The U.S. Army has begun the process of destroying the nation 's last supplies of chemical weapons which are contained in almost 800,000 artillery shells . The terrifying arsenal is contained at the Pueblo Chemical Depot in southern Colorado . The first batch of the mustard agent was destroyed after scientists used explosives to open up a sealed container and flooded it with a second chemical to neutralise the liquid . Scroll down for video . Technicians will take four years to eliminate almost 800,000 artillery shells containing mustard agent . The chemical agent , commonly known as mustard gas , is actually a liquid which smells like the condiment . It is estimated that there are 2,600 tonnes of the chemical agent contained within 780,000 shells at the facility . Bruce Huenefeld , who is managing the destruction process said : 'Everybody 's really excited , but we 're being cautious , making sure all the procedures are followed exactly . ' 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 is n'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 neutralised in a highly automated $ 4.5 billion plant built at the depot . The Pueblo Chemical Depot in southern Colorado has a method of destroying damaged chemical shells . The United States said it never used mustard agent in any conflict and agreed to destroy their stockpile . About 1,400 damaged shells and a dozen metal bottles of mustard agent are considered unsuitable for that plant . They 'll be opened with explosives and neutralised in the sealed chamber , which sits inside an airtight structure near the larger automated plant . The metal bottles contain mustard that was extracted from the shells for testing . A single bottle was the first container to be opened and neutralised Wednesday . Crews were waiting for the neutralisation to finish before draining the chamber , rinsing it and then removing the remains of the bottle . Once all the bottles are destroyed , crews will start work on the damaged shells , depot spokesman Thomas Schultz said . The automated plant is n'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 per cent of its original stockpile has already been destroyed , mostly by incineration . The depots in Colorado and Kentucky are using chemical neutralisation because residents and officials expressed concerns about the vapor from incineration .
The United States agreed to destroy its mustard chemical agent in 1997 . The chemical agent is commonly called mustard gas despite being a liquid . Almost 800,000 artillery shells are being destroyed over the next four years . The United States stockpiled Another 523 tons of the liquid .