There have been a number of news reports over the weekend about the possible use of chemical weapons by Syrian opposition forces. Nothing has yet been confirmed by independent investigators, but most news reports concern the use of a single round of undetermined size that contained some sort of chlorine based chemical.
The third hand descriptions do not sound like chlorine gas, but rather some sort of chlorine bleach based munition. This does not make a lot of sense on a number of levels. While chlorine bleach (sodium hypochlorite) is a corrosive when dissolved in water, significant amounts would have to be splashed on someone to cause militarily significant wounds. Highly concentrated bleach does readily decompose to give off chlorine gas, but the amounts present in a single artillery warhead would not produce enough chlorine gas to be lethal or even incapacitating in all but the most limited confined area.
To have an improvised chemical munition that could be delivered by tube or even rocket artillery requires a shell that is designed to be filled with a liquid, and can withstand the shock of launch without leaking. It must also be equipped with a burster charge and fuse combination that will make it detonate and disperse the chemical agent upon impact. Finally the whole thing must be properly balanced and weighed so that the flight characteristics will produce an adequate level of accuracy to allow delivery to the target area. This is not something that can be whipped up in a casual machine shop.
Syria probably has significant stocks of properly constructed chemical weapon shells waiting to be filled; they reportedly have a significant chemical weapons capability and inventory. Rebels may have gotten their hands on some quantity of these empty shells. They may even have been able to buy such shells on the black market from the defunct weapons programs in Libya or Iraq or any number of old Soviet bloc countries.
If they had access to the empty chemical munitions, it makes no sense for them to fill even one of their almost certainly limited supply with bleach since it is such an ineffective chemical weapon. If one were going for just the contact corrosive effect there are any number of commercially available corrosives which would have produced much nastier chemical burns. If they were going for a toxic effect, there are other more lethal industrial chemicals or pesticides which would have been more effective.
What is much more likely is that a conventional artillery shell hit a storage container containing bleach. Sodium hypochlorite in concentrations as high at 60% is a fairly common chemical in a number of industrial operations and is used as a disinfectant in drinking water systems and many cooling systems. Breaching an industrial scale bleach storage tank would produce a chemical effect over a much larger area than a single chemical shell.
This is one of the problems with conducting military operations on urbanized terrain (MOUT the then current term when I last professionally studied the subject low many years ago). Industrial areas contain storage containers of various sizes of nasty chemicals. When an artillery round or even a rocket propelled grenade punctures such a container, the chemical is released into the environment. The tactical effects may be virtually indistinguishable from a chemical attack.
On a strategic level politicians have to be very careful to ensure that they can distinguish between accidentally released industrial chemicals and the deliberate attack with chemical munitions. While both may cause death and disfigurement to innocent civilians the latter may require a formal military response while the former may just merit a call for a cease fire to allow the dead and wounded to be evacuated and treated.
The situation calls for a very careful and thorough investigation by people who know their business. I am glad to hear that the OPCW has been brought into the process by the UN.