The Myth of Dusty Agent

by Jan Medema

          From time to time a special form of CW agents, liquids adsorbed onto fine dust or liquids absorbed into fine dust, are mentioned as particularly hazardous. Some, mostly self pro-claimed experts, let the general public believe that exposure to agents in this form result in more severe effects than the undiluted liquid agents. An example of such publications is the October 2002 report from Eric Croddy, Senior Research Associate at the Center for Nonproliferation Studies, entitled "Dusty Agent and the Iraqi Chemical Weapon Arsenal." The report, available at http://www.nti.org/e_research/e3_20a.html, comes with an impressive 30 references. However, except for the first one or two news items in Journals and the New York Times, none of these references has anything to do with "Dusty Agents". Neither do the colorful pictures that accompany the article.

          Unfortunately the most important remarks like "Not only do dusty agents increase the amount that can be spread across an area, they can also frustrate and defeat chemical-protection measures" are not referenced and for good reasons. They are absolute nonsense. For the first part, "dusty agent" is at least 50 % non-agent [The Ant-stop mentioned by Croddy contains only 1 % of chlorpyrofos and does not behave as a liquid. Quick sand that behaves as a liquid contains less than 50 % of the liquid]. And in fact, aerosols are more difficult to make and disperse in the atmosphere than liquids or vapors. [NATO Allied Engineering Publication, AEP, 38 Brussels 1993, unclassified version mentions that the challenge from aerosols is 50 % that of vapors.]

          It would be quite a miracle if with 50 % less agent and a weapon containing agent in a form more difficult to disperse, you were able to deliver higher concentrations. For the second part of the sentence, i.e., the frustration and defeat of chemical protection, that also is a myth. Conclusive scientific experiments have shown that "dusty agents" do not frustrate or defeat chemical protection. For instance J. de Ruiter and F. Oeseburg, Testing Protective Clothing with Aerosols, PML-TNO report 1995-C-26. Many other tests have been performed, e.g, the US MIST, in which the deposition of a salt aerosol onto the skin of a man dressed in protective clothing was measured. All showed the same result, the deposition of agent onto the protected skin from a challenge as defined by NATO (AEP 38) is small and would not lead to any agent effects.

          For all "dusty agents", blister or nerve, a few general facts hold:

1. The agent is diluted by a solid; at most 50 % of the payload is real agent (less would not be practical in terms of the energy and weight needed for a weapon).
   
2. The agent does not change its physical characteristics. Due to the forces involved in absorption and adsorption, the vapor pressure might be somewhat smaller than that of the neat agent.
   
3. To my knowledge, no toxicological studies of "dusty agents" have been carried out. Nowhere in the serious literature is an enhanced toxicity mentioned. The famous US report on toxic effects from blister and nerve agents (Reutter/Wade), does not mention any particular toxicity changes for "dusty agents". NATO recently distributed a set of toxic effect levels that also does not mention any particular toxicity for dusty agents.
   
4. Nowhere is a toxicological process described that could explain an enhanced toxicity. There are however changes in exposure. Lower concentration exposures during longer times usually result in less effect.
   
5. "Dusty agents" could form a particular hazard because the fine dust, with agent, is in the form of an aerosol and will penetrate the active carbon filter layers in protective clothing. It is not the amount of agent and dust that penetrates but the amount of agent that is deposited onto the skin that determines the hazard. The "dusty agent" hazard relies on the wind to assist in penetrating the permeable protective clothing.

          During my professional career, I have searched the literature of the past 200 years regarding mustard agent. The first time "dusty mustard" appears is in the eastern desert of Libya (1937/38). Italian chemical officers note that the persistence of mustard was considerably increased when the mustard was mixed with fine desert dust. [Intelligence Report on Italian Chemical Warfare Capabilities. MI 5, London 1943] This is predictable because in the desert, the agent is covered with dust that prevents evaporation and when mustard adsorbs onto a solid, such as the desert dust, the vapor pressure of any adsorbed (or absorbed) agent is slightly lower than that of the neat agent.

          The Italians exchanged this information with their ally of those days, Nazi Germany. The Germans even bought a load of dust from the Italians. [MI 5 report] In 1943 experiments with the mustard loaded dust started in the Kaiser Wilhelm Institute in Berlin. The archives (of the Wehrmacht in Freiburg Germany) did not reveal how the experiments were carried out or whether test animals or humans were exposed to the "dusty agent." (Actually if either exposure took place, it would be the only toxicological study of dusty agent.) In 1944 the experiments were terminated for a remarkable reason. Those who carried out the experiments were dressed in impermeable, rubber-type of suits, and they experienced serious effects around the wrists: erythema and blisters.

          After the defeat of Nazi Germany, the US Army Medical Corps was tasked to interview those involved in chemical and biological warfare. What happens then is unclear, but more than 25 years later, "dusty agent" appears in military reports and later in news articles about the Iraqi CW used against the Kurds again. This time the reports are accompanied by remarks stating with certainty that the "dusty agent" is much more hazardous than the pure compound. [For example, Prof Gosden (UK) mentions the enhanced effects of dusty mustard during a presentations in Shrivenham in 2004, Proceedings 7th CBRN symposium Royal Military College, Shrivenham, UK November 2004] In retrospect it is likely that the analyst who came to this conclusion assumed that impermeable suits provided good protection and that the minute amounts that entered into the protective system must be very potent to cause blistering of the wrists.

          In recent presentations an alternative explanation for the 1944 findings became apparent. Due to the "bellows effect" in all impermeable types of clothing, i.e., the expulsion and entering of air during movement, there is a serious ingress of agent along the wrists and the ankles. Applying extra duct tape improves the protection factor somewhat, but these areas remain vulnerable. In realistic tests with human volunteers, the protection factors noted around the wrists were never above 10 [H. Oudmayer CBDE scientific conference, Edgewood Arsenal, November 2006, Proceedings to be published, a copy of the paper can be requested from the author through Huub.Oudmayer@tno.nl, and J. Medema Fifth SISPAT conference in Singapore, November 2006, proceedings to be published, a copy of the paper can be obtained from dr.ir.janmedema@hetnet.nl] When working with appreciable concentrations of dusty mustard aerosol, it is highly likely that blisters will occur at the wrists because of the ingress of agent and agent contact with sweaty skin. On the other hand, the active carbon based, air permeable suits showed very good protection factors at least 1 if not 2 orders of magnitude better than impermeable suits.

          There are two messages for today's military, and first responders who might be involved in chemical incidents, from my literature analysis and experiments.

1. Do not trust your impermeable suits unless there is a mechanism at hand that cleans the inside air. Even then, the common military active carbon based, air permeable suits may be preferred. These provide protection even when some fools think they can hit you with dusty agent.
2. Do not believe the disaster prophets, they just predict disaster to make some money.