Gas Mask Filters: Colour Codes and Service Life

Why do gas mask filter colours matter?

Imagine an operator working on a solvent filling line in a chemical plant being given a mask with a grey filter. The mask fits the face perfectly and the operator thinks they are protected; but a grey (B) filter is not designed to trap organic vapour. That is why gas mask filter colours are not a labelling detail but the first sign of whether there is any protection at all.

Gas and vapour filters are marked with a letter, a colour and a class number under the TS EN 14387 standard. The letter and colour show which group of gases the filter traps, and the class number shows how much it can hold. Respiratory protective equipment protecting against harmful substances is in the highest risk category (Category III) under the Regulation on Personal Protective Equipment (2016/425/EU).

On the workplace use side, the Regulation on the Use of PPE in Workplaces applies: the employer determines PPE according to the results of the risk assessment and assesses its suitability before choosing it (Art. 7), has it maintained and replaced according to the manufacturer’s user manual, provides hands-on training and ensures that instructions are understandable to employees (Art. 6). For the general selection process, see our article on how to choose PPE.

A, B, E, K filters: colour code table

Filter type	Colour	Protects against	Typical use
A	Brown	Organic gases and vapours with a boiling point above 65 °C	Thinners, toluene, xylene, styrene
AX	Brown	Organic compounds with a boiling point of 65 °C and below, on the manufacturer’s list	Some low-boiling solvents
B	Grey	Inorganic gases and vapours (excluding carbon monoxide)	Chlorine, hydrogen sulphide
E	Yellow	Sulphur dioxide, hydrogen chloride and other acid gases	Acid baths, acid filling
K	Green	Ammonia and organic ammonia derivatives	Ammonia refrigeration maintenance
Hg-P3	Red-white	Mercury vapour	Equipment containing mercury
NO-P3	Blue-white	Nitrogen oxides	Certain welding and acid processes
P1, P2, P3	White	Dust, fumes and mist (particulates)	Spray mist, dust

The class number shows the filter’s capacity: class 1 is low (up to 1,000 ppm, i.e. 0.1% by volume), class 2 medium (up to 5,000 ppm) and class 3 high capacity (up to 10,000 ppm). These values are the upper limit of the filter’s capacity; they do not mean it is safe to work at that concentration. The highest concentration that can be used is also limited by how well the mask fits the face.

Combined filters carry more than one letter. “ABEK1” is a low-capacity filter against four gas groups. “A2P2” traps both organic vapour and particulates; in spray painting, solvent vapour and paint mist are present together, so this kind of combination is needed. No ABEK filter traps carbon monoxide; a separate solution is needed where there is a CO risk.

Choosing by chemical: four steps

Look at the SDS. Section 8 of the safety data sheet (exposure controls and personal protection) often states the recommended filter type. If it does not, the boiling point in section 9 determines the choice between A and AX for organic vapours. For reading the form, see our article on how to read a safety data sheet.
Measure the concentration. The filter class and mask type are chosen according to the measurement result. We plan measurements with authorised laboratories; if the result exceeds the limits of a filter mask, you move to the supplied-air option in the fourth section.
Check whether there are particulates. If mist forms along with spraying, grinding or evaporation, choose a combined filter with P added to the gas filter. If there is only dust, no gas filter is needed; in that case, our article on FFP1, FFP2 and FFP3 dust masks gives guidance.
Choose the mask to fit the face. A half mask (TS EN 140) covers the mouth and nose; a full face mask (TS EN 136) also covers the eyes. For substances that irritate the eyes, such as ammonia, chlorine and acid gases, a full face mask is preferred. The mask size is chosen to fit the employee’s face and the seal is checked every time it is put on; a beard causes leakage at the edge of the mask.

Common matches in chemical and plastics businesses: an A-type organic vapour filter for lamination with polyester resin and styrene; A2P2 for solvent-based spray painting; a full face mask with a K filter for planned maintenance of an ammonia refrigeration system; an E filter for acid filling. Responding to an ammonia leak, however, is not a job to be done with a filter mask; we explained this distinction in our article on ammonia refrigeration systems.

