All masks approved according to EN 140 and certified according to council directive 89/686/EEC. Standard thread connection according to EN 148-1 which allows cost-efficient use of standard screw-filters besides insert filters and reusable holders. The masks can be used as pure filtration device and also as a mask for light airline systems. Two exhalation valves ensure low respiratory resistance. Ergonomic design of the mask bodies and sealing zone as well allow one single size of mask for all faces.