STANAG 4155 CBRN mask and canister screw thread agreement

What it is

STANAG 4155 is a NATO Standardization Agreement, currently Edition 2, promulgated 6 February 2019. It is not a technical specification. It is the agreement by which NATO nations commit to implement AEP-4155, Edition A, the Allied Engineering Publication that sets out the screw thread dimensions for CBRN protective masks and filter canisters. The document's own aim is to respond to an interoperability requirement: "to provide for full mechanical interchangeability between CBRN protective masks and filter canisters for NATO forces irrespective of national origin of masks and canisters" - so a filter canister made in one nation screws onto a mask made in another. Read on its own, STANAG 4155 requires nothing of a mask or filter canister manufacturer. Its obligations run to nations and to NATO bodies, and the thread dimensions themselves sit in AEP-4155, not in this cover.

Who it binds, and how

STANAG 4155 is explicit that it binds nations rather than organisations. Its letter of promulgation describes the enclosed agreement as one "which has been ratified by member nations, as reflected in the NATO Standardization Document Database (NSDD), is promulgated herewith." Under "Agreement," participating nations agree to implement AEP-4155, Edition A - a national commitment, made by ratification, not a duty a supplier signs up to by reading this document. Ratification and implementation stay separate steps: nations that have not already done so are invited to "examine their ratification of the STANAG and, if they have not already done so, advise the NSO of their intention regarding its implementation." So "is STANAG 4155 mandatory" has no single answer: it depends on whether a given nation has ratified and implemented it, and this cover names no manufacturer, supplier or test house at all.

What the agreement commits nations to

The STANAG states it "is effective upon receipt and ready to be used by the implementing nations and NATO bodies" - a NATO-wide mechanism, with partner nations separately "invited to adopt this STANAG." It is considered implemented once nations "have equipped the forces with CBRN protective masks and filter canisters with rolled threads conforming to AEP-4155; and by incorporating the provisions of this AEP into their national procurement specification." Nations are invited to "report on their effective implementation of the STANAG in accordance with AAP-03," and partner nations to report their adoption the same way.

The RD 40 mm thread, and the alternative-connector carve-out

The agreement states: "It is agreed within NATO, to retain the ability to use an RD 40 mm threaded canister in extremis on all negative pressure air purifying devices." It also records that "NATO recognizes alternative connectors (e.g. bayonet joints) between the mask and the canister have been developed and can be used alternatively." A nation that fields an alternative connector must still "equip at least the mask with the ability to convert the joint into an RD 40 x 3.63 mm (female) thread," a conversion the document says "needs to be performable." Once converted, "the requirements regarding tightness and protection factor according to AEP-71 and AEP-73 are to be achievable." Beyond that fallback dimension, STANAG 4155 prints no thread table of its own: the full geometry and tolerances sit in AEP-4155.

A cover agreement, not the thread specification itself

A reader who only has STANAG 4155 in hand does not yet have the thread dimensions it points to. Those sit in AEP-4155, Edition A, the publication named under "Standard." The STANAG also names STANREC 4727 (covering AEP-73, on protective mask operational characteristics and evaluation), STANREC 4725 (covering AEP-71, on fit and protection testing for negative-pressure respirators), and STANREC 4548 (covering AEP-38, on CBRN protective clothing), plus two civil standards outside our catalogue: EN 148-1 and ISO 17420-3, both on respiratory-device thread connections. Edition 2, 6 February 2019, supersedes an earlier edition of STANAG 4155 (the source text names the prior document but prints no edition number for it).

Reporting and review

National responses on ratification and implementation are recorded in the NATO Standardization Document Database. The STANAG itself "is to be reviewed at least once every five years," with the result recorded in the NSDD, and "nations and NATO bodies may propose changes, at any time, through a standardization proposal to the tasking authority (TA)." The agreement is supervised under CNAD, AC/225 NAAG (the NATO Army Armaments Group) and JCBRND CDG (the Joint CBRN Defence Capability Development Group), with Germany named as custodian through Bundeswehr research into protective technologies.

What it does not cover

STANAG 4155 names no thread dimension or tolerance table beyond the RD 40 mm fallback and its RD 40 x 3.63 mm (female) conversion requirement - the full specification sits in AEP-4155, which this agreement covers but does not reproduce. It also names no test method for tightness or protection factor: those sit in AEP-71 and AEP-73. And it names no assessment or certification scheme: the only stated check is that the STANAG itself is reviewed periodically, not that a nation, an organisation or a piece of equipment is certified.

Standards it references

• STANREC 4727Background
• AEP-73Background
• STANREC 4725Background
• AEP-71Background
• STANREC 4548Background
• AEP-38Background