Dust categories are crucial. They indicate the suitability of any given dust and the specified maximum allowable concentrations (MAC). And they define the corresponding filter system's required degree of filtration.
Dust class L: Non-hazardous, harmless dusts such as house dust, plaster and lime. MAC > 1 mg/m³, filter system degree of filtration > 99%
Dust class M: Harmful dusts such as cement, filler, renders, paints and varnishes. MAC > 0.1 mg/m³, filter system degree of filtration > 99.9%
Dust category H: Pathogenic dusts that are carcinogenic (such as asbestos, arsenic and lead) or are contaminated with bacteria, germs or mould. MAC > 0.1 mg/m³, filter system degree of filtration > 99.995%