Filter replacement intervals: do not wait until you smell it

A gas filter protects until the capacity of the activated carbon inside it to trap gas is full. When it is saturated, gas starts to pass through the filter, and this usually goes unnoticed. The filter replacement interval is determined by these factors:

Concentration: The denser the gas in the environment, the faster the filter fills up.
Humidity: In humid air, the capacity of organic vapour filters falls.
Temperature and breathing rate: A person doing heavy work breathes more air; the filter is used up faster.
Mixtures: Several vapours can displace one another in the filter.
Filter class: Class 2 lasts longer than class 1 in the same conditions.

A workable replacement arrangement is set up as follows:

Use the manufacturer’s service life calculation tool or tables with the measured concentration, humidity and workload.
Shorten the calculated time with a safety margin and turn it into a rule that can be applied on site, such as “at the end of every shift” or “every 4 hours of use”.
Record replacements: date, filter type and class, lot number, user, hours of use and reason for replacement.
For particulate filters, replace them without waiting for the interval when breathing becomes difficult, the filter gets wet or is damaged.
For some filters, the manufacturer limits use further. The standard provides for a maximum of 50 hours of use for Hg-P3 filters; NO-P3 filters are single-use; a single-use requirement is also common for AX filters. Follow the instructions on the packaging.

The expiry date of an unopened filter is printed on it. A filter whose packaging has been opened continues to trap vapours in the environment even when not in use; store the mask in a closed box or bag, do not leave it out. To organise handover and replacement records, see our article on PPE handover and replacement tracking.

When is a supplied-air device needed?

A filter mask cleans the ambient air; if there is not enough oxygen in the air, it gives no protection. In the following situations, instead of a filter mask, a device that supplies the employee with clean air from outside (an airline respirator or self-contained breathing apparatus) is used:

Possible oxygen deficiency: Confined spaces such as tanks, silos, wells and pits. For oxygen values and the order of measurement, see our article on gas testing in confined spaces.
Unknown substance or concentration: In a leak of an unknown substance, it is not possible to choose the right filter.
Concentrations exceeding the filter class or the mask’s protection limit.
Gases with no suitable filter: Such as carbon monoxide.
Leak response and rescue: For the equipment of teams responding to chemical leaks, see our article on chemical spill response.

Powered air-purifying respirators make breathing easier but are still filter devices; they are not used in oxygen deficiency. The other requirements for confined space work are explained in our article on working in confined spaces.

Maintenance, storage and training

Personal use: Do not use the mask as shared equipment passed between shifts; hygiene and facial fit suffer.
Cleaning after use: The mask body is cleaned using the method recommended by the manufacturer, and the filter is removed and stored in a closed place.
Check before putting it on: Valves and seals, straps and cracks in the body are checked. Defective PPE is not used until the defect is rectified (Regulation on the Use of PPE Art. 8/3).
Hands-on training: The employee learns in practice how to put the mask on, check the seal, change the filter and read the colour codes. A simple board showing the filter type can be posted next to the filling station.

In our OHS specialist service, we choose respiratory protection according to your chemical inventory, measurement results and the nature of the work, and link the replacement schedule and training to it. Other sector-specific risks are on our chemicals and plastics page. We explained in our article on carcinogens and mutagens that protective equipment is only the last resort in areas where carcinogens are handled.

Frequently Asked Questions

Does an ABEK filter protect against every gas?

No. An ABEK filter protects against organic vapours, inorganic gases, acid gases and ammonia; carbon monoxide, some low-boiling organic substances and particulates are not covered. If particulates are also present, a combined filter with P is needed.

When is a gas mask filter replaced?

Not according to smell, but according to a calculated replacement schedule. Assess the concentration, humidity, workload and filter class with the manufacturer’s calculation tool, shorten the time with a safety margin, turn it into a written rule and record every replacement.

Does a dust mask protect against organic vapour?

No. FFP-class dust masks trap particulates; they give no protection against thinner or solvent vapour. If there is vapour, an A-type gas filter is used, and if there is mist along with the vapour, an A and P combination.

Can an employee with a beard use a half mask?

A beard causes leakage at the edge of the mask in contact with the face and seriously reduces protection. In work requiring respiratory protection, either the contact area is kept clean-shaven or a hooded device that does not depend on facial fit is considered.