A U.S. hydrogen bomb nearly detonated on the nation’s east coast, with a single switch averting a blast which would have been 260 times more powerful than the device that flattened Hiroshima, a newly published book says.

In a recently declassified document, reported in a new book by Eric Schlosser, the superviser of the nuclear weapons safety department at Sandia national laboratories said one simple, vulnerable switch prevented nuclear catastrophe.

The Guardian published the document on Saturday.

Two hydrogen bombs were accidentally dropped over Goldsboro, North Carolina on Jan. 24, 1961 after a B-52 bomber broke up in flight. One of the bombs apparently acted as if it was being armed and fired its parachute opened and trigger mechanisms engaged.

Parker F. Jones at the Sandia National Laboratories analysed the accident in a document headed “How I learned to mistrust the H-Bomb.”

“The MK39 Mod 2 bomb did not possess adequate safety for the airborne-alert role in the B-52,” he wrote. When the B-52 disintegrates in the air it is likely to release the bombs in “a near normal fashion,” he wrote, calling the safety mechanisms to prevent accidental arming “not complex enough.”

The document said the bomb had four safety mechanisms, one of which is not effective in the air. When the aircraft broke up, two others were rendered ineffective. — AP