Filter or air? Specifying respiratory protection

A filter cannot make oxygen. How to choose between filtering respirators and air-supplied apparatus, and what to state so the filter matches the hazard.

Every respiratory selection starts with one question, and it is not which mask. It is whether the air in the space can be cleaned, or whether it has to be replaced.

A filter removes contaminants from the air passing through it. It cannot add oxygen. In an oxygen-deficient atmosphere a filtering respirator does nothing useful and gives the wearer a strong impression that they are protected. That is the single most dangerous misunderstanding in this category, and it is why escape hoods certified to EN 403 carry an explicit limit: they are not for use where oxygen may fall below 17% by volume. Where the atmosphere is deficient, unknown, or immediately dangerous, the answer is air-supplied — self-contained breathing apparatus to EN 137, or an airline system.

Everything below assumes the atmosphere can be filtered.

Step one: the substance, by name

A filter is specific. Under EN 14387, gas filters carry a letter for the hazard family:

Letter	Against
A	Certain organic gases and vapours with a boiling point above 65 °C
B	Certain inorganic gases and vapours
E	Sulphur dioxide and other acid gases and vapours
K	Ammonia and organic ammonia derivatives (amines)

Type A is colour-coded brown and type B grey. Specific filters also exist for mercury vapour and carbon monoxide. Alongside the letter, a class number from 1 to 3 indicates capacity — low, medium, high.

Particulate filters are graded separately under EN 143: P1 stops at least 80% of aerosol, P2 at least 94% and P3 at least 99.95%. Combined filters carry both a letter and a P grade, because many real atmospheres contain both a gas and a particulate.

None of this can be selected from the word "fumes". It needs the substance and its concentration.

Step two: the facepiece

The facepiece decides how well the filtered air is kept separate from the unfiltered air, and how much of the face is protected.

Disposable filtering facepieces are covered by EN 149 and graded FFP1, FFP2 and FFP3, filtering at least 80%, 94% and 99% of airborne particles respectively. They protect against particulates. Where a US specification applies, N95 is not a synonym — it is an approval class under 42 CFR Part 84, requiring at least 95% capture of a charge-neutralised sodium chloride aerosol at 85 litres per minute. The two are close in filtration and different on a certificate, which matters when an auditor is checking.

Reusable half masks to EN 140 are carriers. What they protect against is decided entirely by the filter fitted, which is a separate line on the purchase order and a separate decision. Two failures follow from forgetting that: masks bought with no filter budget, and particulate filters fitted where a gas filter was needed.

Full-face respirators to EN 136 add eye protection and a larger sealing surface. If the contaminant irritates eyes, this is not an upgrade, it is the requirement.

Step three: the seal

None of the above works without a seal against skin. A facial-hair policy is part of a respiratory programme, not an HR preference — a sealed facepiece cannot seal over a beard, at any grade. Where that is not workable, the selection moves to a hood or a powered system that does not rely on a face seal.

Fit testing is what converts a specification into protection. Two people issued the same mask in the same size do not necessarily achieve the same fit.

Escape is a separate purchase

Escape devices are not working respirators and cannot be used as one. EN 403 covers filtering hoods for escape from fire, protecting against combustion particulates, carbon monoxide and other toxic gases, and defines two classes: M for a device carried on the person and S for one that is stored. EN 1146 covers compressed-air escape apparatus, which is what the oxygen-deficiency case requires.

An escape device is judged on how fast someone who has never worn one can don it under stress. That argues for hoods over sealed masks, and for training units so drills do not consume live devices.

What to state in an enquiry

The substances present, by name, and their concentrations.
Whether oxygen deficiency is possible — this decides filter against air.
Whether particulates are present as well as gases.
Duration of wear per shift.
Whether eyes are irritated by the contaminant.
Working or escape duty.
Existing mask models on site, so filter fittings match — bayonet and threaded connections do not interchange, and neither do most proprietary fittings.
Fit testing and facial-hair policy.
Consumption rate for disposables and filters.
Storage conditions — sealed filter packaging and shelf life matter in Gulf heat and humidity.

Sources

Standards evolve. Verify the current edition and the exact requirement against the standard itself or your client's specification before relying on it.