Why Chlorine Gas has Returned in Syria and Iraq

At least 13 reported incidents of chlorine use occurred in Iraq in 2006-2007.  Now there are almost daily reports of chlorine being used in the Middle East, whether in helicopter-delivered “barrel bombs” by the Assad regime against civilians or in improvised devices by ISIS or other Islamists of various types. History and science show us that chlorine is not terribly lethal as a chemical weapon, but does have quite useful attributes for attackers, such as the Assad regime and ISIS, fighting in desperate circumstances.

A few years ago, any serious chemical warfare professional would have said that “Peak Chlorine” was a century ago, in December 1915. The major military manuals and textbooks are dismissive of chlorine as a chemical weapon and mention it as being of historic interest and mostly relevant only to industrial accidents today.  The Chemical Weapons Convention (CWC) does not even consider it.  However, after a 100-year hiatus, chlorine lives to fight another day in the Middle East.

Chlorine in the Great War

It is instructive to examine the operational record of chlorine on the battlefield and its physical and technical characteristics.  Chlorine was first used as a weapon in 1915 at Ypres on the Western Front, but contemplation of its military uses began long before Production of chlorine in liquid or gas form dates from the late 1700s. Chlorine weapons were theoretically discussed since 1862, when New York schoolteacher John Doughty suggested it for use in the American Civil War. Chlorine was not the first chemical weapon used in warfare and Ypres was not the first use of chemical weapons; it was merely the first one that anyone took notice of.  There were several other earlier attempts during WWI with other chemical agents, such as tear gases and xylyl bromide, which were completely ineffective and mostly went unnoticed by defenders.

While it did kill and injure people, chlorine was not effective as a lethal battlefield weapon.  Claims that thousands of soldiers were killed by chlorine at Ypres are an exaggeration, as France and Britain only report about 16,000 direct fatalities from chemical warfare between them for the entire war. Instead, the key effect of chlorine use at Ypres was the panic and fear it induced in the trenches. Eventually, effective respirators were developed and fielded, from which point the fear was reduced, only to be replaced with performance degradation. Both of these conditions acted as force multipliers.

A few years ago, chemical warfare professionals would have said “Peak Chlorine” was a century ago, in December 1915. However, after a 100-year hiatus, chlorine lives to fight another day in the Middle East.

Wilfred Owen’s WWI poem Dulce Et Decorum Est captures the visceral fear gas causes:

Gas! Gas! Quick, boys! – An ecstasy of fumbling, Fitting the clumsy helmets just in time; But someone still was yelling out and stumbling, And floundring like a man in fire or lime . . . Dim, through the misty panes and thick green light, As under a green sea, I saw him drowning. In all my dreams, before my helpless sight, He plunges at me, guttering, choking, drowning.

Chlorine was not in use for very long. The reasons were numerous.  In the early days of chemical warfare, attacking troops could not exploit any tactical gains made by an effective chlorine attack, as unprotected troops could not be expected to advance into the cloud that they had just unleashed upon their enemy. Also, the toxicity of chlorine was relatively low, which meant that a lot of chlorine needed to be used in order to have anything close to a lethal effect.  Chlorine lacked an effective means of delivery at any kind of range, as it was not really amenable to dispersal in artillery or mortar shells (some were fielded, but their efficiency was dismal).  The usual way to dispense chlorine on the battlefield was by means of a gas cylinder.

The relatively low lethality combined with the gas cylinder delivery mechanism meant that chemical attacks consisted of thousands of pressurized gas cylinders being hauled, generally by hand, to the front lines. The original Ypres chlorine attack used 5,730 gas cylinders. In several instances, the cumbersome movements of gas cylinders were an obvious indicator to the other side that a chemical attack was imminent.   The advent of better-suited chemicals (such as phosgene, responsible for at least 80% of the war’s chemical agent fatalities and, later, mustard) meant that chlorine was quickly relegated.

