Hay’s evidence was passed for analysis to Porton Down, Britain’s chemical warfare laboratory in Wiltshire. There, a scientist noticed a flake of paint on the metal shard. It was found that the material behind it tested positive for sarin.
The OPCW has portable equipment for running tests in the field, but Sellstrom’s team will collect samples and send them to laboratories that make up the OPCW’s global network. One is Porton Down. Other labs are in China, Russia, Japan and the US. Samples sent for analysis are worthless if there is any possibility of their having been tampered with, so they are all closely guarded.
In April, the White House said the “chain of custody” of samples that the US had tested was unclear, a problem that lay behind its statement in which said it believed with “varying levels of confidence” that Syria had used the weapons.
Inspectors are unlikely to find sarin in the soil long after an attack, but traces of its breakdown products might show up. Sarin first breaks down into a chemical called isopropyl methylphosphonic acid (IMPA), generally regarded as proof positive.
“There is no other nerve agent containing the structural features of IMPA that is known to be mass-produced, weaponized or fielded,” one serving chemical weapons inspector said.
The inspectors will also test medical sample for traces of IMPA.
“My sense is that it’s probably worth [the UN] going in. They’d be the only party who really have an interest in the truth,” Duelfer said. “If they do this, it’s a deterrent, and that is a supporting element of trying to keep chemical weapons under control, because of the threat that it could get into the wrong hands.”