It was meant to be a routine maintenance procedure. On September 18, 1980, two airmen entered Launch Complex 374-7, an underground silo outside Damascus, Arkansas, to service a Titan II intercontinental ballistic missile (ICBM). About 6.30pm one of the men dropped a wrench socket. It fell into the silo, bounced off the ICBM and holed a fuel tank.
The dropped socket triggered a series of events that almost levelled Arkansas. Oxidiser sprayed out.
Mixed with rocket fuel it would explode, a terrifying prospect as the ICBM was armed with a nine-megaton thermonuclear warhead, three times as destructive as all the bombs used in World War II, including both atomic bombs dropped on Japan.
By 9pm Complex 374-7 had been evacuated as police cleared nearby communities. At 3am the missile exploded, blasting the silo's 670-tonne door into the sky. It fell 180m away. The warhead was found near the site's entry gate. Its safety devices had worked. One airman was killed and 21 people injured.
It was a very near-run thing.
This incident, which resulted in an estimated US$245 million ($295.5 million) clean-up bill, with the site entombed, is one of many close calls involving United States nuclear weapons. In January 1978 an oxidiser leak at Complex 374-7 released a toxic plume, necessitating a civilian evacuation. No one died.
The 1980 episode is recounted by Eric Schlosser in Command and Control: Nuclear Weapons, the Damascus Accident, and the Illusion of Safety, a new book that investigates a decades-long secret history of terrifying US nuclear weapons near-catastrophes.
According to the Pentagon there have been 32 serious mishaps. But Schlosser says many hair-raising accidents were suppressed and cites at least 700 "significant" episodes, involving 1250 nuclear weapons, between 1950 and 1968.
In one 1961 accident a B-52 Stratofortress broke up in mid-flight and jettisoned two 24-megaton atomic bombs over North Carolina. One bomb hit the ground at 1100km/h and disintegrated without exploding.
The second drifted down by parachute, its arming systems activated. Millions of lives were spared when an arm/safety switch stayed on safety.
The US journalist, who wants nukes abolished and is best known for Fast Food Nation, reminds us that while the Cold War balance of terror (which assumed tens of millions would die in a MAD, or Mutually Assured Destruction scenario echoed by the 1964 film Dr Strangelove or: How I Learned to Stop Worrying and Love the Bomb) between the US and the Soviet Union has ended, the risk of a nuclear weapons accident has not.
"If we don't greatly reduce the number of nuclear weapons in the world, or completely eliminate them, a major city is going to be destroyed by a nuclear weapon," Schlosser told American news magazine Mother Jones. "It's remarkable - it's incredible! - that a major city hasn't been destroyed since Nagasaki."
As memories of the Hiroshima and Nagasaki bombs and the MAD era recede he hopes his book will restart a debate about nuclear weapons.
Nuclear weapons can be safe 99.9 per cent of the time, but 0.1 per cent error spells nuclear holocaust. Even when nukes work things do not always go as designed: just 1.38 per cent of the nuclear core in the atomic device detonated above Hiroshima in 1945, killing 80,000 people, exploded.
"We escaped the Cold War without a nuclear holocaust by some combination of skill, luck and divine intervention, and I suspect the latter in greatest proportion," an Air Force general told Schlosser.
And while ageing equipment and facilities heighten risks, simple mistakes - dropping a socket, entering the wrong computer code, mistaking moonrise for enemy missiles - have courted nuclear disaster.
In 2007 six nuclear warheads were mistakenly loaded on to a B-52 bomber in Wyoming and flown 2400km across the US. In 2010 a unit responsible for one of the largest nuclear weapons storage dumps at Kirtland Air Force Base was stood down for safety failures. And in August a missile unit at Malmstrom Air Force Base flunked a "surety" check that prevents an ICBM being accidentally armed or launched.
A 2010 Defence Department study found "safety, security and environmental issues" at ageing facilities "a significant challenge". At the same time the US admits nuclear weapons are "poorly suited to address the challenges posed by suicidal terrorists and unfriendly regimes seeking nuclear weapons" and said its arsenal could be reduced to between 1000 and 1100 warheads without jeopardising security. The New Strategic Arms Reduction Treaty (New START), which began in 2011, limits Russia and the US to 1550 long-range nuclear weapons each by 2018.
"That's actually a misnomer," explains Lisbeth Gronlund, co-director of the global security programme for the Union of Concerned Scientists. "It's an underestimate of how many bombs they'll be allowed to have."
New START places no limit on the actual number of warheads, such as non-deployed and tactical weapons. So how many nuclear weapons do we have to worry about? According to Hans Kristensen and Robert Norris, at the Bulletin of the Atomic Scientists (BAS), 10,000 weapons, overwhelmingly possessed by the US and Russia, exist. "Several thousand" more retired nukes await dismantlement in both nations.
"Both US and Russian land-based missiles are on high alert," says Gronlund. "This isn't addressed by New START. If something goes wrong hundreds can be fired. The consequences are enormous." The BAS's Doomsday Clock, now at 11:55 p.m. (midnight is doomsday), might rewind and make us all safer if missiles and warheads were kept separate and US missiles withdrawn from Europe, as Gronlund advises.
Meanwhile, the Pentagon wants to upgrade its arsenal, refurbishing existing weapons rather than building new warheads. Crucially, this does not involve tests, banned since 1992 - among the surreal legacies at the Nevada Test Site is a cancelled subterranean test; a deep shaft with cables radiating to computer-laden trailers like spokes on a wagon wheel.
The overhaul would mean funding nuclear laboratories, building a new uranium processing plant, and replacing ageing delivery systems with a new "triad" of aircraft - the B-52 dates from the 1950s - submarines and missiles over coming decades.
The existing triad costs US$55 billion a year to maintain or US$600 billion over the next decade. The Arms Control Association says 12 new submarines will cost about US$350 billion, heavy bombers at least US$68 billion and missiles billions more.
Is there any rationale for retaining nuclear weapons when their use might invite mutual annihilation? The dilemma remains unanswered. Meanwhile, nuclear disaster may be just a mishap away.