The Sarin attack in August 2013 and the subsequent UN report have raised many questions about culpability for the attack. I have long stated that I believe the evidence is stronger that this was an attack by pro-govt forces rather than rebel forces based on a number of reasons. I still believe that to be true, but I want to address the issue of hexamine, as some believe it is evidence of Syrian army culpability, while others believe it points in the opposition direction.
Hexamine was found by the UN in numerous samples in its analysis of several rockets used in the attack. Hexamine was also declared by the Syrian government as part of its chemical weapons program. Hexamine was allegedly as a so-called “acid scavenger” in the Sarin process, to bind to the hydrogen fluoride produced in mixing the chemicals that form Sarin. Because hexamine was found on the ordinance used in the attack, and hexamine was declared by Syria as a chemical used in its chemical weapons program, it has been theorized that hexamine is a “smoking gun” that points to the Syrian army culpability in the attack.
Hexamine, in addition to its use as an acid scavenger in the Syrian chemical weapons program, is a chemical reagent used in the production of three explosives: RDX, HMTD and HMX. RDX is the most common explosive used by militaries in the world. RDX can be made by different processes, but the Bachmann process, which uses hexamine, is the most common. In this process, hexamine is nitrated in the presence of ammonium nitrate.
HTMD has been used in many terrorist attacks in the world, including the 2005 London bombings. RDX has similarly been used in many terrorist bombings, which is unsurprising given its ubiquity. Wikipedia says for example it was the main component used for the 2006 Mumbai train bombings, the Jaipur bombings in 2008, the 1999 Russian apartment bombings, the 2004 Russian aircraft bombings, the 2010 Moscow Metro bombings, and the assassination of Lebanese PM Hariri in 2005. Without confirming this, I have no reason to doubt it – RDX is very common explosive. It was widely reported in the US media that US Army soldiers in 2004 guarding an “Al-Qaeda” facility in Iraq were overrun by looters. One soldier saw looters carrying out bags of a substance called Hexamine, which the soldiers did not know the significance of at the time. Later they read of its role in the production of explosives.
HMTD is an explosive made from hexamine and hydrogen peroxide in the presence of citric acid. It is a very unstable explosive. It has been used by terrorists but it is unlikely to be used as the detonator in the rockets used in the Syrian Sarin attack. RDX, however, would be the top candidate for use as the explosive material in the rocket.
Given hexamine’s use as a precursor or reagent in these explosives, it did not surprise me that hexamine was detected by the UN laboratories. I located a paper titled, “Mass spectrometry analysis of hexamethylene triperoxide diamine by its decomposition products”, by Alvaro J. Peña-Quevedo; Samuel P. Hernández-Rivera, published in SPIE Proceedings Vol. 7303 Detection and Sensing of Mines, Explosive Objects, and Obscured Targets XIV, Russell S. Harmon; J. Thomas Broach; John H. Holloway, Jr., Editors, 730303. The abstract is here: http://spie.org/x648.html?product_id=819080.
The abstract reads, “Hexamethylene triperoxide diamine (HMTD) is a well known amine peroxide that starts to decompose at ambient temperature. At 40°C HMTD began to break up into volatile pungent compounds, including trimethyl amine. The production of these compounds could be useful for the vapor detection of HMTD by common techniques such as GC-MS and IMS. GC-MS analysis was performed and several volatile amines could be detected including initial reagents, such as hexamine.”
This is not surprising. I could not find a similar analysis of RDX, but it seems very likely that if RDX was formed by the most common Bachmann process, then hexamine would be detectable by GC-MS (used by the chemical weapon investigators in Syria) as well as an initial reagent. Therefore, the detection of hexamine on the rockets is not remarkable given that hexamine was was very likely used as an initial reagent in the explosive. The New York Times article on this topic pointed to experts that hinted that the hexamine found could be linked to the explosives rather than its use as an acid scavenger.
UPDATE: After the publication of this blog post on February 15, 2014, Professor Ake Sellstrom, the head of the UN team that investigated the Syria chemical weapon attack, gave an interview to Aron Lund that can be found here. http://carnegie-mec.org/diwan/54863?lang=en
The interview is a must-read. In it, Sellstrom provides reasonable answers to tough question about the attack. Sellstrom acknowledges the point above about heximine, saying: “Hexamine could be a stabilizer of sarin, but others have claimed that the hexamine found could also be a contaminant being present because of the explosives.”
As to culpability for the attack, Sellstrom said that he could not conclude culpability: “We do not have the evidence to say who did what, but on the other hand, we do not have the evidence to say that it could not have been done by this or that party.”