the home of online investigations

You can support the work of Bellingcat by donating through the following link:

Khan Sheikhoun, and the Persistence of Conspiracy Theories and Sarin

August 3, 2017

By Eliot Higgins

Translations: Русский

Much like the August 21, 2013 Sarin attacks in Damascus, the April 4, 2017 Khan Sheikhoun Sarin attack has given birth to a range of theories about what did or did not happen. Despite theories presented by various parties that the attack did not involve a Sarin/Sarin-like substance or that the attack was faked, even Russian and Syria has agreed with the finding in the July 4th OPCW-FFM report on Khan Sheikhoun, as per the statement of Edmond Mulet of the OPCW-UN Joint Investigative Mechanism (JIM) on July 6, 2017:

“Yesterday, in the Hague, there was a meeting of the executive council of the OPCW and all member states – all member states – recognised and accepted that Sarin, or Sarin-like, was used in Khan Sheikhoun, was present in Khan Sheikhoun, was dispersed in Khan Sheikhoun. So that is a fact. Everybody, including the Russian Federation, including the Syrian government, have accepted that fact. “

Despite this, there are still some who cling to the idea that the videos and photographs taken at the scene of the attack, in particular those showing rescue works treating victims and filmed at what is reportedly the impact site, were somehow faked. There are two ideas seized upon to “prove” that the attack was faked: that rescue workers showed no signs of Sarin exposure despite their proximity to victims, and that the presence of individuals close to the impact site that show no signs of Sarin exposure. A popular example of this is shown below:

The key issue at hand is the persistence (or persistency, as many technical documents refer to) of Sarin in the environment. In regards to chemical weapons, persistency has been defined in a number of ways, but broadly speaking it is how long a chemical agent is present in an environment before it disperses or breaks down. Chemical agents are often put into two categories, persistent and non-persistent, although the OPCW uses a scale of low to very high, with Sarin rated as low. Other chemical agents used as chemical weapons in the conflict, according to the OPCW, include sulfur mustard, with a very high rating for persistency, and chlorine, rated low for persistency.

But, in the context of Khan Sheikhoun, what does low or non-persistency actually mean? A number of studies have been done on the persistency of Sarin. The 2013 Norwegian Defence Research Establishment (FFI) report “Chemical warfare agents and their interactions with solid surfaces” defines chemical warfare agents as “considered persistent if it remains able to cause casualties for more than 24 hr to several days after it was released, whereas a non-persistent one dissipates or loses ability to cause casualties after 10 to 15 minutes,” and uses the following chart to demonstrate the persistency of various chemical warfare agents:

The temperature range that Khan Sheikhoun experiences around the time of year the Sarin attack took place would be around 7°-23° Celsius, depending on the time of day, according to historic weather simulations.

Another publications containing data on the persistence of Sarin is the “Summary Report on a Database for Predicting Consequences of Chemical Disposal Operations,” published by the Edgewood Arsenal in 1973. This report defines persistency as “the volatilization time for 99% of that part of the agent that evaporated off, and was recovered from, the vapor state.”

Based on the reports definition of persistency, it states the “times for 99% removal of GB (Sarin) ranged from 2.5 to 24 hours”, depending on the type of soil and temperature. In the case of Khan Sheikhoun the impact site (shown below) was the middle of a road, and while road surface were not tested in the above study, it would be reasonable to assume it would be closer to coarser soils in terms of volatilisation:

It is also worth noting that samples from multiple sources taken from the crater were tested by the OPCW, and Sarin was identified in those samples. This includes samples taken by an unnamed individual on behalf of the Syrian government, from the crater were also tested by both the OPCW and the Syrian government agency, the Syrian Scientific Studies and Research Center (SSRC), as shown in the below table:

In the case of Khan Sheikhoun, the lethality of Sarin around the impact site would have reduced rapidly after the initial impact, and being present at the site would not have been the instant death sentence that some people would have you believe. Those videos and photographs cited as proof of fakery and conspiracy, showing people close to the impact crater, were posted several hours, if not days, after the attack. The video showing the collection of evidence from the attack site that is has been frequently used to push theories of fakery was in fact uploaded over 48 hours after the attack, with no indication it was filmed close to the time of impact:

