What Is Crystalline Silica?
Crystalline silica (silicon dioxide or SiO₂) is a naturally occurring mineral found abundantly in the Earth’s crust. It exists in both amorphous and crystalline forms—commonly as quartz and cristobalite. The version of concern under California Proposition 65 is airborne particles of respirable size, which are fine enough (≤10 micrometres) to be inhaled deep into the lungs.
Why the Warning?
California’s Proposition 65 mandates businesses to warn individuals of significant exposure to be listed substances known to cause cancer or reproductive harm.
Crystalline silica (respirable particles) is listed for its cancer-causing potential, specifically linked to lung cancer.
Where Is Crystalline Silica Found?
You may encounter it in:
Rocks like granite, marble, limestone, and sandstone
i. Construction materials: concrete, cement, bricks, mortar, manufactured stone
ii. Industrial products: ceramic, glass, plaster, wood filler
iii. Art materials: dry or powdered clays, glazes, some paints
How Does Exposure Happen?
When these materials are cut, ground, polished, or sanded, tiny respirable silica particles are released into the air. You can inhale them unknowingly while:
1. Sandblasting or polishing countertops
2. Sanding plastered walls
3. Cleaning up powdered clays or glazes without proper dust control
Even shaking out dusty clothes indoors can cause inhalation.
How to Reduce Exposure?
Here are effective precautions to minimize the risk:
i. Work outdoors when using silica-containing materials
ii. Use wet methods to suppress dust during sanding or cutting
iii. Wear a respirator—and ensure its properly fitted and maintained
iv. Use HEPA vacuums or wet rags instead of sweeping or blowing dust
v. Change clothes before entering your car/home if exposed
vi. Keep children away from dusty areas
Avoid using brooms, fans, or compressed air for cleanup. These spread fine particles into the air.
Fact Sheet Release
This Proposition 65 fact sheet on Crystalline Silica (Airborne Particles of Respirable Size) was published by OEHHA in June 2025.
Reference: Crystalline Silica - (Airborne Particles of Respirable Size) - Proposition 65 Warnings Website
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