The facts on Silicon Carbide Fibres

No estimates of current numbers of workers exposed to silicon carbide fibres in the EU are available. However, exposure is known to occur mainly in industries involved in the production and processing of silicon carbide and in the use of silicon carbide-containing materials.

Work-related exposure occurs mainly through the inhalation of airborne fibres generated during industrial processes such as furnace operation, crushing, grinding or machining. These fibres are very small and can remain suspended in the air, making them easy to breathe in.

Silicon carbide fibres are classified under the CLP Regulation as Carcinogenic Category 1B (may cause cancer in humans by inhalation). The carcinogenic potential is mainly linked to the fibre shape, size and persistence in the lungs.

Exposure to silicon carbide fibres can lead to serious health effects. The main type of cancer observed in workers is lung cancer, and there is also concern about mesothelioma.

Where risks occur

Occupational exposure to silicon carbide fibres occurs mainly in sectors where silicon carbide is produced or used, including in the manufacture of non-metallic minerals, refractory products, technical ceramic products, metal processing, machinery production and transport equipment.

Occupations at highest risk of exposure include furnace, crushing, milling or process operators, production workers, maintenance staff, machinists, metal grinders and polishers, and workers handling composite materials. These workers can be at risk of simultaneous exposure to other carcinogens, such as crystalline silica, PAHs, diesel exhausts, metals like hexavalent chromium or nickel, asbestos or welding fumes. Workers may be exposed during several stages of production and handling. Dust-intensive tasks may also contaminate clothing and lead to indirect exposure.

Exposure to silicon carbide fibres is also likely to occur in the production of motor vehicles and in the construction sector (e.g. abrasive blasting operators).

More about the substance

Silicon carbide fibres are solid inorganic fibres composed of silicon and carbon. They are extremely hard, chemically stable and insoluble in water and they can become airborne as dust and fibres during handling and processing.

They can occur unintentionally during manufacturing or be produced intentionally as whiskers for specialised uses.

The size and shape of the fibres are critical for health risk. Silicon carbide fibres typically have a diameter below 3 micrometres and a length above 5 micrometres. Because of their small size, similar to asbestos fibres, they can reach the deepest parts of the lung when inhaled and may remain there for long periods and are not easily cleared from the body.

Silicon carbide fibres are mainly used in high-performance composite materials where high strength, low weight, and resistance to extreme temperatures are required such as in aerospace engines, spacecraft vehicles, defence applications, industrial high-temperature equipment and other advanced engineering sectors.

Health risks that may occur

The main route of exposure to silicon carbide fibres is inhalation.

Short-term exposure can cause irritation and inflammation of the respiratory system.

Long-term exposure can cause lung cancer and possibly mesothelioma. Other severe non-cancer effects include pneumoconiosis and chronic lung disease, which can reduce lung function and cause breathing difficulties. All these diseases often have long latency periods, typically several decades between exposure and onset of the disease.

What you can do

Substitution should be considered wherever possible by replacing silicon carbide fibres with safer alternatives or processes. For some applications (e.g., thermal protection components, heat shields or hot gas ducts) oxide ceramic fibres or continuous carbon fibres have been proposed as substitutes.

Because of the properties of silicon carbide fibres, the main risk management focus should be on controlling airborne fibre release and preventing inhalation, rather than controlling vapours or liquids. Effective ventilation (general exhaust or local exhaust), dust suppression and containment are therefore essential measures in workplaces handling silicon carbide fibres. Organisational measures should include worker training, limiting exposure time, regular cleaning and exposure monitoring.

Workers should follow good hygiene practices and use personal protective equipment (like respirators) as a last resort when necessary and after introducing the possible engineering and organisational solutions. In some cases, however, respiratory protection of workers to inhalation of silicon carbide fibres is necessary, such as in furnace or process interventions, or in machining/grinding composite materials generating respirable fibre-containing dust. Employers need to ensure that breathing is not additionally physically demanding (e.g., use powered air-purifying respirators). It is highly recommended or mandatory, in accordance with national law or practice, that a fit test be performed on each person to ensure adequate protection. Respirators need to be regularly cleaned/replaced.

References: ECHA, IARC, RAC