The US is about to begin destroying its largest remaining stockpile of chemical-laden artillery shells, marking a milestone in the global campaign to eradicate a debilitating weapon that still creeps into modern wars.
The Pueblo Chemical Depot in southern Colorado plans to start neutralising 2,600 tons of ageing mustard agent in March as the US moves toward complying with a 1997 treaty banning all chemical weapons.
"The start of Pueblo is an enormous step forward to a world free of chemical weapons," said Paul Walker, who has tracked chemical warfare for more than 20 years, first as a US House of Representatives staffer and currently with Green Cross International, which advocates on issues of security, poverty and the environment.
The work starts less than a year after chlorine gas killed 13 people in Syria in April 2014. International inspectors concluded last month that the gas had been used as a weapon.
Before the chlorine attack, 1,400 people were killed in a 2013 nerve gas attack in Syria, the US said.
Pueblo has about 780,000 shells containing mustard agent, which can maim or kill, blistering skin, scarring eyes and inflaming airways.
Mustard agent is a thick liquid, not a gas as commonly believed. It's colourless and almost odourless but got its name because impurities made early versions smell like mustard.
After nightmarish gas attacks in World War I, a 1925 treaty barred the use of chemical weapons, and the 1997 Chemical Weapons Convention set a 2012 deadline to eradicate them.
Four nations that acknowledged having chemical weapons have missed the deadline: the US, Russia, Libya and Iraq.
The cost of safely destroying the weapons, and concerns about public health and the environment, have slowed the process, experts say. Violence in Iraq also has been an obstacle.
Libya expects to finish in 2016 and Russia in 2020, according to the Organisation for the Prohibition of Chemical Weapons, which oversees the Chemical Weapons Convention. Iraq's completion date is unknown.
The US amassed 30,600 tons of chemical weapons, both mustard agent and deadly nerve agent, much of it during the Cold War. The Army described them as a deterrent, and the US never used them in war.