Easily-Manufactured Plausible Deniability

Chlorine is not entirely without benefit as a weapon.  It easily manufactured and is available in large quantities as an industrial chemical that will not ring alarm bells with non-proliferation agencies.  Chlorine’s irritant effect might make it usable as an improvised “tear gas” substance, used in riot or crowd control or to drive people from confined spaces. It can also provide deniability for attackers, as the toxic effects of chlorine are relatively non-specific (many other chemicals can cause the same basic signs and symptoms) and post-exposure examination of victims is not likely to conclusively indicate that chlorine was the exact culprit.  This makes it harder to point fingers at “whodunit” afterwards, as has been the case with several reported chlorine gas incidents in Syria and Iraq.

The non-persistent nature of chlorine gas means that detecting an attack after the fact is very difficult.  Unless you are there on the spot with the correct equipment to collect a gas sample, proving chlorine use is problematic. The post-exposure environmental indicators are often quite non-specific.  In other words, a positive test for chlorine in some material from the alleged incident scene does not conclusively point to chlorine gas usage, as other sources of chlorination are possible.

Poor Detective Work

In a video by The Telegraph in April 2014, Syrian soil samples were analyzed by Hamish De Bretton Gordon with a hand-held Dräger gas detector. This particular exercise was touted in the media as proof that both chlorine and ammonia had been used in Syria.  While chlorine may indeed have been used in the particular incident that Mr. De Bretton Gordon investigated, his exercise with a Dräger gas detector and plastic bags do not constitute proof.  Indeed, the conclusion is problematic.  It is my opinion that the ammonia allegation is unsupportable.

Chlorine and ammonia are highly reactive when put together.  How would such an attack possibly have worked in practice?  His particular Dräger detector has published cross-sensitivities for ammonia and chlorine (chlorine gives a very strong response on the ammonia sensor, and ammonia gives a mild response on the chlorine sensor.)  So, claiming both based on the same reading is misleading and shows a fundamental misunderstanding of the equipment.  The soil sample could easily have been chlorinated by some other means.  But would a soil sample doctored with bleach or water from, say, a swimming pool create the same effect?  Possibly. Even a plastic bag in the hot sun can give off traces of chlorine depending upon the kind of plastic it was made of.

Chlorine in Syria and Iraq

So, what is going on with the chlorine in Iraq and Syria? Despite the questionable methods used above, there is a strong circumstantial case that chlorine is indeed being used.  In the various incidents where chlorine was reportedly used, it is actually difficult to point to many victims who died from chlorine exposure rather than from other means, such as fragmentation injuries or other traumas.  Why use such an ineffective weapon? I have four hypotheses, none of which are mutually exclusive:

  • The chlorine may be meant to maim, not to kill, by causing widespread lung, skin, and eye injuries that are painful, but not often lethal;
  • It could be used like a riot control agent (like CS) to force people outdoors from shelters, bunkers, and buildings, making them more vulnerable to conventional attack;
  • It could be used as an attempt to stretch existing conventional weapon stocks due to the degraded industrial base and supply chain.  For example, perhaps chlorine gas is being mixed into barrel bombs in order to conserve explosives;
  • It could be used as a weapon deliberately to induce fear and terror in a target populace fairly well-habituated to conventional attack after years of war.

As the history of chlorine gas use in WWI above shows us, all of the above may be true and they are consistent with how chlorine has been used in the past.  But the last one is the most important one.  People are afraid of poisonous gases.

Syrians are familiar with the use of a lethal nerve agent in the controversial Ghouta attacks and Iraqis know it from Saddam’s use of chemical weapons against Kurds at Halabja and during the Iran-Iraq War. Most people have heard of chlorine and know its smell from household use. This smell, following an attack of some kind, induces fear and fear is an important force multiplier for the chlorine attacker. It makes victims breathe faster, further increasing the intake of the gas and increasing the onset of its effects. The fear and panic caused and ensuing behavior by victims increases the likelihood of injuries from conventional attacks.

Chlorine has a long history of violence. We need to be mindful of its shortcomings, however, and not turn it into something that it isnt. If we make it out to be a highly lethal bugbear, we only serve to increase its usefulness as a weapon by stoking fear. Though it is rather ineffective in and of itself, it does have properties which would make it attractive to users such as the Assad regime and terrorist groups such as ISIS. The fear that the use of chlorine gas induces into populations which, though battle-hardened against daily conventional bombings, are conditioned by their own history to fear chemical attacks is why we are seeing a revival of the use of chlorine as a chemical weapon in war.

