Dangerous airborne dust particles are defined in a size range between 2.5 and 10 microns.
PM2.5 (Less than 2.5 microns)
PM10 (less than 10 microns)
These respirable airborne size particles are able to enter and deposit within deep tissue parts of the lung over time causing lung disease. This is due to the human body own mechanisms which are not able to capture or expel these invisible size particles.
In regards to occupational health and safety there is WHS legislation which requires the use of HEPA filters specially when there may be naturally-occuring asbestos in earthworks or in minerals processing.
Asbestos fibres range between < 3 microns in diameter and > 5 microns in length (Airborne fibres).
Coal dust particles range between 1 to 100 microns
Cement dust particles range between 3 to 100 microns
Breathesafe distributes long life cabin pressuriser systems with HEPA filters to remove hazardous respirable fraction particles with the efficiency of removing 99.97% of particles in the 0.3-micron range. This is the benchmark for High Efficiency filters as tested per EN1822 which is the European Standard for air filters used in cleanrooms for pharma and electronics manufacturing.
(H13 or H14 Grade each is individually tested after manufacture as Per EN1822)