Rod Barton was a senior UN weapons inspector in Iraq. He is the author of The Weapons Detective: The Inside Story of Australia's Top Weapons Inspector.

It is difficult from media reporting to sort fact from fiction about allegations of chemical weapons use in Syria. The chaos of war and the desire of both sides to demonise the opposition while painting themselves in the best possible light only adds to the confusion. However, even though there can be no certainties at this stage, a careful study of the media combined with an understanding of chemical weapons and the Syrian crisis enables the development of some ideas of who may be behind the alleged attacks, what sort of weapons might have been used and why anyone would resort to the use chemical warfare in this conflict.

The who

Some commentators have questioned whether the reported chemical attacks are authentic, and until the UN team in Syria has investigated the claims, there is likely to be continuing doubt. But rebel video images of victims from the latest alleged attacks in the Damascus eastern district of Ghouta on 21 August provide compelling evidence that chemical weapons were used. This is supported by independent reporting such as that from Medecins Sans Frontieres. Assuming that chemicals were used, the questions arise as to who conducted these attacks and under what authority.

The Syrian Minister of Information and others have accused the rebels of using chemicals against their own people. The rebels, they claim, have then blamed it on the Syrian Government to engender international sympathy and draw the US in to the conflict.

While it is difficult to completely understand any conflict from a rebel's point of view, it would seem that any advantage the rebels may gain from such a strategy would be far outweighed by the downside. Firstly, it is difficult to imagine the rebels callously killing possibly hundreds of their own supporters for a dubious and uncertain gain. And whether the rebels would have the technical expertise to conduct such an attack, even if they possessed captured government chemical weapons, is also questionable. Furthermore, the rebels controlled the area of the attack in Ghouta and used it to block an entry route into central Damascus; their hold on this front must now be weakened.

So if not the rebels, did the Syrian Government conduct the attack?

Syria probably developed its chemical weapons in the early 1980s and has had three decades to develop concepts of use as well as command-and-control protocols. It is almost certain that any authorisation of the use of chemicals, at least in the first instance, would come from the highest level in government, namely the president. What is most puzzling about the recent attacks is that they occurred only a couple of days after a UN inspection team arrived in Damascus.

It could perhaps be argued that this was deliberate to show the rebels that any means would be used to crush them, that the regime did not fear UN condemnation and that there would be no international intervention to save them. This of course is a high risk strategy and could easily backfire.

There is a possibility that some senior Syrian military officer authorised the use of chemicals on his own initiative. Although little is known about command and control of Syrian chemical weapons it is probable that there is a dedicated chemical corps with exclusive control of such weapons. Any use therefore would likely be under the authority of the commander of this unit, and the actual deployment and firing of the weapons would be by the soldiers from the corps. This would occur in coordination with the regular military units responsible for the sector under attack.

While the use by a rogue chemical corps commander is a clear possibility, it would be a daring officer who would conduct the recent attack when the country is under close international scrutiny with a UN chemical weapons inspection team just a few kilometres away.

Perhaps a more likely scenario is that the recent attacks were an 'accident'. It has been widely reported that. Because of early rebel advances in other parts of the country, chemical weapons have been moved from several storage sites for safe-keeping. It is possible that, in the to and fro of battle, some chemical weapons became mixed up with conventional munitions. Occasionally this occurred in Iraq during the chaos of the Iraq-Iran War.

Although chemical weapons would have distinctive markings, the meaning of such markings would, for security reasons, only be known to chemical corps personnel. Since the munitions themselves would otherwise be indistinguishable from high explosive rounds, they may have been used by the regular army by mistake.

The confusion of conventional munitions with chemical ones would also explain some reports that high explosive rounds were used at the same time as chemical rounds, a practice which would be unusual because it would reduce the effectiveness of the chemical. But it may also be argued that the use of high explosives was intended to break windows and cause disruption, thereby exposing more people to the effect of the chemical.

The what

Syria probably has mustard gas and the nerve gases Sarin and Vx. Vx is technically a difficult compound to make and unless pure is not very stable. Iraq, for example, only made small quantities of this chemical and was never successful in stabilising it. Syria probably has the same difficulties, and if it has produced Vx, it is also likely to be a small quantity. Although there seems to be some anomalies in the symptoms, the gassings in Syria appear to be generally consistent with a nerve gas, but without analysis of samples it is not possible to state what type. Sarin, or an analogue, seem most likely, with the possibility that more than one agent may have been used.

Chemical weapons are most effective if a blanket of gas is laid down over an extended area and this is best achieved by numerous points of release on a windless cool day or at night, as reportedly occurred in Ghouta. The munitions of choice are therefore small artillery rockets, shells, bomblets and spray devices. Syria may have developed any or all of the above munitions.

Of particular interest in this regard is a wide range of artillery rockets of various sizes imported by Syria. Of these, Russian-supplied 122mm rockets, of which Syria has had variants since the start of its chemical weapons program, would be ideally suited. The warheads of such rockets would need to be modified to safely contain the chemical agent; each 122mm rocket would be capable of delivering about 7 litres of agent. A small explosive charge, (a burster), would on impact tear open both the container of chemical and the warhead, and atomise the liquid into small droplets. Sarin droplets and vapour are deadly when absorbed through the skin or inhaled. If such weapons were used, ruptured chemical warheads should be easy to find and would still contain minute traces of chemical. Unlike high explosive warheads, they do not entirely disintegrate.

Syria has several hundred launch trucks (BM21s), each equipped with 40 launch tubes for 122mm rockets. The maximum range of the rockets is 15-20km and with a shotgun-type scatter of perhaps a couple of hundred metres on impact, it makes the weapon system suitable for blanketing an area with chemical. Whether any of these have been assigned to the chemical corps is unknown but the large number of launch tubes on each truck, and the size of the rockets, make them an ideal chemical weapons platform.

If such a system was used against the high density population of Ghouta on 21 August, it is possible just one or two salvos of 40 rockets could have caused the reported casualties. Although several suburbs in Ghouta reported casualties, these are adjacent suburbs and the reporting is insufficiently precise to indicate the actual spread. The reporting is also confused by the possibility that people from surrounding areas entered the attack site to provide assistance and then succumbed to effects of the chemical that contaminated clothing or the environment.

Media reports indicate that the outer suburb of Muadhamiya to the southwest of Damascus was also attacked with chemicals on 21 August. If this is correct then a separate attack must have also occurred.

The why

Some have compared the recent attack in Ghouta with Saddam Hussein's gassing of the Kurdish town of Halabja in 1988, when hundreds of villagers died probably from the nerve gas Sarin. The purpose of that attack was, as part of a wider campaign against a difficult and stubborn opposition, to terrorise and demoralise. The comparison may be appropriate. If the Assad regime used chemicals against the rebel army and their supporters it is probably for a similar reason.

Chemicals also have an advantage in an urban environment in that under certain conditions they can be far more effective than high explosives, as bricks and mortar provide no real shelter against gas. It is with good reason that chemical weapons are classed as Weapons of Mass Destruction.

Photo courtesy of REUTERS/SANA.