A fire in a Wyoming missile silo last spring exposed more problems in the oversight of the nation's nuclear intercontinental ballistic missile arsenal, but posed no threat of nuclear detonation or radiation release, Air Force Space Command said Thursday.
The command, headquartered at Peterson Air Force Base, released an accident investigation report Thursday on the silo, which caused more than $1 million in damage.
It had made no previous announcement of the incident.
The Air Force has been under fire for months for failure to properly safeguard nuclear weapons in other incidents that led to the firing of the service's top civilian and military leaders and discipline for 17 officers linked to nuclear problems.
The fire was May 23 at a silo 42 miles east of Cheyenne, Wyo,, where the Minuteman III missile is stored, ready for firing in an unmanned, underground launch facility. The command said it waited for the investigation to be completed before releasing a report.
An Air Force Space Command spokeswoman said the fire, caused by a faulty battery charger in a storage room, extinguished itself from a lack of fuel and was discovered later by repair crews looking for wiring problems on the cables connected to the missile.
"This was no danger to the public and no danger of release or launch," said the spokeswoman, Maj. Laurie Arellano.
Problems revealed by the investigation include unclear instructions on the installation of parts for the battery charger, quality assurance issues and the use of duct tape on cables, the command said.
The Minuteman III carries a city-leveling warhead that contains plutonium, beryllium and uranium. The warhead has an estimated maximum explosive yield of 330 kilotons, the equivalent of more than 30 of the bombs dropped on Hiroshima in 1945, experts said.
The nation's missiles have been kept ready for launch within minutes of a presidential order since the 1960s.
Experts said the risk of the fire causing a nuclear catastrophe was miniscule, but still possible.
The Minuteman III is powered by a volatile solid rocket booster that if ignited in a sealed silo would destroy the weapon and possibly damage the nuclear warhead. Safety features on the warhead would prevent fission and a nuclear detonation, but damage to the device would result in a release of radioactive material, experts said.
The blaze was not discovered immediately because launch crews monitor the silos remotely from control facilities miles from the missiles. The crews did get warning alarms for an electrical problem and excessive heat.
Space Command said the fire never reached the missile launch tube and was limited to the equipment room, meaning the booster and warhead were never in jeopardy.
The missile remained on "alert status," ready for launch, until stand down for fire-related repairs, the command said.
John Pike, a nuclear expert with the think tank GlobalSecurity.org, said the report, which revealed that duct tape was being used in the silo, is cause for serious concern.
"The notion that you're patching up your H-bombs with duct tape is not encouraging," Pike said. "You also have to wonder if you have this sloppy activity that is revealed by a fire happened, how much other sloppy activity has not been detected."
Pike said if the fire had escaped the equipment room and ignited the missile, radiation could have contaminated the silo and surrounding area.
"You could have a pretty good cleanup job," Pike said.
Missile silos are designed to protect the weapon from fire, said Chuck Penson, historian with the Arizona-based Titan Missile Museum outside Tucson.
"They go through all sorts of disaster scenarios when they are building those things," Penson said.
Fire in a Titan missile silo caused one of the nation's most serious nuclear mishaps outside Little Rock, Ark., in 1980. Flames ignited the Titan's liquid-fueled booster and blew the silo's 750-ton blast door a quarter mile away. Parts of the missile, including its warhead, were sent flying in the blast, that injured 20 and killed one man.
The missile's warhead was recovered, and the Air Force said no radiation was released.
The Air Force announced last week that its moving control over nuclear weapons under a single command reminiscent of the Cold War-era Strategic Air Command in a bid to fix oversight problems.
This year, the Air Force found a B-52 bomber crew unknowingly carried nuclear weapons on a cross-country flight. Another investigation found that nuclear missile fuses had been mistakenly sent to Taiwan from an Air Force parts depot.
In response to those problems, Space Command examined its nuclear programs and started reviews including no-notice inspections of missile sites.
The command said the fire led commanders to examine instruction manuals, inspect battery chargers at missile sites and order the removal of flammable materials, including duct tape, from silos.
Critics say the fire indicates continuing woes in the Air Force's nuclear deterrent.
"I think what it suggests is there is a laxness about nuclear weapons that's creeping into our military," said Kennette Benedict, publisher of the Bulletin of the Atomic Scientist, an organization best known for its Doomsday Clock, representing the threat of nuclear Armageddon. "If we're keeping the missiles on such a high-launch readiness we need to ensure we're keeping them secure and safe."
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