The military and diplomatic hurdles to corralling Syria's chemical weapons are difficult enough, but suppose it's done: Then what happens to that deadly stockpile?
You can't just burn it. You can't bury it. And you sure can't shoot a missile at it. All those methods run the risk of spreading lethal agents, causing mass deaths and worsening an international crisis.
Based on past history, it could take billions of dollars and at least a decade to destroy Syria's estimated 1,000 tons of chemical weapons — a task complicated by the fact that removing those weapons from the mix would not end the country's civil war.
So how does the process of destroying chemical weapons work?
Assuming Syria follows through on its promise and joins the international ban on chemical weapons, the process is actually up to ... Syria. The Assad government would have to detail its stockpile for the first time, and lay out a plan for eliminating the weapons and the production facilities. The OPCW would have to give its approval, and inspectors would monitor the process from start to finish.
The procedure typically involves draining the chemical agents (for example, blister agents like mustard gas, or nerve agents like sarin, tabun or VX) from their munitions, and then incinerating them. Under the terms of the chemical weapons ban, which went into force in 1997, the United States already has destroyed 90 percent of its own 31,500-ton chemical weapons stockpile through incineration.
The incineration process doesn't mean you just put VX in a barrel and set it on fire: There's a complicated procedure to extract the agents, subject them to high heat and dispose of the combustion products safely. Even the smoke that goes up the smokestack should be filtered. Greg Mahall, a spokesman for the U.S. Army Chemical Materials Activity, told NBC News that the disposal facilities have "various circles of safety" that require some workers to wear protective moonsuits.
"Once the weapons got into a certain area of the plant, they were never touched by human hands," he said. "It was all robotics."
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The United States started getting rid of its obsolete chemical weapons even before the international ban took effect. Since the late 1980s, the disposal process has cost the Pentagon more than $35 billion, and it's not over yet.
What complications can come up?
The chemical weapons ban applies to 189 nations — but 16 years after it took effect, about 30 percent of the weapons that have been declared still haven't been destroyed. Both the United States and Russia missed last year's deadline for finishing the job.
Mahall said the Pentagon's process has run into snags because some of the older weapons had degraded over time and posed extra safety problems. For example, some of the munitions "popped like a Champagne cork," unexpectedly spraying out mustard gas.
"Safety ran this program, so anytime we had an issue, we stopped," he said.
There are added complications for countries like Syria, having to do with cost and lack of expertise. Syrian leader Bashar Assad will probably want his Russian allies to lend a hand, but that's likely to be met with a wary response from the United States and its allies. It could take years to work out the diplomatic tangles and set up the infrastructure for disposal, Patel said.
The biggest complication has to do with the fact that Syria is still in the midst of a civil war. No one can be certain who will be in charge next year, let alone in 10 years. Libya shows what could go wrong: Moammar Gadhafi promised in 2003 that he'd get rid of his country's chemical weapons — but in 2011, inspectors had to suspend their work due to Libya's civil war.
Can't they just move the weapons?
Patel's first impulse was to rule out trying to move the deadly chemicals to another country. "It's incredibly dangerous," she said. But then she weighed the risk of transporting the weapons against the risk of keeping them in the midst of a shooting war.
She then threw in another factor that might tip the balance in favor of moving the stockpile out of Syria, at least in the minds of U.S. policy planners: "The conventional weapons would be denied not only to the Assad regime, but also to any regime that might come after," she said.
How would we know if Syria was cheating?
That's a problem. "Any program to destroy chemical weapons depends on the accuracy of the initial information," Patel said. And governments have been known to lie about that in the past. In late 2011, the interim Libyan government that took over after Gadhafi's ouster reported finding a previously undeclared cache of chemical weapons.
If there's any suspicion that the Syrians are holding back, the OPCW could conduct challenge inspections to root out suspected sites. But the inspectors won't shoot their way in. "At the end of the day, the country you're inspecting has to agree," Patel said.
Even if Syria promises to get rid of its chemical weapons, the United States and other countries might have to continue holding out the threat of military force for years to come — to ensure that Assad or his successors keep those promises.