Particulate | P1 Low efficiency P2 Medium efficiency P3 High efficiency | White |
Organic gases with boiling points >65°C as specified by manufacturer | A1, A2, A3* | Brown |
Inorganic gases and vapours as specified by manufacturer, excluding carbon monoxide | B1, B2, B3* | Grey |
Sulphur dioxide and other acid gases and vapours as specified by manufacturer | E1, E2, E3* | Yellow |
Ammonia and organic ammonia derivatives as specified by manufacturer | K1, K2, K3* | Green |
Mercury | Must incorporate a P3 filter | Red–white |
Oxides of nitrogen | NO must incorporate a P3 filter, single use only | Blue–white |
Organic gases with boiling points <65°C as specified by manufacturer | AX | Brown |
Filters against specific substances as specified by manufacturer | SX, marked with name of chemical | Violet |