The great diversity of substances makes the selection of good protection quite difficult. Even more: an incorrect choice may have fatal consequences. Therefore, it is imperative to make an educated and correct choice.
Protection against solid particles
Filtering substances is done, for instance, by means of electrostatically charged fibres in a filter cloth. The dust particles that are sucked into the mask, as a result of breathing, will be attracted by those fibres and remain attached to them. The clean, filtered air will go through the mask and is subsequently breathed in. When the filter is full, you will find that breathing through the filter becomes more difficult.
Protection against gases and vapours
Filtering of gases and vapours is done in a totally different way. A cassette, that can be attached to the mask, contains active coal. The polluted air that is being breathed in, will be sucked through this active coal. The molecules of the hazardous fumes will attach to the coal, after which the clean air is being breathed in. When the filter is full, the molecules will be breathed in. Thus, gas- or vapour filters have but a limited capacity.
There are also filters available that protect against both risks.