For those who still doubt the short/non-persistency of Sarin, there are earlier examples of Sarin attacks where unprotected civilians stood near impact sites. In the aftermath of the August 21, 2013 Sarin attacks in Damascus, multiple videos were posted online showing impact sites, including this one, taken around 36 hours after the attack, showing one of the munitions used in the attack being picked up:

Another impact site was filmed, around 30 hours after the attack, with no apparent ill effects:

In another video, birds that were reportedly killed in the attack are shown several hours after the attack:

Despite attempts by some to claim the presence of civilians at the impact site after the attack indicates that the use of Sarin on April 4, 2017 in Khan Sheikhoun was some how faked it is clear that this is based on either an ignorance of the persistence of Sarin, or willfully ignoring the facts.

Eliot Higgins

Eliot Higgins is the founder of Bellingcat and the Brown Moses Blog. Eliot focuses on the weapons used in the conflict in Syria, and open source investigation tools and techniques.

Join the Bellingcat Mailing List:

Enter your email address to receive a weekly digest of Bellingcat posts, links to open source research articles, and more.


  1. Just Passing Through

    “uploaded over 48 hours after the attack, with no indication it was filmed close to the time of impact”

    The video is probably from late on the 4th – look at the direction of the shadows and the rocks in the road.

    In videos from the 5th something has run over the rocks, you can see them smeared on the road and you can see more clearly how the rocks look on the 6th

    Re. the persistence, journalists who didn’t even arrive until 2 hours later ended up in hospital “Abdurrauf Kantar, who arrived in Idlib’s town of Khan Shaykun on Tuesday a full two hours after the attack, was nevertheless taken to hospital after showing symptoms of gas exposure.”

  2. Sean Lamb

    Some of the witnesses are certainly unreliable and partisan, that doesn’t mean the footage or nature of chemical agent should be disputed.

    You yourself have pointed out the account of Ismail Raslan who claims to have been so close to hear a whoosh of a bomb falling and going out on balcony and yet suffering no ill effects. Immediately running out of the a collapsed boy and experiencing nothing – this is simply a dishonest witness. HRW is even aware he is dishonest, since they selectively edited his testimony to conceal his implausibility. Accounts of “white mist” and “yellow mist” – are these even compatible with the volatility of clear liquid sarin? They sound like drawing on literary descriptions of experiences of mustard gas on the western front of WW1,

    But I don’t think you should extrapolate from the handful of politicized witnesses contaminating the record to dismissing or minimizing the whole incident.

    Efforts are probably better directed at getting the OPCW to disclose if the sarin they disposed of showed any traces of hexamine as a scavenging agent. Which looks like it might be the weak link.

  3. Adam Larson

    Criticisms of the opposition story based on sarin persistence do tend to fail. However, the opposition’s story still fails even worse.

    Adrian D. raises valid points about the inconsistent effects of this supposed sarin fog all over the town, with some passing out with foam instantly, never to wake up, while others (Abdelhamid al-Yousef, for example) can feel the effects in one spot, then run to two other affected areas in town, carry sarin-killed relatives at each site with no protection, and then … pass out for a while at the end, before waking up full of stories.

    Strange sarin indeed is likely to be used in such a strange regime attack: It start with negative motive, as with Ghouta 1, and strong positive motive for terrorists, who can get away with it simply by blaming the other side (a trick that pointedly does not work the other way aroun). Strangely, the US radar track shows the jets never passed over the town to drop any sarin gravity bombs as alleged. So despite the specific claims, it must’ve been done with missiles, and whatever else we have to make up for them. And if they did, manage to hit these spots, of course, the wind is clear in blowing almost exactly away from all the affected people SW of the cited crater. And I acknowledge that crater and its environs were apparently tainted with sarin (or a sarin-like substance), either from whatever hit there, or from an effective later planting. But there was a discernable wind countering the area’s slope (the OPCW chose to ignore the open-source info proving this, but none of us should), pushing whatever was released at the crater to the northeast, away from all those people said to die of sarin to the southwest. So what poison killed them and where it came from remain unclear and unexplained.

