The Evolution Powered Respiratory protection system is a lightweight and ergonomic solution able to work efficiently in very dusty environments. How long filter cartridges last is down to the level of contamination in a particular working environment. Whenever possible check the airflow of the unit prior to use. To fit new filters align the fittings on the filter with those on the filter housing, push fit and tighten. Supplied as a pair, these filters feature a high capacity pleated filter cartridge giving TH1P protection. The high efficiency sub-micron particulate filters have a high impact polystyrene front and back.