ASZM-TEDA and the Chromium Question in NBC Filter Carbon

In 1992 the US Department of Defense stopped buying chromium-containing impregnated carbon for military gas filters and moved to ASZM-TEDA. The chromium formulation had been in service for roughly fifty years. The US Army’s DEVCOM Chemical Biological Center gives the reason directly: the copper, silver, zinc and molybdenum system is used because “these metals are less toxic and safer for the user than chromium”. The governing specification, MIL-DTL-32101, was established in the late 1980s and from 1992 was the sole testing requirement for the carbon.

If you are specifying CBRN-grade carbon in 2026, the useful thing to know is that the specification has moved since. The current revision is MIL-DTL-32101B, dated 2017, with B w/AMD2 accepted in 2020. A datasheet or tender that cites the 2002 base document — or cites no revision at all — is not citing the current requirement.

The short version

• ASZM-TEDA replaced ASC whetlerite in US DoD service in 1992, after roughly fifty years of chromium-containing carbon, because the replacement metals are less toxic to the user.
• ASC whetlerite’s impregnating solution, per patent US2920050A, was copper 5–9 %, hexavalent chromium 1.5–2.0 % and silver 0.1–0.5 % — solution concentrations, not loadings on carbon.
• The current specification is MIL-DTL-32101B (2017), with B w/AMD2 accepted in 2020. Revision B added live-agent testing and environmental stress testing across tropical, desert and arctic conditions.
• An “aged” sample is conditioned 7 days at 45 °C and 80 % RH before challenge, per the referenced military test protocol — an accelerated proxy for moisture-driven deactivation in storage.
• SURSORB CBRN+ publishes breakthrough minima of >30 min unaged and >28 aged on AC, and >55/>45 on CK, on a chromium-free formulation at BET min 1000 m²/g.

What ASC whetlerite actually was

ASC whetlerite is the chromium-containing predecessor, and the patent record is the cleanest public description of it. US2920050A (“Whetlerite product and process”) specifies an impregnating solution of copper 5–9 %, hexavalent chromium 1.5–2.0 % and silver 0.1–0.5 % as silver nitrate, with ammonia at 8–12 % and carbon dioxide at 5–10 %. Drying runs at 150–175 °C and must stay below 250 °C. The target agents named are hydrogen cyanide, phosgene, cyanogen, arsine and cyanogen chloride.

Those percentages are concentrations in the impregnating solution, not weight percentages on the finished carbon. They are frequently reproduced as carbon loadings. They are not, and we are not going to convert them, because the conversion depends on solution uptake, drying route and carbon density — none of which the patent fixes.

The patent also contains the argument for why the formulation has four ingredients rather than one: copper alone is, in the patent’s words, “not effective for removing arsine and cyanogen chloride” from air at high relative humidity. Each metal is there because a single-metal system failed against a specific agent under a specific condition.

A later patent family — EP0501364A1 and US5192735A, on low-chromium active charcoal — describes standard whetlerisation as roughly 7 wt % copper and 2 wt % Cr(VI), with silver added for arsine and TEDA to extend service life. It calls Cr(VI) “a known carcinogen” and identifies the disposal problem that creates. Its technical contribution is a process change rather than a chemistry change: freeze-drying instead of oven-drying produces smaller, better-distributed crystals, which allowed the chromium content to be halved from 2 % to 1 % at equal performance. That is a useful reminder that in impregnation, where the metal sits usually matters more than how much of it there is.

The specification correction: MIL-DTL-32101B

MIL-DTL-32101’s full title is Carbon, Activated, Impregnated, Copper-Silver-Zinc-Molybdenum-Triethylenediamine (ASZM-TEDA). The base document dates from 2002; the current revision is B, dated 2017, and MIL-DTL-32101B w/AMD2 was accepted in 2020.

DEVCOM’s own account of why revision B happened is worth telling, because it is a procurement story rather than a chemistry story. A single-source supply dependency for this carbon persisted for around three decades. When a second supplier was introduced, the exercise exposed that the specification had effectively been written around one vendor, one mine and one impregnation process — it described that supply chain rather than the performance the filter needed. That is what prompted revision B and the subsequent amendment.

The revised standard incorporates live-agent testing and environmental stress testing across tropical, desert and arctic conditions, measuring, in DEVCOM’s phrasing, “the length of time it takes for agents to break through the carbon” at various bed depths and airflow velocities. Bed depth and velocity are in the test because breakthrough is a system property, not a media property — the same carbon gives different minutes in a different canister.

The test agents and their concentrations

The publicly available agent list and challenge concentrations come from the 3M C2A1 NBC canister technical bulletin, which specifies ASZM-TEDA carbon and cites MIL-DTL-32101:

Test temperature is 24 ± 3 °C. Note that sarin is represented by dimethyl methylphosphonate, a simulant — a physical-properties stand-in for a nerve agent, which is why DMMP appears on commercial datasheets where the live agent obviously cannot.

“Aged” and “unaged”, defined properly

These two words appear on every ASZM-TEDA datasheet and are rarely defined on any of them. In the same 3M bulletin, humidity conditioning is expressed as pre-test and test RH pairs, and an aged sample is one conditioned for 7 days at 45 °C and 80 % relative humidity before the agent challenge.

