Abstract: A mechanical device is used to estimate a service life of an air filter exposed to a certain chemical at various concentrations, flow rates, and relative humidity conditions. The device includes two members, one of which has at least one window, connected so that their surfaces are movable relative to one another. One member has numerical values for chemical concentrations and service life estimates printed on it. The member having windows has at least one mark printed on it by which it can be oriented relative to the chemical concentration scale on the other member. When the two members are aligned relative to a chemical concentration of interest, the corresponding service life estimate is displayed in an appropriate window.

Abstract: A dust filter bag having a highly porous backing material ply and a method for producing the dust filter bag. The dust filter bag includes at least one filter material ply and at least one backing material ply, the backing material ply possessing an air permeability of at least 900 l/m2 x s, a burst strength of at least 70 kPa, a rupture strength longitudinally better than 10 and transversely better than 3 N, a flexural rigidity longitudinally better than 0.5 cN cm2 and transversely better than 0.25 cN cm2, a basis weight of 30-80 g/m2 and a droplet sink-in time of less than 10 minimum. The dust filter bag can be produced by the following steps: mixing fibers including cellulose fibers and fusible fibers into a homogenous fiber mix, processing the fiber mix into a fiber web by wet laying, drying the fiber web, curing the dried fiber web by thermofusion into a backing material ply, processing the backing material ply with a filter material ply into a raw bag, and finishing the raw bag into a dust filter bag.