Settling time of particulates

The weight and size of a particle is of particular importance for its settling time. The smaller and lighter the particles, the greater the possibility that they will remain floating in the air helped by thermal currents and vortices. The following figure shows how long particles float in the air before they settle. The settling times apply for droplets or particles at a height of one metre.

Particulate matter is a health risk

The finer the particles, the greater the health risk that they pose. It is important to note that the chemical composition of fine dust is not the only decisive factor in assessing the health risk,  because even chemically non-toxic particles can also penetrate deep into the respiratory tract, and some particles may even reach the pulmonary alveoli.

Fine dust is believed to be cancer-causing, even without having an immediate toxic effect. A great load is placed on the bronchial area and lungs, if the respiratory tracts or the pulmonary alveoli are blocked by fine dust particles. Depending on the application, ultra-fine particles can impact the health of employees and even the product quality.

Harmful ultra-fine particles remain in the air that we breathe for a particularly long time

Particles with a size of 15 µm settle within one minute, unless they are moved by air currents.  Settling can take longer in higher areas. The settling time is 3 minutes for particles with a diameter of 10 µm, and 8 minutes for particles with a diameter of 5 µm. Since settling times do not increase in a linear fashion, particles with a diameter of 1 µm need 4 to 5 hours to settle. Even smaller particles remain suspended and never settle. This means that ultra-fine particles which are particularly harmful to health also remain for the longest period of time in the air, where they can be inhaled.

Coarse dirt harms people and damages machinery

While fine particles remaining  in the air for a particularly long time are a health hazard, coarse particles settle quickly and contaminate surfaces, machine parts and the interior of the machine (if accessible). When the air moves, the particles can be distributed over a wide area and inhaled, which places an additional burden on the respiratory tract.