GA is a colorless to brown (depending on purity) liquid organophosphate nerve agent with an intermediate persistence (evaporation rate about 1/20th of water). It has a faintly fruity odor (which is absent for the pure material).

CHEMICAL AND PHYSICAL PROPERTIES

Structural Formula

DETECTION

Nerve agent sensitive chemical agent detectors (e.g., CAM, M18A2, M256, etc.) and papers (e.g., M8, M9) may be used for detection.

The presence of the dimethylamine and cyanide groups on the phosphorus make this agent easy to distinguish from other nerve agents using NMR.

SYMPTOMS AND EFFECTS

Lowered acetylcholinesterase levels are indicators of nerve agent intoxication in victims.

Depending on the degree of intoxication, symptoms may include:

Onset is usually rapid, occurring within minutes of exposure.

MEDICAL COUNTERMEASURES

Remove casualties from exposure as rapidly as possible. Casualties must not be moved into clean treatment areas where unmasked/ungloved personnel are working until decontamination is complete.

Medical treatment should include decontamination of casualties at as early a stage as possible. See the section DECONTAMINATION.

Medical personnel treating casualties should avoid direct (skin-to skin) contact; protective gear including breathing protection should be worn when treating casualties prior to decontamination. Latex gloves are not adequate protection. Chemical protective (butyl rubber) gloves must be worn.

The immediate treatment for nerve agent intoxication is intravenous injection of 2 mg atropine sulfate (intramuscular injection should be considered if the patient is hypoxic and ventilation can not be initiated, as there is a risk of ventricular fibrillation). This should be followed by additional injections of atropine at 10-15 minute intervals, continuing until bradycardia has been reversed (e.g., until the heart rate is at 90 beats/minute). If breathing has stopped, a mechanical respirator should be used to ventilate the patient. While exhaled air is not ordinarily a hazard, DO NOT ATTEMPT MOUTH-TO-MOUTH RESUCITATION without proper shields owing to the possible presence of residual agent on the face. If possible, oxygen or oxygen-enriched air should be used for ventilation. If possible, monitor cardiac activity.

Pralidoxime salts are somewhat ineffective in restoring acetylcholinesterase activity after exposure to tabun; however, they do not interfere with treatment, and so there is no reason to refrain from their use if the agent is unidentified. Obidoxime has demonstrated effectiveness in animals. Thus, as a supplement to treatment with atropine, treatment with obidoxime (250 mg by slow intravenous infusion) should be considered, bearing in mind possible hepatotoxic effects

Diazepam should be administered to control convulsions. It also has value in controlling fear on the part of the patient. An initial dose of 5 mg may be followed by additional doses at 15 minute intervals up to a total of 15 mg.

PHYSICAL COUNTERMEASURES

Protective equipment (self-contained breathing equipment or gas mask, barrier suit) must be used.

The combustion products produced by burning GA are less toxic than the agent. If GA is burning and other considerations permit it, the fire should not be extinguished.

Also refer to 2004 Emergency Response Guidebook (ERG2004) Guide 153.

DECONTAMINATION

Victims

Decontamination of victims is accomplished by removing the victim from the contaminated area, removal of clothing, and removal or neutralization of agent present on the skin. Any visible droplets should be blotted (not wiped) away using an absorbent material (e.g., paper towels, facial tissues, etc.); if available, towelettes moistened with a neutralizing solution should be used. Adsorbant powders may also be used for removal of droplets (in the absence of standard adsorbents, field expedients such as flour may be useful). Adsorbants should be promptly removed. Hair should be thoroughly cleaned using soap and water, with care being taken to prevent wash water from contacting skin.

Property

Surface decontamination may be accomplished using hypochlorite bleach slurries, dilute alkalis, or DS2 decontaminating solution. Note, however, that cyanogen chloride may be generated by the decomposition of GA when bleach-containing decontaminants are used. The preferred decontaminant for tabun for surfaces is a solution of sodium hydroxide 10 wt.% (or greater) in water. Steam and ammonia may be used for the decontamination of confined spaces. Hot, soapy water can also be effective.

GA is of intermediate solubility in water (9.8% at 20°). It hydrolyzes with a half-life of 8.5 hours at pH 7 and 20°, and with a half-life of 7 hours at pH 4-5. Phosphates increase the hydrolysis rate. Note that one of the hydrolysis products is cyanide, and that hydrogen cyanide may be evolved under certain conditions.

COMMON PRECURSORS

• Diethyl N,N-dimethylphosphoramidate
• Dimethylamine
• Dimethylamine hydrochloride
• Phosphorus oxychloride
• Phosphorus pentachloride
• Phosphorus trichloride
• Potassium cyanide
• Sodium cyanide

COMMENTS

Tabun was one of the first nerve agents synthesized. Because it can be synthesized from (relatively) noncorrosive precursors without an an alkylation step, it is perhaps the easiest nerve agent to synthesize in bulk.

