What do we know?
/ Highly doubtful
/ Low confidence
/ Moderate confidence
/ High confidence
A US intelligence official described assessments regarding the use of chemical weapons as of low or moderate confidence.
When and where could chemical weapons have been used?
Syria's chemical weapons
The White House said for the first time that it has some evidence that Syria has used chemical weapons in its civil war. A look at Syria’s chemical weapons facilities:
Source: Center for Nonproliferation Studies,U.S. Defense Department, GlobalSecurity.com,Journal of American Medical Association, BBC
"Brig. Gen. Itai Brun, chief of research for Israeli military intelligence, told a security conference in Tel Aviv that there was strong evidence that a lethal chemical weapon, likely the nerve gas sarin, had been used in incidents near Damascus and Aleppo on March 19. He said that photographs of victims with foam coming out of their mouths and contracted pupils were signs of sarin use."
"An Israeli intelligence officer who reports to Brun added later that additional satellite images and witness testimony had been used to “conclusively determine” that a nerve agent had been used in the attacks. The officer, who spoke on condition of anonymity because he wasn’t authorized to speak publicly, said that Israel was investigating “nearly half a dozen possible incidents” but that its most conclusive findings were over attacks in the Damascus suburbs of Jobar, Adra and Ataibeh."
How do we know if chemical weapons have been used?
The Organisation for the Prohibition of Chemical Weapons works with the UN to test for the use of chemical weapons under then 1997 Chemical Weapons Convention. While Syria is not a member of the chemical weapons treaty, and not bound to its ban on development of chemical weapons, it is prohibited from using sarin under the 1925 ban on chemical weapons.
According to the U.S. Centers for Disease Control, tests can detect trace amounts of sarin in urine or decreases in plasma or certain enzymes in the blood can indicate its presence. Because these levels vary, repeated blood tests are required to confirm that an individual was exposed to sarin.
Soil samples can be analyzed for phosphoric acid, indicating the possibility that sarin has been present. Because sarin was originally developed as a pesticide, false positives from exposure similar pesticides.
"Obama is dispatching Secretary of State John F. Kerry to Moscow in the next few days to try to persuade the Kremlin to end its support of the Assad regime. ...
"A U.N. investigation of the alleged use of chemical weapons has stalled amid a disagreement with Damascus about access in Syria."
"Some members of Congress and other advocates have urged the administration to begin arming the rebels, to create no-fly zones to protect refugees, or to use military force to destroy or seize Syria's huge stockpile of chemical weapons."
"But White House and senior Pentagon officials fear that U.S. weapons shipments could end up in the hands of Islamic militants, who are playing a growing role in the revolt, or could increase the suffering in Syria without resulting in Assad's ouster."
"Conservative lawmakers and their allies say Obama has raised the bar so high that it is unlikely he will take action. They argue that Iran and North Korea will view his response as a signal that U.S. threats can be ignored."