Fuel-air bomb: how serious a threat?

By David L. Chandler, Globe Staff, 2/06/1991

hen Saddam Hussein renewed his threats last weekend to use "weapons of mass destruction," world attention focused again on Iraq's nuclear, chemical and biological weapons, but not on one other device that some analysts believe Iraq has: fuel-air explosives, often described as the "poor man's nuclear bomb."

Some independent analysts believe that both the US and Iraqi arsenals include versions of the potentially devastating weapons, but say it is not clear whether Iraq or any other nation has succeeded in perfecting them. If not, the bombs may be less powerful in reality than they are in theory. Theory holds that they could pack the explosive punch of a small "tactical" nuclear warhead. The bombs work by spraying a fine mist of highly explosive fuel, such as methane, through a large volume of air -- a sphere up to 150 feet in diameter -- and then igniting the fuel-air mixture with a spark or small explosion. By using oxygen from the surrounding air for combustion rather than carrying it in the explosive material itself, the bombs can produce more bang for the weight. Forty percent of the weight of a conventional explosive consists of oxygen chemically locked up in the compound, according to Jane's Air-Launched Weapons.

Some press and television reports have suggested that fuel-air bombs may have been dropped over Iraq by allied forces last weekend, but a Pentagon spokeswoman said yesterday that she could not confirm the use of such weapons, or even that the United States has them.

Henry Dodds, editor of the British monthly Jane's Intelligence Review, said in an interview that Iraq is known to have been working on fuel-air bombs. "We know they did some explosive tests a few years ago," he said, "just at the end of the Iran-Iraq war."

There were reports in the British press last year that Iraq had been negotiating to buy fuel-air bombs from a Chilean arms company. If Iraq has acquired the devices, Dodds said, it could add an important weapon to its arsenal. "As a battlefield weapon, it's really quite good," he said. "effective, that is. Of course it's not good."

An effective half-ton fuel-air bomb, Dodds said, would be "equivalent to a low-yield battlefield nuclear weapon of about 10 tons explosive yield."

Theoretical calculations indicate that the explosion would produce a shock wave with an overpressure -- a measure of the strength a blast -- of 4 pounds per square inch at a distance of 360 feet -- at least five times greater than the shock wave from an equal weight of conventional explosives. Dodds said an overpressure of just 2 pounds per square inch "is lethal to infantry in the open."

Such explosions are also "very effective against buildings and aircraft," he said. The aerosol mist of fuel can penetrate buildings, bunkers and vehicles, causing them to explode from the inside when the vapor is ignited.

But the theoretical power of fuel-air explosives has never been openly demonstrated in a real weapon, said Duncan Lenox, a former Royal Air Force engineer who is now editor of the annual reference book Jane's Strategic Weapons.

"The difficulty," Lenox said, "is to spread the aerosol evenly over such a wide area and ignite it at precisely the right time. There is no evidence that anybody has mastered it."

The basic concept is not new. Early versions of fuel-air explosives were used by US forces in the late years of the Vietnam war, primarily to clear patches of jungle as helicopter landing pads. But, Lenox said, the early bombs fell far short of the explosive power predicted by theory, and tended to burn rather than explode.

"A lot of people claim to have developed fuel-air weapons," Lenox said, "but there's no evidence that they're beyond the crude weapons used in Vietnam."

John Pike, an aerospace analyst with the Federation of American Scientists in Washington, said the explosive is "really good for giving a wide area a good solid thump," making fuel-air bombs potentially useful for clearing an area of land mines, for example. But he said they are unlikely to have significant or widespread applications in the gulf war.

Pike said he believes the United States scrapped its fuel-air explosive program about five years ago and said he would be surprised if there are still such weapons in the US arsenal.

The Soviets have claimed to have developed such bombs as well, Lenox said but, once again, "it's not proven."

There have been published reports that the Iraqis used fuel-air weapons against Iranian oil platforms during the Iran-Iraq war, and one study from the US War College suggested that what appeared to be chemical attacks during the war may actually have been the use of fuel-air explosives, which can cause similar skin burns.

Lenox, however, said he doubts that the Iraqis have effective versions of the weapons. Given Iraq's defiant declarations of readiness to use chemical, biological and nuclear weapons, he said, if Iraq had effective fuel-air weapons "they would have announced it."