Historical Notes

GA was the first organophosphate compound to be identified as a potential chemical agent. It was first synthesized shortly before Christmas, 1936 as a part of research directed at identifying insecticides (specifically, for the control of wooly aphis, a form of aphid) under the direction of Dr. Gerhard Schrader at the Bayer facility at Elberfield.

That Tabun was quite toxic was quickly recognized. In initial experiments, a concentration of 5 ppm killed all the insects in the test chambers. But when, in the course of the tests on insects, Dr. Schrader and a laboratory assistant were exposed to the vapors and strongly affected, it quickly became apparent that the material might have military applications. This was duly reported this to the German government under a law requiring that the government be advised of any discovery with potential military applications. Research was continued, and a "secret" patent (DRP 767511) was issued for the material, now known as Tabun, on 22 July, 1937.

Research was carried out on production methods, and a process which produced Tabun in good yield (approximately 83%) was developed. In 1940, construction began on a plant (the Hochwerk) to manufacture Tabun, now also known by the code name T-83 (the number is said to be a reference to the yield; the material was also designated Trilon 83), at Dyhernfurth (now Bzerg Dolny, Poland). The plant was operated by Anorgana GmbH (a member of the IG-Farben conglomerate) under contract to the German government. After some initial teething problems, production began in 1942, with 675 tons being produced in that year. Production rose to 4,555 tons in 1943, with a high of 7,519 tons in 1944, and in the final months of the war, 120 tons in 1945, for a total of 12,869 tons. This was by far the largest quantity of any of the German nerve agents produced under the Grün 3 (Green 3) program. It was a dangerous process, however, with at least ten workers dying as a result of accidental exposures.

A number of types of munitions were filled with Tabun at the Dyhernfurth facility. Two fill mixtures were used - Tabun-A which consisted of a mixture of 95% GA with 5% chlorobenzene as a stabilizer, and Tabun-B, a mixture of 80% GA with 20% chlorobenzene.

Rumors of the new agents reached the Allies throughout the war, but were largely ignored as propaganda. In 1943, when British Intelligence interviewed a chemist who had worked on the project who provided a description of the agent and its production, the report (filed in July, 1943) was simply ignored.

The Soviets presumably became aware of the nerve agents and their properties when they overran Dyhernfurth. But the first certain knowledge that the Western Allies had of the existence of the nerve agents came when British troops investigated some 105 mm howitzer shells found at a captured ammunition dump in the spring of 1945. The shells had unusual markings - a green ring and the letters GA - and a liquid fill, and were quickly recognized as chemical munitions, but what sort was not immediately understood. The initial report described them as containing:

"...a new type of filling containing 20 per cent chlorobenzene and an arsenic derivative which is under investigation."

Of course, further investigation revealed that the agent was not an arsenic derivative, that it had rather startling toxic properties, and that it was only one of a family of agents.

Tabun was destined to recede from its initial prominence, however. The Western Allies, after investigating the range of German nerve agents, decided that they preferred Sarin (GB) because of its greater lethality, while the Russians, after moving a large part of the Dyhernfurth facility to the Soviet Union and reportedly resuming production, decided to go with both Sarin and Soman (which is even more lethal than Sarin). A large portion of the captured Tabun was disposed of by simply dumping it at sea.

GA has not completely disappeared. The relative simplicity of its manufacture coupled with the wide dissemination of information about its production (frequently in histories) has made it attractive as a "starter" nerve agent for states interested in acquiring a chemical weapons capability.

Thus, when Iraq wanted to quickly produce a nerve agent for use in the war with Iran, they used Tabun, apparently following the German path (a sample obtained from a dud bomb showed a composition comparable for that seen by the Germans when they were starting up). (The Iraqis also compromised to an extent in purification - the agents they used appear to have been only 30-40% pure in some cases). Although eventually the Iraqis too abandoned Tabun in favor of more lethal agents, it was certainly not chance that lead them to start with GA.

It must also be noted that the Iraqi use of Tabun against Iranian Troops near Basra on March 17, 1984 marked a milestone of sorts in the history of chemical warfare: it was the first confirmed use of a nerve agent on a battlefield by one state against another. While it is generally estimated that fewer than 100 casualties resulted from this attack, the use of a nerve agent meant there had been a significant change in the way the use of this most modern form of "frightfulness" was viewed.

Project 112 Testing

Beginning in 1962, a variety of tests of chemical and biological agents were carried out as a result of the Project 112 review of U.S. chemical and biological warfare capabilities. These tests were supervised by the Deseret Test Center, which had been established to conduct them. Some of these tests involved GA. The table below provides a brief synopsis of the tests which are known to have included GA and their objectives.

Selected References and Resources

	Web cbwinfo.com

Return to contents page

Copyright© 1999-2001, 2003, 2005 CBWInfo.com