NOVELTY - Dry purification of air loaded with harmful materials and dust in animal stalls, by passing the air through subdivided sections of the stalls, circulating through a filter, redividing and blowing into the sections, is carried out with hemp filter(s), operating in a suction stream, consisting of light, non-steeped, randomly packed, binder-free fibers and additives. The loading with harmful materials is continuously monitored by measuring the pressure loss at the filter inlet and outlet.    USE - Especially in plants for rearing animals such as pigs or cattle (claimed). The process removes air components with the potential to cause reduced growth and/or lung diseases in the animals, such as harmful gases (e.g. carbon dioxide, ammonia, methane, phenol-indole and hydrogen sulfide), dust, bacteria and their decomposition products, viruses, fungi, allergens (e.g. pollen) and metabolites.    ADVANTAGE - The purification system is effective (typically reducing dust by up to 75% and overall germ counts by up to 80%) and environmentally friendly; has low operating costs; and requires simple apparatus and little maintenance. Water vapor condensing in and on the hemp fibers is bonded in the fibers and acts as binder, so that no added binder is required. The dry process simplifies construction of the plant, since no water processing units are required. The system is easily adapted to particular stalls, and the filter is easy to introduce in cassette form.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for corresponding purification apparatus, where the stall is divided into several sections for suction of impure air and blowing of purified air, containing flow-connected suction, transport and blowing channels. Each section has several boxes and ventilator(s) for supplying the impure air to a filter for removing harmful materials and blow the purified air (after division) into the individual sections. The novel feature is that the filter consists of a filter unit (4) containing hemp packing as above, located in cassette(s) with flow connections to the suction, transport and blowing channels (2, 3, 5), a differential pressure meter being provided at the air inlet and outlet sides to assess the loading of the filter with harmful materials.    DESCRIPTION OF DRAWING(S) - The figure shows a plan view of a stall plant provided with the air purifying apparatus.    Stall plant (1)    Suction channel (2)    Blowing channel (3)    Filter unit (4)    Transporting channel (5)    Inlet and outlet side openings of blowing channel (6, 12)    Pig boxes (8)    Inlet and outlet side opening of suction channel (9, 17)    Shaped suction piece (10)    Shaped blowing piece (11)    Piece of tubing (16)    Inlet side opening of transporting channel (18)    Longitudinal sides of stall plant (L1, L2)    Sections (S1, S2)