DENVER — The U.S. Army plans to begin destroying the nation's largest remaining stockpile of chemical weapons Wednesday.
The first container of mustard agent was moved into an airtight containment building at Pueblo Chemical Depot in southern Colorado, and crews expected to open it and neutralize it later in the day.
"Everybody's really excited, but we're being cautious, making sure all the procedures are followed exactly," said Bruce Huenefeld, manager of the first destruction process to get underway at the depot.
The facility has about 2,600 tons of mustard agent, most of it contained in about 780,000 shells.
Mustard agent can maim or kill by damaging skin, the eyes and airways. It's being destroyed under a 1997 international treaty banning all chemical weapons. It will take four years to destroy the Pueblo stockpile.
Another 523 tons of mustard and deadly nerve agents are stored at Blue Grass Army Depot in Kentucky. Blue Grass isn't expected to start destroying its weapons until 2016 or 2017, finishing in 2023
The destruction process is safe, officials said.
Most of Pueblo's stockpile will be dismantled and neutralized in a highly automated $4.5 billion plant built at the depot.
About 1,400 damaged shells and a dozen metal bottles of mustard agent are considered unsuitable for that plant. They'll be torn open with explosives inside a sealed chamber, and the mustard will be chemically neutralized.
The metal bottles contain mustard that was extracted from the shells for testing.
They'll be the first to be destroyed, followed by the damaged shells, depot spokesman Thomas Schultz said.
The explosion chamber was expected to start operating Wednesday with the destruction of a single steel bottle, officials said, but the automated plant isn't expected to begin work until December or January. Design and construction have taken years, and final testing and training are underway.
Mustard agent is a thick liquid, not a gas as commonly believed. It has no color and almost no odor, but it got its name because impurities made early versions smell like mustard.
The U.S. acquired 30,600 tons of mustard and nerve agents, but it never used them in war. Nearly 90 percent of its original stockpile has already been destroyed.
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