This standard specifies the minimum requirements for gas filters & combined filters for use as part of a respiratory protective device. Gas filters remove specified gases and vapours. Combined filters remove solid and/ or liquid particles, and specified gases and vapours. According to their application and protection capacity gas and combined filters are classified in types and classes .

Types of filters

 Gas filters are classified according to the type of specified gas they remove :

• Type A:  For use against certain organic gases and vapours with a boiling point higher than 65?C, as specified by the manufacturer. Type A filters are required to be marked with the colour code Brown

• Type B: For use against certain inorganic gases and vapours as specified by the manufacturer (excluding CO). Type B filters are required to be marked with the colour code Grey.

• Type E:  For use against sulphur dioxide and other acidic gases and vapours as specified by the manufacturer. Type E filters are required to be marked with the colour code Yellow .

• Type K: For use against ammonia and organic ammonia derivatives as specified by the manufacturer. Type K filters, are required to be marked with the colour code Green .

Type A,B,E & K filters are further classified according to the filter capacity :

• Class 1 - low capacity , up to 1000ppm

• Class 2 - medium capacity, up to 5000ppm

• Class 3 - high capacity, up to 10,000ppm