Monday 19 August 2013

A Chemical Weapon Specialist's Thoughts On The UN Visit To Syria

With the arrival of a UN team in Syria searching for evidence of chemical weapon use in Syria I asked Dan Kaszeta, a chemical weapons specialist, some questions about the investigation.

In general terms, what do you think the UN investigation will involve?

I have no direct experience of UN investigations.  Indeed, this sort of investigative expedition is a rare event with relatively few precedents  What I can do, is speculate as to what I would do  if I were in charge of the investigation.

The UN is scheduled to visit Khan al-Assal, the scene of an alleged chemical weapon attack some months ago, with Russia claiming sarin was the agent used. What is the likelihood of the UN team being able to detect sarin at the scene of the attack?

If sarin had been used at Khan al-Assal, the likelihood of sarin actually being found in some form some 5 months after the alleged event is extremely small.  Sarin evaporates quickly.  It is classified as a non-persistent agent for this reason.  The vapour pressure of sarin is similar to water.  It evaporates at about the same rate as water on a very dry day.   Syria is a warm, dry climate.  Even if Sarin had been used, which, based on various information I have seen is unlikely, it would be long gone.  This is the scientific equivalent of pouring a bottle of vodka in your garden and going back over a month later trying to find the vodka still there.  It isn't a rational expectation and it isn't supported by basic science.

There is also the concept of “scene integrity” to be considered.  The Khan al-Assal site is an alleged crime scene that has been unsecured for five months.  People and objects have come and gone.  There is ample opportunity for things that were at the crime scene to be removed and there is ample opportunity for things that weren't at the crime scene.

There are some relatively rare circumstances wherein a sample of sarin might still be available after this time:

  • An unexploded, sealed munition that did not function as intended. 
  • A shell or rocket fragment collected within a few hours of the incident and sealed in a jar or sealed plastic bag.
  • A shell or rocket fragment containing sarin liquid embedded in some other matter in a way that would prevent evaporation or hydrolysis (reaction with ambient moisture).   
However, given the extreme concerns about the scene integrity, chain of custody, and the time elapsed, the validity of such evidence would be suspect.

There were some reports at the time of a strong smell of chlorine at the scene of the attack, would that be detectable at the scene of the attack?

There are far too many chemical compounds that could potentially cause a “chlorine smell” to make any definitive conclusions.  It should be noted that a chlorine smell is not at all associated with any category of nerve agents.   Also, odours are base on gases, vapours, and aerosols.  There’s no rational expectation that a gas, vapour, or aerosol could be present after the passage of this much time.  In addition, the “scene integrity” concerns above still apply. 

Would it be possible to detect the use of sarin in the blood, hair, urine, or tissue of victims, both the dead and the survivors?

There’s lots of scientific work that has been in this area, as I noted in a previous paper on this subject.  The issue is elapsed time.  There’s little scientific/academic work that addresses the issue of forensic analysis after such a lengthy period of time.  Again, one must view “survivors” and dead bodies as evidence.  Where have they been for this period of time?  There’s no chain of custody or scene integrity. 

Several months after the attack, would victims of the attack still present any symptoms?

It seems highly unlikely.  There is some evidence of miosis (pinpoint pupils) being visible for weeks after exposure, but we are talking about many months in this situation.  

The Russians have claimed a very specific type of rocket was used.  Assuming the remains of the rocket were available to be examined, would the UN team have any chance of being able to confirm it was used to deliver a chemical agent, and would they be able to detect sarin on it?

I think that it is much more likely to be able to evaluate the shape and construction of the rocket to see if it is consistent with a chemical weapon, or if it is more consistent with a conventional explosive rocket. 


More details posts on chemical weapons in Syria can be found here, including more from Dan Kaszeta on sarin.

You can contact the author on Twitter @brown_moses or by email at


  1. After regurlarly reading your blog for some time, I've been getting the impression that the gas attacks most likely haven't been sarin.

    Don't know if you've seen this article, but it airs the theory that Assad might mix nervegas with CS-gas, and that it could be an explanation as to why the gas victims behave in a "non-nervegassed way".

    Any comment on this?

  2. Also worth noting there was a massacre in the town
    Pretty suspicious ...

  3. With this, it is more likely to conclude that no evidence of sarin or any gaseous substance used.

  4. This was very bad what happen in Syria.I think whoever did this disgusting thing ,it must not be happen again and a big step should be rise to stop all this nonsense.
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