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As we just heard, President Obama mentioned evidence that chemical weapons had been used in Syria, but he said intelligence agencies are still seeking proof to back that up. In the meantime, a physicians' organization is trying to help medical workers in Syria to recognize the signs of a chemical attack.
As NPR's Christopher Joyce reports, their effort is meant to save lives, but it could also generate evidence that governments are looking for.
CHRISTOPHER JOYCE, BYLINE: Proving that someone has violated the international taboo on chemical weapons can be very hard. Today, President Obama said, yes, there's evidence that someone used them in Syria's civil war, however...
PRESIDENT BARACK OBAMA: We don't know how they were used, when they were used, who used them. We don't have a chain of custody that establishes what exactly happened.
JOYCE: If they have been used, Syrians are at risk. That's why Physicians for Human Rights is setting up a network to get fact sheets about chemical weapons into the hands of Syrian physicians. This group has a long record of working with medical professionals in trouble spots to protect civilians and reveal war crimes.
The fact sheets list the symptoms of exposure to nerve gases, like sarin and VX or to mustard gas. They explain how to treat people and how doctors can avoid being contaminated themselves. Susannah Sirkin runs the group's international operations. She says, getting this information to Syrians is also important to rule out false alarms.
SUSANNAH SIRKIN: There are times when symptoms may look to doctors as if they were caused by chemical warfare agents. They might mistake other kinds of injuries and harms in a hot conflict with chemical warfare agents.
JOYCE: False alarms could cause panic or, as happened in Iraq, lead the U.S. military to take military action based on inaccurate claims about weapons of mass destruction. The fact sheets also explain how to take samples of blood, urine and hair from patients and preserve them as evidence.
SIRKIN: Obviously, if these weapons are being used, have been used or might be used soon, it's in everyone's interest that this be known and that they be identified.
JOYCE: That sample analysis would likely be done outside Syria. Alastair Hay is a toxicologist at the University of Leeds who's advised the British government on chemical weapons. He's also working with Physicians for Human Rights. Hay says the nerve agents leave a trail in the body. They attack a crucial enzyme that normally works like an on-off switch between nerves and muscles. A nerve gas eliminates the off signal.
ALASTAIR HAY: Basically it's on, on, on, on, on all the time, so you then get a whole range of effects. It's absolutely dreadful.
JOYCE: Terrible headaches, sweating, seizures, respiratory failure leading to death. But other ailments produce similar symptoms, pesticide exposure, for example. Hay says the gold standard of proof means tracking down the nerve agent itself in tissue samples.
HAY: The chemical nerve agent will be attached to the enzyme. It physically inactivates the enzyme and remains attached to it.
JOYCE: Physical samples of nerve agent in soil are harder to get because nerve gas evaporates quickly. But Hay and Physicians for Human Rights succeeded in doing that in 1992. They brought back soil and a contaminated piece of a bomb from northern Iraq, confirming that Saddam Hussein's forces gassed Kurdish civilians there.
Hay notes, however, that getting samples is just the start. To make a legal case, whether it's against the Syrian government or opposition groups, you need an ironclad chain of custody.
HAY: You need to be able to have somebody swear, if you like, that the material was in their custody at all times, whoever it is with before it gets to a laboratory.
JOYCE: For the moment, Physicians for Human Rights is focusing on educating Syrians about the health risks. The fact sheets are being circulated to people traveling in and out of Syria and are available on the group's website.
Christopher Joyce, NPR News.