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Particle sizes

The graphic above shows by means of examples which particle sizes can be generated during various production processes.

Settling particles

Coarse particulates between 1mm and 0.1mm (=100µm) in size are visible to the naked eye. Members of this fraction are, for instance, heavy industrial dust, sand, mist and hair. Smaller particulates with less than 100µm in diameter are already only visible by means of an optical microscope, such as pollen, cement dust, carbon dust, coarse metallurgic dust or generally settling dust with a diameter of more than 1µm. These fractions match filter classes G3-G4, but they will also be collected by the notably more efficient filter classes F5-F9 and H10-U17.

Airborn particles

Particulates that will not settle but stay suspended in the air are less than 1µm in size. Some bacteria are smaller than 1µm and belong to this fraction, however also metallurgic dust and oil mist occur within this range. Particulates of a size of more than 0.1µm but less than 1µm are covered by filters of filter classes F5-F9, where filters rated H10-U7 will also collect these particulates.

Ultra-fine particles

Particulates smaller than 0.1µm are merely visible by means of a scanning electron microscope. Fine oil aerosols are sized between 0.01µm and 0.1µm; tobacco smoke and asbestos are partly even smaller than 0.01µm. Most viruses and fine metallurgic dust belong to the fraction 0.001µm to 0.1µm. In order to collect these particulates, only HEPA and ULPA filters of classes H10-U17 remain suitable. Particles smaller than 0.01µm might be collected by activated carbon on a molecular basis.

Hazardous gases

Gas molecules and pesticides are rarely larger than 0.001µm. They are airborn and can penetrate into the alveoles in case they are inhaled. The only suitable filter medium for these pollutants is activated carbon.