Understanding Gas Mask Filters - Which One Is Right For You?

CBRN guide

A gas mask is only half of the system. The MIRA Safety CM-7M page puts it plainly: the mask gives CBRN protection “when used with suitable filters or a breathing apparatus”, and filters are not included.

This guide covers the filters we carry at Civil Safety: how they connect, how to read the rating code, what each one is rated for, and how to store them. Every spec below is taken from our own product pages and written as it appears there. If a page doesn't say something, we don't say it either.

Start with the thread

The MIRA Safety masks covered here, the CM-6M, CM-7M and CM-8M full-face masks and the TAPR half-face respirator, all use 40 mm NATO-threaded filters. The CM-7M page lists that thread as Rd 40 x 1/7" (NATO 40 mm), to the EN 148-1 standard. The CM-6M page is specific: its inhalation chambers are only compatible with the Rd 40 x 1/7" thread in accordance with EN 148-1.

The CM-7M and CM-8M each take up to two filters, and either one can run a single filter on the left or right side. The NBC-77 SOF, NBC-17 SOF and P-CAN are made with standard round threads to STANAG 4155 (EN 148-1), Rd 40 x 1/7". The ParticleMax P3 uses 40 mm x 1/7" NATO threading to EN 148-1:1999.

The VK-700 is sold in two thread versions: EN 148-1 (Rd 40×1/7", order code 1640) and GOST 8762-75 (OZ 40×4 mm, order code 2640). For the EN 148-1 masks above, the EN 148-1 version is the one that matches.

Two more compatibility notes. The NBC-17 SOF is not compatible with the MB-90 PAPR, because of its shorter threads. The TAPR is listed as ideal for three compact filters: the P-CAN Compact, the ParticleMax P3 Compact and the NBC-17 SOF. The MB-90 PAPR moves the filters off your face: it uses two 40 mm CBRN filters on the blower and connects to a standard 40 mm NATO-threaded mask by hose.

How to read the rating code

Each filter carries a rating code made of letters and numbers. The NBC-77 SOF, for example, is rated A2B2E2K2HgSXP3 D R. Our product pages describe the parts of the code like this:

• A: organic vapours. The DotPro 330 lists benzene, toluene and xylene under A2.
• B: inorganic vapours, such as chlorine and hydrogen sulfide (DotPro 330, B2).
• E: acid gases, such as sulfur dioxide and hydrogen chloride (DotPro 330, E2).
• K: ammonia and its derivatives (DotPro 330, K2).
• Hg: mercury vapours (DotPro 330).
• NO and CO: nitrogen oxides and carbon monoxide, both in the VK-700 test table.
• SX: the VK-700 tests this class with phosgene.
• P3: particles. The TAPR page calls P3 the highest particle class, with “reliable protection against solid and liquid aerosols and hazardous microorganisms like bacteria, viruses, spores”.

Read the full code, not just the name. The NBC-77 SOF and NBC-17 SOF are both CBRN filters, but they carry different codes: A2B2E2K2HgSXP3 D R and A2B1E1K1P3 D R. Both pages say the filters are certified by European agencies, carry the CE symbol and comply with EN 14387+A1.

The filters we carry

NBC-77 SOF

The NBC-77 SOF page states that it filters all known CBRN agents, including radioactive iodine. It has a 20-year shelf life and is made to work with a full-face mask, mouthpiece assembly or PAPR. The housing may be black or ranger green, depending on inventory.

NBC-17 SOF

The NBC-17 SOF is sold as the lightweight CBRN filter. It is rated A2B1E1K1P3 D R, has a 10-year shelf life, and works with a full-face mask, mouthpiece assembly, TAPR or PAPR (but not the MB-90).

DotPro 330

The DotPro 330 is intended for industrial hazards and certified to EN 14387:2004+A1:2008. Its page says it “will protect against most CBRN threats”. Listed durations include more than 35 minutes for organic vapours (A2) at 5000 ppm and more than 170 hours for mercury vapours. It weighs 360 g, has a 10-year storage time when factory sealed, and is rated effective from -30°C to +70°C.

VK-700

The VK-700 is a combined filter rated A2B2E2K2HgNOCO20P3. Its page lists organic solvents and acid gases, ammonia and mercury vapours, solid and liquid aerosols, radioactive particles and asbestos fibres, and CBRN agents and tear gas. It weighs 450 g and has a 10-year shelf life when stored between -5°C and +30°C at humidity below 80%.

VK-530

The VK-530 is built for smoke and carbon monoxide and is rated A2B2E2K2HgNO20COP3R. Its page says it helps convert CO into CO2, and that it can be used in environments with as little as 19.5% oxygen. It has a five-year shelf life and should be stored between 2°C (35.6°F) and 55°C (131°F), with humidity lower than 80%.

P-CAN

The P-CAN is designed for law enforcement use against riot control agents, including CS, CN and OC pepper spray. Its page describes up to 12 hours of protection from riot control agents, a 10-year shelf life, a weight of 290 grams (10.2 oz) and a diameter of 111 mm (4.3 inches). It meets EN 14387:2004 + A1:2008 for removing CS/CN gas in vapour form.

ParticleMax P3

The ParticleMax P3 is for biological threats: its page says it is “not suitable for other CBRN threats”. It is P3-certified to EN 143:2000, weighs 100 g, has a 20-year shelf life and comes in a pack of six.

Match the filter to the job

• Broad CBRN: NBC-77 SOF, or the lightweight NBC-17 SOF (not for the MB-90 PAPR).
• Smoke and carbon monoxide: VK-530. The VK-700 page describes it as broader protection than the VK-530.
• Industrial chemicals and mercury vapours: DotPro 330 or VK-700.
• Riot control agents: P-CAN.
• Viruses and bacteria only: ParticleMax P3.

The ParticleMax page also recommends keeping a variety of filters on hand.

Storage and handling

The NBC-17 SOF page sets out clear storage rules. Keep filters unopened in the manufacturer's sealed bag, in a clean place at an even temperature, ideally -5 to +30°C with relative humidity below 80%. The storage period is marked on the filter label. Don't try to regenerate filters, and never clean them with compressed air or compressed water.

The VK-530 page adds: keep filters away from significant vibration, solar radiation and shocks, and out of contact with ketones, esters, hydrocarbons, acids and strong bases. After use, filters are special refuse: dispose of them according to what they filtered and your local waste regulations.

Before you buy

Check three things: the thread matches your mask, the rating code covers the hazard you're planning for, and the shelf life suits how long the filter will sit in storage. The label and instructions that come with your filter always take priority over this summary.

Browse the full range in Gas Mask Filters, find a compatible mask in Gas Masks, or see suits and PAPR in CBRN Gear.