Respirator Filter Colours and Classes - Which One Fits?
The coloured bands on a respirator filter are no accident - to EN 14387 they encode which gases or vapours the filter protects against. This guide explains the colour codes A, B, E and K, the gas filter classes 1 to 3 and the particle stages P1 to P3, and shows when each filter fits.
View respirator filtersWhat do the colours A, B, E and K mean?
To EN 14387 every gas filter carries a coloured band and a letter that define its use. The four most common types are A (brown) against organic vapours with a boiling point above 65 °C, B (grey) against inorganic gases such as chlorine or hydrogen sulphide, E (yellow) against sulphur dioxide and acid gases, and K (green) against ammonia and organic amine derivatives.
Beyond these basics there are special filters: AX for organic vapours below 65 °C boiling point, SX for named single compounds, Hg-P3 (red-white) against mercury vapour and NO-P3 (blue-white) against nitrous gases. Combination filters carry several bands, so an ABEK filter shows all four letters.
What do gas filter classes 1, 2 and 3 mean?
The number after the letter describes capacity - how much gas the filter can bind before breakthrough. It does not signal a higher level of protection, but the maximum gas concentration allowed at the workplace.
- Class 1 (low): up to 0.1 vol.% (1000 ppm) gas concentration - light exposure.
- Class 2 (medium): up to 0.5 vol.% (5000 ppm) - typical industrial use.
- Class 3 (high): up to 1.0 vol.% (10000 ppm) - high concentrations, usually full-face mask.
So an A2 filter suits medium solvent concentrations, an A1 only low ones. A higher class means more activated carbon, more weight and higher breathing resistance - which is why you match the class to the concentration rather than always picking the largest.
What do particle stages P1, P2 and P3 deliver?
Particle filters to EN 143 capture dusts, aerosols, fume and mist and are graded into three efficiencies. The higher the number, the finer the separation and the lower the permitted penetration.
For hazards that appear as both gas and particle - for example when painting or spraying - you combine gas and particle filters, such as A2-P3. The suffix R marks reusable particle filters, NR single-use ones.
Frequently asked questions
What does the colour on a respirator filter mean?
To EN 14387 the colour encodes the substance group: brown (A) for organic vapours, grey (B) for inorganic gases, yellow (E) for acid gases and green (K) for ammonia. Combination filters show several bands.
Is a class 3 filter always better than class 1?
No. The class only indicates the maximum allowed gas concentration, not a better filtering effect. Class 3 holds more activated carbon and has higher breathing resistance - for low concentrations class 1 or 2 is enough.
When do I need a combination filter such as A2-P3?
Whenever gases or vapours and particles occur together, for example when painting, spraying or welding. The gas section binds the vapours, the P3 section the aerosols and fine dust.
Does a gas filter protect in low oxygen?
No. Filtering devices require at least 17 vol.% oxygen and a known contaminant. In confined spaces, tanks or unknown atmospheres a self-contained supplied-air device is mandatory.
Looking for the right respirator filter?
We supply gas, particle and combination filters to EN 14387 and EN 143 - matched to half and full-face masks from leading makers.
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