Can respirable dust be seen with the naked eye?

• A. Yes
• B. No
• C. Sometimes
• D. Only with special equipment

Answer: (B)

Respirable dust particles are extremely small, typically 10 micrometers or smaller, so they’re invisible to the naked eye in normal conditions. Even if you see dust in the air, that visible haze is usually made up of larger particles that aren’t respirable. The dangerous portion—the respirable fraction that can reach the deep parts of the lungs—cannot be seen without instruments. To determine how much respirable dust is present, you rely on sampling with specialized equipment (like a respirable dust sampler), not on what you can visually observe. That’s why respirable dust cannot be seen with the naked eye.