[Photo: Flickr CC: Library and Archives Canada]



  1. Johnny Boy 15 April, 2015 at 11:15 Reply

    I read this hoping to find something new but all I discovered was text copied from WW1 Books, notes and statements. I find it intriguing that he says BGs investigation was flawed when it was more of an investigation conducted by any organisation, whilst I am sure he would have loved to fly in a GC/MS, IR etc etc he wouldn’t have been able to get it in the country. Far too often we hear from these armchair experts with opinions on what has been done but don’t actually stick their own heads about the parapet offering any real advice, solutions or offers of help. I would recommend Mr K get off his backside and do some real good.

    • Dan Kaszeta 16 April, 2015 at 09:40 Reply

      Dear Johnny Boy:

      Thank you for reading my column.

      Let me see if I can understand the essence of your complaint:

      1. My opinion column is somehow plagiarised.
      2. Somehow a Drager Miniwarn was the best instrument for the job available at the time, and therefore something was better than nothing.
      3. A GC/MS, if available, would be able to backward calculate the means by which a bit of soil had gotten chlorinated.
      4. Somehow I am an armchair expert, despite my service as an officer in the US Army Chemical Corps and my extensive field work in US government service.
      5. Whatever it is I am doing (which is more than writing columns in Cicero) isn’t “real good”.

      Have I gotten to the heart of it, or have I missed something? Because I can address points 1 to 5 in extensive detail.

      Thank you,


  2. Johnny Boy 16 April, 2015 at 11:11 Reply

    Drager Miniwarn is not the best tool for the job but it’s better tool than nothing (Which is what I would suggest you offer). The Soil was collected as I understand it collected by reputable personnel. War Zones are dangerous places, Perhaps you would like to do it, I understand whilst the majority of our Forces were deployed you were making coffee for the Security Services and are yet to see or experience War.
    Tell us then, was chlorine used (Y/N), by Who, When, Who, How much……difficult isn’t it.

    • Dan Kaszeta 17 April, 2015 at 08:38 Reply

      I will place the ad hominem personal attack on my CV (I have no idea if you read it or not) and the insinuation that my career somehow was that of barista aside. I also know from direct experience that service in a war zone has little or no bearing on how well someone understands and applies the principles of detection and identification of chemical substances… I know a number of guys who are splendid experts on CBRN who have never set foot in a war zone, and I know some alleged CBRN experts with years down-range, and I wouldn’t trust some of them with a spoon, let alone a detection instrument.

      Let me address the fundamental technical points. I don’t doubt it was collected by a reputable person, and I have no information to suggest that the chain of custody was compromised. That’s not the point I make in this case. Also, I will put aside the fact that the MiniWarn is at best the cutting edge of 1997 technology.

      1. Tying the instrument reading to the alleged instrument: You can use a chlorine detection method to determine, roughly and mostly non-quantitatively, that a particular bit of soil has been chlorinated. However, you can’t tell what the source of that chlorine was. The method demonstrated in the video would have similar results from numerous different ways in which the sample may have gained additional chlorine. In other words, the soil sample could have been exposed to chlorine gas, it could have been exposed to another chlorine compound (even a sanitation or laundry chemical), or even in some circumstances have chlorine of a geological nature. The problem is that the method used can’t systematically prove chlorine gas was the source. If we had a sample of the exact same soil pre-incident to use as a reference sample, we could do a before/after comparison. But that’s absurd because we don’t know where these attacks will occur.

