The Pentagon said on Thursday night that long-term effects from brief exposure to the vapourised sarin nerve gas were unlikely, but the US Veterans' Administration (VA) believes it could be one factor in the mysterious Gulf war illness reported by many US and British veterans.
Few British troops are likely to have been affected by the nerve gas release, although it did pass over British troops, including 32 Field Hospital, in the Wadi al-Batin.
The Pentagon announced the results of a new CIA computer model of the way the sarin nerve gas spread after US troops blew up the Khamisiyah arms depot, 20 miles south-east of Nasiriyah, on the Euphrates, on 10 March 1991. It showed that in the prevailing weather conditions the plume of gas may have drifted nearly 300 miles south and then west before dispersing four days later. This would have taken it over US troops, but not over most of the British forces, who were in central Kuwait.
Immediately after the Gulf war, the US and British authorities denied there had been any release of the Iraqis' huge stocks of chemical weapons, including nerve gas. When the news that US troops had blown up the Khamisiyah dump was first released in June last year, the number of troops exposed was put at a few hundred.
Bernard Rostker, the Pentagon's special assistant for Gulf war illness, said 98,900 people might have been exposed to low level doses of sarin and that the Pentagon had begun notifying them yesterday,
"When rockets were destroyed in the pit area of Khamisiyah on March 10 1991, the nerve agents sarin and cyclosarin may have been released into the air," the letter read.
"If you were with your unit at this time, you may have been in an area where exposure to a very low level of nerve agents was possible".
The Pentagon released maps on the Internet showing the movement of the gas plume. On the first day, it headed due south, on the second south- west and on the third, north-west. On the fourth it contracted to the area around Khamisiyah.
Last year, the Pentagon said about 20,000 US troops had been within 30 miles of the ammunition dump, and might therefore have been exposed. No US troops experienced any noticeable health effects at the time. "Current medical evidence indicates that long-term health problems are not likely from brief low-level exposure to nerve agents", the Pentagon said.
Dr Susan Mather, a VA expert, said: "We know of no risks that this low- level exposure to nerve gas would incur. There was plenty of data on exposure to higher levels of nerve gas - a droplet of which, the size of a pinhead, can kill, but we don't have a lot of knowledge of human beings at that low level."
Many British Gulf veterans now believe the unexplained Gulf war illness, which has affected 1,880 of the 51,000 British troops who were in the Gulf, is caused by the precautions taken against chemical and biological attack, and not by exposure to nerve gas itself. British and US troops took tablets to strengthen their resistance to nerve gas and were inoculated against germ warfare including plague, anthrax and whooping cough.
Organophosphate pesticides, used in vast quantities to counter the flies, have also been blamed. The French, who were not given any of the jabs or tablets, have not suffered from "Gulf war illness". And the nerve gas cloud from Khamisiyah would have passed over French troops.