Respiratory protective filters: colour code, class, etc.

There are different types of facepieces (half mask, full face mask, mouthpiece, hood, helmet, etc.) and different types of filters (gas filters, particle filters, combined filters).


You can quickly feel overwhelmed by the wide range of references and brands on the market! And yet, choosing the right filter is just as important as selecting the right respiratory protective equipment. Read on for an overview of all the filters available, their colour code, efficiency class, and so on.


Cartouche filtrante

Why are filters such an important part of respiratory protection?

Four European standards have been put in place. They define the respiratory protective filters to be used in each case: (please refer to Standards & regulations for respirators)

  •     NF EN 14387:  Gas filter(s) and combined filter(s)
  •     NF EN 143: Particle filters (new legislation, P1, 2, 3: R = reusable dust filters, NR = non-reusable dust filters 2009)
  •     NF EN 372: Respiratory protective devices. Sx gas filters and combined filters against specific named compounds 14387
  •     EN 149: Disposable masks

There are 3 types of filters (gas filters, aerosol filters and combined filters), providing protection against two types of toxic contaminants:

  •     Aerosols: dust, particles, fibres, fumes, micro-organisms such as viruses and bacteria
  •     Gaseous substances: gas and vapours
Did you know?

Did you know?

An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas, with a falling speed of less than 0.25m/s. In the air, in normal conditions, that corresponds to particles with dimensions of less than 100µm.

Gas filters

Gas filters provide protection against vapours, chemical substances and toxic gases. They usually consist of a bed of activated carbon. They are described according to 2 criteria: filter type and class.

> How are the various types of gas filter defined?

A specific filter for a given gas or family of gases or vapours is indicated through marking consisting of a letter and a strip of a certain colour. If the filter is designed to protect against several families of gas simultaneously, we call it a combined filter: it is designated by the juxtaposition of a letter and the corresponding colour strips (page 108 of the catalogue).

For example:

AB = Filters organic gases/vapours and inorganic gases/vapours
BK = Filters inorganic vapours, ammonia and ammonia derivatives

> How to select the right class of efficiency for your gas filter

As for aerosol filters, there are three classes of protective filters based on their capacity (in other words, the best balance between volume and effectiveness of the absorbent material):

  •     Class 1: For gas concentrations of less than 0.1% by volume, the lowest capacity (filters for half masks) – e.g.: A1
  •     Class 2: For gas concentrations of between 0.1% and 0.5% by volume, medium capacity (cartridge) – e.g. ABEK2
  •     Class 3: For gas concentrations of between 0.5% and 1% by volume, the largest capacity (large-capacity canister worn at waist-level)

At an equivalent ambient concentration level, a class 3 filter will operate for longer than either a class 2 or a class 1 filter.

> Some examples:

     A: xylene, styrene, phenol, white spirit, etc.
     B: SO₂, H₂S, Cl₂, etc.
     E: ntiric acid, etc.
     K: ammonia derivatives
     AX: acetone, butane, methanol, etc.

Note: Some manufacturers offer specific filters that provide protection against carbon monoxide (CO). They are to be used exclusively with life-saving and evacuation devices.

Gas filter colour codes

> How long is a gas filter effective for?

A gas filter no longer functions properly when the carbon granules become saturated. It starts to let through all the pollutants with which it is in contact. For this reason, a gas filter needs to be replaced on a regular basis, before the filter becomes totally saturated.

It is important to know the minimum breakthrough time required by the NF EN 14387 +A1 standard:

Table showing minimum breakthrough times

Aerosol and particle filters

Particle filters provide protection against dust, fumes, micro-organisms and viruses.

> How to recognise a particle filter

Particle filters are identified by their characteristics, which are printed directly on the mask. FF stands for Filtering Facepiece, while P1, P2 and P3 refer to the class of filter efficiency. On filtering cartridges, this information is shown on a white strip marked either P1, P2 or P3.

> How to select the right class of efficiency for your particle filter

The different particle filter classes:

  •     Class 1 (P1) Least filtering
        Filters at least 80% of airborne particles (means that fewer than 20% of particles pass through the filter)
        Offers protection against solid particles that are not specifically toxic (calcium carbonate, etc.)
  •     Classe 2 (P2) Intermediate efficiency
        Filters at least 94% of airborne particles (means that fewer than 6% of particles pass through the filter)
        Offers protection against hazardous and irritant airborne particles in solid and/or liquid form (silica, sodium carbonate, etc.)
  •     Class 3 (P3) High level of efficiency
        Filters at least 99.95% of airborne particles (means that fewer than 0.05% of particles pass through the filter)
        Offers protection against toxic airborne particles in solid and/or liquid form (beryllium, nickel, uranium, etc.)

> How long is a particle filter effective for?

The service life of particle filters depends on the environment. The filters become clogged over time and let less and less air through. When it becomes difficult to breathe, you will know the filter is getting to the end of its service life and needs to be replaced.

Combined filters

> How to protect yourself against airborne particulate, gases and vapours, all at the same time

Combined filters are designed to offer protection against airborne particulate, gases and vapours simultaneously. They are made up of a particle filter combined with a gas filter. They are characterised by dual marking: the coloured strip for gas filters plus the white strip for particle filters.

Example: A2B2P3 filter

A filter with the colour code shown opposite is suitable for the following contaminants:
A: Gas and vapours of organic compounds with a boiling point ≥ 65°C, up to the concentrations covered by a class 2 filter (5,000ppm)
B: Inorganic gases and vapours up to the concentrations covered by a class 2 filter (5,000ppm)
P: Particles up to the concentrations covered by a class 3 filter