      2. Specificity/Cross-sensitivity: I refer you to the Drager Sensor and Portable Instruments Handbook, which I am sure you must have somewhere if you use the MiniWarn. While the chlorine sensor has little cross-sensitivity problem – it is quite specific, the ammonia sensor (see page 181) – has a specific cross sensitivity to chlorine. 10 ppm of chlorine will appear as less than or equal to 20 ppm of ammonia. Therefore, if you are detecting chlorine with the chlorine module AND you also have the ammonia module installed in the MiniWarn, you will likely show a false detection of Ammonia. For the record, hydrogen sulfide, nitrogen dioxide, and other chemicals have strong false responses on the ammonia sensor. The ammonia sensor is highly problematic for this reason. For this specific reason, Mr. de Bretton’s claim of ammonia detection is specious in this instant.

      3. “Better tool than nothing”: No, a poor tool is not better than nothing. That’s patently absurd. Additional data, if it is confusing, ambiguous, or misleading, doesn’t help answer the question. Indeed, if you believe in the “something is better than nothing” school of thought, you are missing a key concept in detection and identification.

      4. Chlorine from plastic bags: I have personally detected chlorine from plastic bags heated in the hot sun. If the storage medium is a possible source of cross-contamination, then the results cannot be relied upon. This can be controlled for by heating a sample of the exact same type of bag, empty, in the same hot sun, to see what kind of reading came from it.

      I’m sure the editors of this magazine will agree with me that we need to keep this technical and professional, rather than an anonymous attack on me. I get enough of that on twitter from lunatics, UKIP “you are a foreigner, we hate you” types, pro-Assad shills, Hezbollah members, and professional paid Putin trolls. Don’t put yourself into the same bin as them, Johnny Boy.

      Have a nice day and stay safe wherever you are.

      Dan Kaszeta
      Safely ensconced in the armchair I earned and paid for.

  3. Armchair Expert 17 April, 2015 at 12:44 Reply

    I am a fully qualified (please note I understand the subject matter – not just how to read a display) armchair expert – who has additionally been deployed on numerous occasions (under fire) but obviously my opinion will not count as it dissents from Johhny Boy’s

    I felt the need to comment here. The assumption that poor intel is better than none is foolish at best, and highly dangerous at worst, as decisions based upon this could potentially lead to fatalities.

    The Telegraph video shows the Miniwarn being used – it is an indicator tool not a confirmatory one – it has, as Mr Kaszeta points out, many cross reactivities (surely an expert would have been aware of this and researched the indication of Ammonia before reporting their findings) . Multiple , orthogonal techniques are used for confirmation – Mr de Bretton Gordon does mention use of litmus as an aside in the video, however, all this will do is confirm acid or base presence – not gas/vapour type but no other confirmation technique.

    None of this would hold up under basic scientific method, let alone a court of law.

    I will not comment upon the collection of samples by non forensically qualified personnel and although mentioned in the video that full chain of evidence was followed, would require more than a reporters word for this, as would any prosecution. Hence I would agree with the statement of ‘Poor detective work’

    Whilst viewing the video I came across a link to the BBC Halabja video. I would suggest this shows misuse of an AP2C, by not allowing it to go through its start up sequence.

    However, the main point is this, again, claims to prove evidence of Mustard gas- ‘three bars of Mustard’, when again, the AP2C has well documented interferents, not least of which are fuels and smoke, and is, yet again, an indicator not a confirmatory tool.

    From memory – the unit would have also quickly cleared down when removed from the source, if it had been working correctly, unless of course there was a high concentration of mustard outside of the basement and both individuals have a natural immunity to it.

    I also believe the unit was actually showing a fault indicator (I am prepared to be corrected, not having a manual to hand). However, not really my point.

    Halabja has been investigated by fully qualified Governmental personnel and NGOs many times showing a cocktail of weapons were used not just mustard – however none of this is really news.

    My own opinion is that much of this is media hype and should be left to duly appointed, fully qualified Agencies such as OPCW, WHO etc to investigate, rather than the media scaremongering that appears to be on the increase, arguably fuelled, in part, by those who could possibly be seen as having ulterior motives based upon their affiliations.

    Mr Kazetas article appears to be factual, accurate and informative which is more than can be said for others.

    • Dan Kaszeta 18 April, 2015 at 10:23 Reply

      Thank you, Mr. “Armchair Expert” for the considered reply. You raise good points about the defensibility (or not) of evidence in judicial proceedings. I couldn’t possibly take a MiniWarn reading into court, for fear of being spatchcocked and humiliated by defense counsel.

