1.4. What is respirable crystalline silica (RCS)?

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.

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