Protect against the following gases/vapours: Type A protects against organic gases and vapours, such as solvents, with boiling points > +65 °C. Type B protects against inorganic gases and vapours, such as chlorine, hydrogen sulphide and hydrogen cyanide. Type E protects against acidic gases and vapours, such as sulphur dioxide and hydrogen fluoride. The SR 500/SR 500 EX fan unit must always be used with two particle filters or two combined filters consisting of gas filters and particle filters.