For the purpose of dust monitoring and air sampling and potential health effects the following particle size fractions are defined and sampled:
Inhalable dust – is that fraction of a dust cloud that can be breathed into the nose or mouth. Examples of dusts for which any inhalable particle is of health concern include certain hardwood dusts (which may cause nasal cancer), and dusts from grinding lead-containing alloys or sanding lead paint (which can deposit anywhere, be absorbed and cause systemic poisoning)
Thoracic dust – is that fraction that can penetrate the head airways and enter the airways of the lung. Examples of dusts for which this fraction is of particular health concern include cotton and other dusts causing airway disease
Respirable dust – is that fraction of inhaled airborne particles that can penetrate beyond the terminal bronchioles into the gas-exchange region of the lungs (alveoli). Examples of dusts for which the respirable fraction offers greatest health hazard include crystalline silica (eg. quartz) when cutting into rocks, sandstone, concrete; cobalt-containing and other hard metal dust produced by grinding masonry drill bits; and many others.
Workplace Exposure Standards for Dust to Compare with Dust Monitoring Results
Workplace exposure standards (WES) are set for many airborne particulates including those with higher toxicity as inhalable dust or respirable dust mostly as the 8-hour time weighted average (TWA)) concentration of the substance within the breathing zone of the worker. Safe Work Australia recommends that “Where no specific exposure standard has been assigned and the substance is both of inherently low toxicity and free from toxic impurities, exposure to dusts should be maintained below 10mg/m3, measured as inhalable dust (8 hour TWA).” For higher toxicity particles such as quartz, Safe Work Australia WES is 0.1mg/m3 as 8-hour TWA (respirable crystalline silica (Quartz)).