BEIRUT: As the Syrian government and the rebel opposition trade blame over who perpetrated an alleged chemical weapons attack outside Aleppo Tuesday, the question of just which chemical agent reportedly killed 25 people and wounded dozens more remains unanswered.

As one of eight states not party to the Chemical Weapons Convention, Syria’s stockpiles have never been subject to outside inspection, but the state is believed to possess significant quantities of mustard gas and a range of nerve agents, including sarin. It is also known to have missiles, artillery shells and short-range rockets capable of carrying chemical warheads.

However, initial speculation following Tuesday’s alleged attack, which Western powers have not confirmed, suggests neither sarin nor mustard gas were used in the incident.

Mustard gas, a blistering agent, incapacitates its victims by irritating the skin. It can cause permanent damage if inhaled, although it is less lethal than other chemical weapons and doesn’t usually result in immediate fatalities. Sarin, a nerve agent, is far more lethal. When inhaled, it works rapidly to paralyze the muscles near the lungs, causing victims to suffocate.

Initial witness reports Tuesday said victims had difficulty breathing and were treated with IV drips and oxygen. Their skin appeared unblemished. Some reported smelling chlorine.

Such accounts appear to suggest that a choking agent could have been used, said Patricia Lewis, research director of international security at the British think tank Chatham House.

The apparent lack of blistering on victims’ skin indicates it is not mustard gas, while the use of sarin, which Lewis reiterated Syria is believed to possess, would also result in a completely different set of symptoms.

“Choking could mean a number of things, including chlorine,” Lewis told The Daily Star.

It is very possible the Syrian regime possesses chlorine, a gas initially used during World War I. “It’s an old gas,” Lewis said. “It’s certainly within Syria’s reach to have it.”

She added that it was much less likely that the opposition would have chlorine among its weapons stockpile, noting that the agent would have to be produced on an industrial scale. Lewis noted, however, that it might be possible the rebels captured chlorine-loaded shells from a weapons depot.

Eliot Higgins, a contributor to the Brown Moses Blog, which documents military hardware and tactics used in the Arab revolts, questioned “which weapon in the Syrian army’s inventory uses chlorine-based warheads?”

He was “pretty sure” none would.

“If chlorine gas was used, the amount needed to inflict that number of casualties would likely be very high,” Higgins pointed out.

“There’s no way the DIY [homemade] rockets used by the opposition could deliver that volume of gas, and the government has claimed the missile or rocket used was fired from 30 km away, which seems well beyond the rebels’ DIY rocket-making capabilities,” he said.

“If it was chlorine poisoning, I get the impression it’s more likely something that was hit on the ground leaking gas than a chlorine warhead,” Higgins added, noting that if a large missile or rocket were used there would likely be plenty of debris for the state to show off.

However, he reiterated the lack of information presently available for analysts like him to work from: “What would also be useful is knowing the exact location of the attack, and footage from the scene of the attack.”

Lewis also emphasized the scant information available alongside the multitude of variables impacting the outcome of a chemical weapons attack. The quantity of chemical released must be combined with the weather conditions and the exact nature of the location – whether a valley or a hilltop, for example – to determine the extent and degree of impact.

With this in mind, Lewis recalled the December suspicions – revealed in a leaked Obama administration cable – that the Syrian regime used BZ, a chemical agent similar to Agent 15 which is banned in war but not for crowd control.

Depending on the exact circumstances, she said, it cannot be ruled out that this agent, which causes respiratory problems among other symptoms, could have been used. – With Agencies