    Also, it’s not at all clear the victims really died in their own homes in that area, nor just who they really were. It could be they were laundered hostages killed in one big basement somewhere in town. Sarin doesn’t hack little kids in the head to finish them off, as seems to have happened with some of the victims. This part, if not all of it, must have been done by the local “freedom fighters” with their “Assad did it” conspiracy theory that runs against the evidence.

    But yeah, sarin is non-persistent, and the area can be safely visited within … not sure. Hours, if not minutes. You won’t want to stick an unprotected hand into shaded soil at the bomb site, but breathing the air should be fine. Unclear if the same applies to any other “sari-like substance” it might have actually been. Lesson: many “conspiracy theorists” don’t know how to pick a good argument over a lame one. They should work on that.

  4. Mark

    I think the Syrian Air Force dropped a sarin bomb. I’m also very curious about what happened to the munition. I know the site was not secured and that items could have been added or taken away. But it’s still worth talking about what evidence we do have.

    We’ve all seen the large piece of metal and the round cap. But are these parts of the munition? Most likely, but I don’t think HRW’s claim that they are parts of a Soviet KhAB bomb is credible. And where are they now? The table above seems to say that the Syrian government has the “two metal objects from crater.” The OPCW also states:

    “5.107 The FFM was unable to retrieve any parts that might relate to dispersion of a chemical. However, the FFM was informed that remnants of a munition from the impact crater (point 1 in Figure 5) have been secured and could be made available in the future.”


    “6.19 Although, some witnesses advised that the release was due to a munition dropped from an aircraft, the FFM was unable to retrieve any items from the site which would indicate the means of dispersal of a chemical. After analysing photographs and video supplied by witnesses, the FFM could not establish with a great degree of confidence the means of deployment and dispersal of the chemical.”

    Does this imply that FFM could have secured munition remnants and didn’t? Or that the possessor didn’t want to give them up now? If the remnants are the two pieces of metal, then the SAR likely has them. How did they get them? And why didn’t the locals find and/or keep any remnants to give to the OPCW directly?

    • Adam Larson

      Interesting. Why would rebels leave the telltale scraps for Syria to find?

      Belief in a dropped bomb still runs counter to the radar track. A missile could still be possible, or somehow the track is extremely wrong, showing the wrong location and heading. The FFM wouldn’t want to highlight a contradiction, so they remain mum about whether it was a bomb or a missile. They’d want to say missile, but most have been very clear it was a bomb.

  5. Avryl Densy

    ‘”While open source evidence clearly showed government forces would in fact have been in recently captured territory within the 2-2.5km range Postol and Lloyd proposed for the rockets, Postol continued to promote his theories…”

    You fail to mention that this “recently captured territory” was 2km NE of the impact craters which is what Postol was referring to in his reports. Had government forces launched rockets from this location, as you claim, they would have landed facing SW. Instead the rockets landed facing South. Due North of the impact craters was rebel controlled territory.

    With regards to Khan Sheikhoun, I’ve said it before several times, there is NO evidence of a Sarin bombed let alone an air dropped Sarin bomb. You know this very well Eliot as every time you have been asked to present evidence of your claims you sidestep and launch a tirade of abuse at your challengers. For a person that is persistent on evidence being presented in a debate you seem very willing to ignore your own criteria in the KS debate. You don’t require any evidence to conclude it was an air dropped Sarin bomb. That’s “truther” stuff right there.

    Until the Khan Sheikhoun truthers offer up any evidence to support their claims of a big bomb, filled with Sarin and dropped from a Syrian fighter jet then their claims will be filled under “Conspiracy Theories”.

