The Grand Forks fire on Sept. 15, 1980 received little public attention at the time, in part because the Air Force insisted there was no chance of a thermonuclear accident. What actually happened has been obscured by Air Force secrecy and the reluctance of experts within the nuclear weapons community to speak publicly.
But within that community, Grand Forks is remembered as one of the nation's closest brushes with nuclear catastrophe.
Breathing or ingesting plutonium particles can lead to death, tissue damage or a higher risk of cancer, depending on the amount. And such particles in the soil would remain radioactive for 24,000 years.
"If you breathe (plutonium) in, even the tiniest speck, you get cancer," said Stan Norris, an analyst with the Natural Resources Defense Council.
The near-disaster raises questions about the safety of the nation's aging nuclear arsenal: about 75 percent of the bombs, shells and rockets contain conventional explosives that will go off in a fire.
Experts say a repeat of the Grand Forks incident is highly unlikely because the weapon involved - almost certainly a missile carried inside the plane's bomb bay - has been banned from bombers. But they say the country has stockpiled thousands of bombs whose safety devices are not as up to date as they should be.
A frightening picture of what almost happened in Grand Forks that September evening - when a fire fed by fuel in a B-52's wing tank burned like a blowtorch for nearly three hours - emerged during a closed Appropriations subcommittee on Defense hearing in 1988. An edited transcript was subsequently made available.
Batzel, the witness, was then director of the Lawrence Livermore National Laboratory in Livermore, Calif., one of the nation's three nuclear weapons testing labs. He is one of the world's foremost authorities on such weapons.
Batzel said that if the stiff, 26 m.p.h. wind had blown the fire into the B-52's bomb bay - instead of away from it - it would have detonated conventional explosives in the triggering mechanism of the bombs. Though a thermonuclear blast would not have occurred, the explosion would have blown the plutonium into microscopic bits and thrown it into the atmosphere to drift downwind.
"You are talking about something that in one respect could be probably worse than Chernobyl," Batzel said, referring to the Soviet nuclear reactor accident that spread radiation over a wide area.
"Is that right?" said Sen. J. Bennett Johnston (D., La.).
"Yes, because you have plutonium in the soil and on the soil, which you have to clean up," Batzel said. " . . . I wouldn't want either one."
"That particular fire caused enough heat, then, that it would have caused this?" asked Sen. Dennis DeConcini (D., Ariz.).
"Yes, the aircraft burned for hours," Batzel said.
Batzel said that the "high explosives which are in those particular warheads would have detonated. It would have happened in that environment."
"Do you know that through testing?" DeConcini asked.
"Yes sir," Batzel said.
Now retired, Batzel refused to be interviewed for this article. But Robert Peurifoy, a retired vice president of the Sandia nuclear testings lab in Albuquerque, N.M., confirmed the outline of Batzel's testimony.
"It was one of the more risky incidents we faced," Peurifoy said.
Air Force and Defense Department officials contacted recently downplayed the danger of the Grand Forks fire, saying the Air Force would have taken more drastic measures to fight the fire if the wind had been blowing in a different direction. But they refused to discuss the incident in any detail.
The weapon on the Grand Forks B-52 almost certainly was the SRAM-A short- range missile, Robert B. Barker, a Pentagon nuclear weapons expert, said at a Senate hearing earlier this year. In 1990, Defense Secretary Dick Cheney ordered the missile taken off bombers after the directors of the nation's nuclear weapons labs told Congress that it posed a safety risk.
But the lab directors had been warning the Defense Department about the SRAM-A for more than 15 years before action was taken. They believed that there was a high risk of a nuclear accident if the conventional explosives in the SRAM-A were exposed to a hot enough fire.
"This is apparently what came close to happening in the Grand Forks incident," said Norris of the Natural Resources Defense Council.
Sidney Drell, a Stanford physicist who recently headed a government panel on nuclear weapons safety, said there are several reasons the military has been reluctant to change weapons such as the SRAM-A.
Nuclear warheads have a long shelf life, Drell said, and Pentagon planners do not want to spend defense dollars replacing weapons that are still effective.
Also, the U.S. military takes pride that no life has been lost due to a nuclear weapons accident in the United States.
Still, the Drell panel urged the military to use explosives that do not go off in a fire. It also called for safer detonating mechanisms and "a fire- resistant pit" that protects the explosives. Fewer than 10 percent of the nation's 19,000 nuclear missiles, bombs and shells include such a pit.