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Classification of pollutants
Filter standards
Particle sizes
Settling time of particulates
Conversion table
Cleanroom classes
Laser machining

Settling time

The graphic placed below shows the time particles spend in the air before they will settle. These settling times apply for a room of 1m height.


Average settling times of particles dependent of their size between <0.1µm and 100µm


Hazardous ultra-fine particles remain in breathable air

Particles of a size of 15µm to 100µm will settle within one minute in case they are not dispersed by air movement. In larger rooms, settling time will increase respectively.
Particles sized less than 10µm will already take about 3 minutes to settle; at a size of 5µm, settling will take 8 minutes. As the settling time increases non-linear, particles with a diameter of 1µm will already take 4 to 5 hours to settle. Particles smaller than 1µm will not settle at all but stay airborn permanently.

Airborn particles pose a health risk

Thus, particular dangerous particles, i.e. particles of especially small size, will for a long time stay suspended in the air from where they can be inhaled. Health risk is greater when the inhaled particles are smaller. A notable discovery is that the chemical composition of particles is not deciding for their negative effects on health, as also chemically intoxic particles can penetrate deep into the respiratory tract and sometimes even into the alveoli. Fine particulate matter is suspected to cause cancer, disregard any direct toxic effects. In any case, bronchial tubes and lung are harmed as the respiratory system is blocked up by fine dust. Depending on the application, fine particles will not only impair the staff's health but also product quality.

Coarse particle are dangerous for man and machinery

Whereas small particles will stay suspended in the air for an especially long time and, in this way, pose a certain hazard, coarse particles will settle fast and pollute surfaces, machinery parts and, depending on accessibility, the insides of machinery. Air movement can disperse these particles and cause the possibility of them being inhaled, posing further stain of the respiratory tract.