A UN investigator collecting samples last week at the site where rockets fell in Damascus’s eastern Ghouta suburb (Image: Ammar al-Arbini/AFP/Getty Images)

John Kerry claimed this week that the US now has evidence that sarin was used to kill more than 1400 civilians in the 21 August attack in Syria.

If that is the case, then while any US strikes on Syria may focus on military bases, they might also seek to put chemical stockpiles out of action using “agent defeat” weapons. Since 1998, the Pentagon’s Defense Threat Reduction Agency (DTRA) has been developing weapons to attack chemical agents without spreading them. But any attempt to do this would be risky.

The CBU-107 Passive Attack Weapon (PAW) punctures chemical storage vessels without explosives. Delivered at high speed, the 450-kilogram bomb splits mid-air and rains down more than 3700 steel and tungsten rods over an area 60 metres across.


Sarin, like most chemical weapons, is heavier than air, does not travel far at ground level and is degraded by the action of sunlight and oxygen. But PAW would only be suitable where stockpiles are well away from civilian areas and when there is little wind.

Suspected sites of chemical weapons production

Burn it up

The BLU-119/B CrashPAD destroys chemical agents more rapidly. This 900-kilogram bomb contains a small explosive charge to rupture storage vessels with blast or shrapnel, and 300 kilograms of white phosphorus, which burns at up to about 2700 °C.

Sarin is combustible and the high temperatures would quickly break it down. However, any intact chemical agent could be carried high into the air on the thermal updraught and could travel for long distances.

These are the only agent defeat weapons officially in the arsenal. However, the DTRA has sponsored research on a range of other options that may already be available.

These include foaming thermite, incendiaries, high-energy explosives and high-temperature mixtures similar to rocket fuel. One such DTRA option, a warhead casing made of explosive reactive material, was evaluated for use in a cruise missile in 2012.

Drone eyes

Any agent defeat strike would involve planning with the US Air Force’s simulation tool, called Serpent. This combines models of blast effects, atmospheric dispersion and the rate of neutralisation of chemical agents to predict the pattern of “collateral hazards” from striking a chemical target with a range of weapons. However, the model needs details of the target, which may be lacking.

The DTRA also aims to assess the effects of a strike as soon as it happens, using a miniature drone released from the tail section of a bomb seconds before impact. This could provide immediate warning if a plume of toxic smoke is released.

However, even with advanced weapons and planning tools, the scale of the task might make it impossible.

“The total tonnage estimates varied from 10,000 down to hundreds of tons and their distribution into dozens of locations, making the whole idea questionable,” says James Ketchum, who directed human research at the US Army’s Edgewood Arsenal in the 1960s. “It could not be comprehensive and explosions could release intact lethal gas with fatal results, even if done with sufficient heat.”

Biophysicist Brian Hanley notes that the components for sarin may be stored separately, because it is usually only mixed shortly before being used (or in some weapons, only when fired) – but bombing storage sites could still cause mixing to occur. “I think that the far better choice if the intent is to destroy sarin munitions, is to go in on the ground, capture, remove and then disassemble and drain them safely,” he says.