      I hadn’t even mentioned the litmus, as it basically proves nothing, and certainly doesn’t count as orthogonal methodology in this particular instance. There certainly are useful things you can do with litmus, but this particular instance isn’t one I would promulgate as a useful example.

      You also raise good points about the AP2C incident, and thanks for providing that illustrative link. Both the video and your commentary raise valuable points of trying to use CWA detection and identification technology for a TV audience, 99.99% of whom will not understand the foibles and subtleties of the devices shown to them.


      Dan K

  4. Hamish de Bretton-Gordon 18 April, 2015 at 16:43 Reply

    You are obviuosly not aware that OPCW confirmed chlorine used at kafr Zita and Talmenes after my so called flawed tests you mention in Nov 14 and with other agencies in possesion of samples tested last week which you also question, we expect similar confirmation, and you appear to disregard the testimony of Ambassador Powell. At HRW, UOSSM and Ambassador Powell we are try to highlight these continuing attrocities to get UNSC action. Myself and all of the above are well used to discention and filibuster from Assad and his supporters, ISIS and its supporters and other ‘nay sayers’ but surprised to hear it from you, and your colleagues. Very happy to give you the full details of the testing and related issues, most of which is confidential in order that you can make an informed comment in future. Very happy to show you some of these places and the people suffering in the van of this battle…I expect it might make you change your mind.
    Hamish DBG OBE

    • Dan Kaszeta 18 April, 2015 at 18:37 Reply

      I don’t doubt that chlorine is being used. In fact I believe much of what you say, just not all of it.

      It is important to read what I said… My specific criticism of your video piece is that I am saying you may well have come to the right conclusion, but the method by which you came to the conclusion is not defensible. What you may or may not have done elsewhere, not on camera is not what I was talking about.



    • Dan Kaszeta 18 April, 2015 at 18:39 Reply

      PS – I am sure that the editors here will be quite glad to publish an article from you. Will put you in touch with them if you so desire.

  5. Susan Dirgham 12 May, 2015 at 00:44 Reply

    Dear Dan,
    Thank you for your article. It is always good to come across expert analysis in regards to the alleged use of chlorine in Syria that doesn’t have a pro-war agenda. Also, it is good to be reminded that it is not unusual for ‘experts’ to disagree and so there must be ongoing discussion and debate rather than a rush to war based on one expert’s opinion.

    I have read Hamish de Bretton-Gordon’s statement above, and I am sure he would label me an “Assad supporter” and so dismiss my comments. The truth is I am an anti-war activist and as such I support honest inquiry. I hope scientists and medical professionals can become more involved in examining the evidence that is used to support war against Syria. However, having said that, I acknowledge how hard it is to stand up against the tide for war. One of my heroes was British scientist David Kelly. His principled stand and his death showed the enormous obstacles faced by professionals who are serious about presenting truths when a government is intent on war.

    In your article, you refer to the alleged chemical attack in Ghouta, Damascus in August 2013. I would like to bring to your attention the report by MIT Professor Theodore Postol and former UN weapons inspector Richard Lloyd. Also, I recommend another report by Dr Denis O’Brien, a retired U.S. pharmacologist. Links to both reports and other analysis can be found on this page: http://australiansforreconciliationinsyria.org/reference-list-chemical-attack-in-damascus-august-2013/

    As for the alleged recent chorine attacks in Syria, there has been discussion on the webpage ‘A Closer Look on Syria’. I believe much of the analysis is presented by ‘experts’. They further challenge Hamish de Bretton-Gordon’s claims.

    Thank you for being prepared to question and challenge in these very difficult times. It seems appropriate to write here that only the truth can set us free.

    (BTW I taught English at the British Council in Damascus for two years, and like virtually all of my colleagues there grew to love Syria – the diversity, the community spirit that existed, the warmth of the people, and Syria’s landscape and culture. There was a positive buzz and hope in the air, though a fear that after Iraq, Syria was next to be targeted for war.)

    Kind regards,


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