That is an accelerated storage test, and it exists because impregnated gas-mask carbons lose protective capability through moisture-driven deactivation of the active metal phases during storage and operation. Work published in Security & Future notes that adding TEDA and pyridine derivatives only partially solves that problem. The metals are the reactive part of the system, and water is what degrades them over months in a store, not seconds in a challenge.

Read the two columns together and they tell you something a single number cannot. On our own published data the DMMP figure does not move between unaged and aged, while cyanogen chloride loses ten minutes of margin. The published mechanism for CK removal is reactive rather than purely physical — TEDA’s contribution is documented in the open literature as a synergistic effect with copper(II) — and DTIC’s assessment above is that it is precisely the reactive capacity that is limited and that degrades with environmental exposure. Whatever depends on the metal phase is what a humid store room takes away first. If a datasheet publishes only an unaged column, it is publishing the half of the result that ages best.

The honest framing of what ASZM-TEDA can and cannot do comes from a DoD source. A DTIC report evaluating catalytic materials for military air purification states that fielded filters have limited capacity for agents removed by chemical reaction, offer “minimal protection against several of the toxic industrial chemicals (TICs)”, and degrade with environmental exposure. Chemisorptive capacity is stoichiometric and finite; a filter designed around a defined agent set is not a general-purpose industrial filter; and the shelf clock runs whether or not the filter is used.

That is the context in which an aged breakthrough figure is the more informative of the two numbers on a datasheet.

What Suracsh publishes

SURSORB CBRN+ is our ASZM-TEDA grade: copper, silver, zinc and molybdenum with triethylenediamine on granular coconut-shell carbon, chromium free.

Published breakthrough, in minutes:

SURSORB CBRN+ published breakthrough, unaged and aged. All values are published as minima. The aged condition in the referenced military test protocol is 7 days at 45 °C and 80 % relative humidity before challenge.

Two caveats belong next to that table, and neither of them is in our favour.

First, the datasheet does not name a revision. Its footnote states only that the grade was tested under MIL standard, and asks you to request the full qualification report and the specific test protocol when specifying. The current revision is MIL-DTL-32101B w/AMD2. A figure tested against an earlier revision is not automatically a figure against the current one, and we are not going to imply otherwise on the strength of a footnote that names no edition.

Second, HCl is not on the verified qualification agent list. Hydrogen chloride does not appear in the 3M/MIL agent set above. The >35 and >30 minute HCl figures are Suracsh’s own test results, not results against a standard qualification agent, and should be read that way.

We also publish SURSORB CBRN, a separate impregnated granular grade whose chemistry is not disclosed on the datasheet: BET min 1000 m²/g, apparent density max 0.680 g/mL, moisture max 1 %, ball pan hardness min 85, in sizes 12×30, 12×20, 7×16 and 14×35. Its breakthrough data is available on request rather than published. That is an asymmetry on a site whose whole posture is publishing specifications, and it is worth naming: if you need a published breakthrough table, CBRN+ is the grade that has one.

What we are not going to tell you

Three numbers routinely appear in secondary material about ASZM-TEDA and we will not print any of them, because we could not verify them from a primary source.

• The Cu / Ag / Zn / Mo weight percentages. MIL-DTL-32101B is the controlled source and it is paywalled. No accessible supplier bulletin discloses them.
• The TEDA loading percentage. The commonly quoted range has no accessible primary source behind it.
• HCl as a standard qualification agent. It is not in the verified agent list, as above.

If a supplier quotes you those numbers, ask which document they came from. It is a fair question and it has a short answer or none.

Export control

Everything above is educational and drawn from published patents, a US Army public affairs article, a DoD technical report, a commercial canister bulletin and our own published datasheet. Nothing here is a capability claim beyond the published specification tables, and this article is not a solicitation of defence end users.

SURSORB CBRN+ and SURSORB CBRN are export-controlled grades. Enquiries concerning export-controlled grades require an identified end user and end use before a quotation can be issued. That process is not a formality and it precedes any pricing or sampling discussion.

The full specification for both grades is published in HTML at suracsh.us, and every datasheet downloads without a form or an NDA — including the two above, with their gaps visible. The companion article on what EN 14387 actually tests covers the civilian respirator standard and why breakthrough minutes are not service life.

Sources

• DEVCOM Chemical Biological Center — helping DoD ensure carbon supply
• Army.mil mirror of the DEVCOM article
• MIL-DTL-32101 record, GlobalSpec / NPFC
• MIL-DTL-32101 listing, EverySpec
• MIL-DTL-32101 base document, 2002
• MIL-DTL-32101 Revision B, 2017
• 3M C2A1 NBC canister technical bulletin — agents, concentrations and ageing protocol
• US2920050A — Whetlerite product and process
• EP0501364A1 — Low chromium active charcoal
• US5192735A — Low chromium active charcoal
• Chromium speciation in whetlerite, PubMed
• ASC whetlerite deactivation mechanisms, ScienceDirect
• DTIC ADA433095 — Evaluation of Catalytic Materials for Military Air Purification Applications
• Manoilova, Chatzis & Nickolov, Security & Future 3(1):35–37 (2019)
• Calgon Carbon ASZM-TEDA product bulletin
• Kiani et al., Impregnation on activated carbon for removal of CWAs and radioactive content, ESPR 28:60477 (2021)
• Role of TEDA as an activated carbon impregnant for cyanogen chloride removal — synergy with Cu(II)

Questions