The maximum admissible residual dust content contained in the clean gas is indicated in TA-Air; inorganic dusts are divided in three special categories because of their toxicity.
Bag filters can have a residual dust content of 7 mg/m3 at most. The seams of the individual bags are a weak point as regards bag filtering. When these seams are agglutinated with polyester felt a value of 2 mg/m3 can be realised.
The residual dust content of a cartridge filter that can be achieved amounts to some 2 mg/m3.