    • Adam Larson

      On the Ghouta rockets:
      1) the problem with Higgins’ conquered areas is they’re all as of Aug. 24, 3 days later. He seems to presume it was the same early on the 21st.
      2) detailed analysis is just now showing the north firing spot picture is erred; maybe some came that way, but mainly it’s more northwest (see Michael Kobs on Twitter, Impact Site #4 on Monitor on Massacre Marketing)
      3) big leap; these might have been fired from a government-held area by the government or allies. I know sarin turned up at the sites a week later, but it was probably planted; that’s a long time to last, and the signs are these rockets unleashed fuel-air explosions, which would destroy any sarin they had. (See Talk:Thermobaric Weapons at A Closer Look On Syria.) Suggested: they had nothing to do with any chemical attack, were just part of the general offensive in the area, and were just used as props later, and tainted with sarin later yet. The fatal victims (who were never tested or sampled) were probably gassed with other things in a number of basement-level gas chambers. Something noxious may have been released in the air as an effect, but it probably didn’t kill anyone, or come from these rockets.
      4) But maybe they did release the/a chemical, in which case government territory is unlikely, as they weren’t the ones with a motive.

    • Azriel

      Avryl Densy.

      Do yourself a favor.

      First, look what the Russians/Syrians said. Second, find out they said that they striked a jihadi compound with chemicals which led to the casualties. Thirdly, find me the coordinates or photos of the alleged spot.

      By failing to do so you prove that the syrians/russians are lying about what happened 4th august in Khan Sheikoun.

      Either you’re intentionally misleading to back up Assad for your own ideological/political reasons, or you have a serious mental defect. It must be one of them considering you’re not understanding the impliciations of what l mentioned above.

      • Sean Lamb

        Azriel, you certainly have a point the Russians are not very intelligent – except apparently when they are hacking elections when they are mind-bending Svengalis.

        They have got it into their heads (correctly) that the West are engaged in informational warfare and they have to respond in kind. Unfortunately the West control the commanding heights in this campaign of informational warfare and to defeat them it is not enough to come up with any alternative explanation – they have to come up with a better alternative explanation, one that is as close to truth as possible.

        The Russians haven’t got this yet, they think it is acceptable to just say anything on the grounds the West is lying through their teeth, so why can’t we?

      • Avryl Densy

        “By failing to do so you prove that the syrians/russians are lying about what happened 4th august in Khan Sheikoun.”

        You have the burden of proof the wrong way around my friend. You see it isn’t I that is making the claim of a big massive Sarin bomb dropped from a Syrian fighter jet. Therefore it isn’t up to me to disprove a negative by proving it didn’t happen. It is, rather, up to those proponents of such a conspiratorial narrative to prove their case. They haven’t. Not one ‘air dropped Sarin bomb’ flag flyer has provided a shred of evidence to support their claim. None.

        I care not what the Americans, Russians, Syrians or crazed up Jihadists say on the matter. I care only for the facts. The evidence. Where is it? Where’s the bomb?

        “Either you’re intentionally misleading to back up Assad for your own ideological/political reasons, or you have a serious mental defect.”

        It’s always the same with conspiracy theorists. When you are challenged on your evidence (or lack of) you adopt a defensive position and personally attack those asking the questions. That script is a bit tired don’t you think?

        Where did you say that Sarin bomb was again?

        “It must be one of them considering you’re not understanding the impliciations of what l mentioned above.”

        Yes. I must have a mental defect because I refuse to just believe what I’m told without the need to see evidence.

        Come back to me when you’ve any evidence of your conspiracy theory of a magical Sarin air dropped bomb that literally vanishes upon impact never to be seen again. But before vanishing, mutates into the remnants of an odd looking metal fragment thing then when the world laughed at it……puff, it’s gone too. What ever happened to that HRW claimed OFAB???

        Ask Eliot can you can borrow one his tin foil hats he used in the graphic in the earlier thread.


Leave a Reply

  • (will not be published)

You can support the work of Bellingcat by donating through the following link: