Question

what is the size of respirable dust ?​

Answer 1

Relative to total airborne particles, the particle size having 50% penetration for the thoracic and respirable fractions are 10 μm and 4.0 μm (all particle sizes are aerodynamic diameter unless expressed otherwise), respectively [2,3].

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Answer 2

respirable dust has been defined 2 different ways in documents like glossary of mining terms, IUPAC Glossary of terms used in toxicology 2nd edition