ups (respiratory examinations, chest X-rays) are required for exposed individuals (individual post-occupational follow-up as stipulated by article D.461‑23 of the CSS). Finally, certain highly exposing uses are subject to specific rules (for example, dry sandblasting is strictly regulated, with the abrasive not allowed to contain more than 5% free silica in an open booth).
Key Takeaways on Crystalline Silica
In summary, crystalline silica is omnipresent in rocks and construction materials. Professionals in construction and public works, extractive industries, and manufacturing are exposed to it daily, hence the importance of risk awareness and prevention.
The health effects (silicosis, lung cancer) are severe and irreversible, which justifies very strict regulations (OELV, classification, prohibition of work for minors, etc.).
