Frigid Fail-Safe

For all its growing missile prowess, the U.S. still keeps squadrons of nuclear-armed B-52s constantly patrolling the skies within reach of Communist borders, both to respond to any nuclear attack and to act as a deterrent to one. In the course of their duties, on land and in the air, the B-52s have had twelve announced nuclear-weapons "mishaps," the most famous being the collision of a B-52 and a refueling tanker over Palomares, Spain, in 1966.

Last week No. 13 occurred. One of the huge eight-engine bombers, patrolling the Arctic stratosphere on an air-alert mission, caught fire and headed for the U.S. Air Force Base at Thule, Greenland, to attempt an emergency landing. As smoke filled the cabin, the seven crewmen parachuted; all survived except the copilot, whose chute failed to open. Just 7 1/2-miles short of Thule, the B-52 crashed on the rough ice pack of North Star Bay and exploded.

Recurring Question. The accident was greeted with the usual outcry that seems to surround publicity about things nuclear. In Denmark, which has an agreement with the U.S. that nuclear-armed bombers will not use Greenland bases, students marched in the streets. The Russians predictably charged that the U.S. was endangering the whole world, and peace groups picketed and protested angrily. But the ordinary newspaper reader was troubled by a nagging question that recurs with every accident: Could the crash of a nucleararmed plane set off a hydrogen explosion? The answer is no.

An interlocking labyrinth of safety Jocks, switches and devices has prevented any of the 13 "mishaps" from producing a full-scale "yield" detonation. Always unarmed except on presidential order, H-bombs are designed with a system of safeguards so painstakingly complex that the chances of an accidental nuclear blast are infinitesimal. For all the science-fiction myths and nuclear-horror stories, a hydrogen weapon is extremely and deliberately difficult to detonate--even for a skilled B-52 crew.

The reason is that the maze of safety checks is built around the necessity for a perfectly timed implosion, or spontaneous inward burst, of the miniature atomic bomb that every H-bomb contains. This proper A-bomb implosion, which produces enough neutrons to generate a thermonuclear explosion, occurs only when the hydrogen bomb's outer segments of TNT are triggered simultaneously. If they are off by as much as a split second, the H-bomb aborts, with little or no nuclear action or dangerous radioactivity.

Precise Pattern. To arm a hydrogen weapon for firing, which means creating an electrical ignition of all of the bomb's TNT segments at the same instant, B-52 airmen must perform a ritualistic procedure requiring at least 20 minutes of thoughtful work. Unlocking arming mechanisms from a little black box, two or more crewmen operate an intricate combination of manual and electronic seals, switches and interlocks --some dual and others independent--in a pattern so precise that any misstep means starting anew on the entire arming sequence. Only on its successful completion does the bombardier's gloved hand reach for the fateful switch.

Thus far, the H-bomb's fail-safe systems have not been foiled even by shattering falls from high altitudes, as happened at Palomares. In that accident, two hydrogen bombs split open on impact and spilled plutonium, dusting nearby farms, which had to be tediously decontaminated. The same kind of low-level alpha radiation, officially described as "negligible," was discovered on the icebound bay off northwestern Greenland last week. The U.S. airmen who detected the radioactivity reached the blackened, 500-yd.-long crash site on Eskimo dog sleds, the only means available in the swirling snow and 50-m.p.h. winds of the dark Arctic winter.

Burial Problems. In 25DEG-below temperatures, a 75-man team of Air Force and civilian experts sent in under Major General Richard O. Hunziker, SAC deputy chief of staff for materiel, moved ahead with search-and-recovery operations. They soon found assorted bomb fragments and debris, including four parachutes that had been stored in the weapons' tail assemblies, strong indications that all four H-bombs were smashed to bits in the skidding crash and explosion. But some of the nuclear machinery may have melted into the 8-ft.-thick ice or sunk below into 800 ft. of water, which will pose problems in the expected later effort to collect as much wreckage as possible for burial. Unless the small amount of radiation is ruled harmless, the recovery team may face the long task of breaking up and disposing of hundreds of square yards of contaminated ice.

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