The testimony on Wednesday will be accompanied by a dossier of evidence compiled by the Syrian American Medical Society (Sams), a charity that runs 95 medical facilities inside the country. It documents 31 separate chlorine attacks between 16 March and 9 June. The charity says all the attacks were conducted by launching barrel bombs from helicopters and many targeted civilian areas, leaving 10 dead and at least 530 people seeking medical treatment.
The dossier, which has been seen by the Guardian, provides US lawmakers with data, photos and videos that Sams says were taken in the aftermath of chlorine bombings in a province of Syria recently overrun by militants, including the al-Qaida-affiliated al-Nusra Front.
The Guardian has been unable to verify the material, which includes videos and photos of adults and children struggling to breathe, often wearing oxygen masks. Some are retching, while others are being stripped and hosed down to remove chemical residue.
Sams also provided the Guardian with a redacted list of basic patient information for 221 people treated for chlorine exposure. According to that list, 57 were under 18.
The lead medical coordinator for Sams in Idlib province, Dr Mohamed Tennari, has flown to Washington DC and has been invited to testify in front of the House foreign affairs committee on Wednesday morning. Tennari will say that although chlorine is less likely to kill than conventional weapons, it has created a “new type of psychological torture” for the Syrian people. He told the Guardian: “We would like to see a no-fly zone and increasing help being provided to refugees.”
The Sams data only reflects attacks that have been confirmed by the charity’s own facilities, and only those taking place in Idlib province. Other activists, including the White Helmets, a volunteer rescue service who will also testify at the hearing, have reported further incidents in the adjoining Hama province.
Recent reports suggest that militant forces in Syria, including Isis, are developing a chemical weapons capability of their own. Isis are understood to have used chlorine in Iraq. However, Sams said that all the attacks in their data were launched from helicopters, which are only operated by the Assad regime.
The Syrian president has denied that his forces have deployed chlorine. Although the chemical is widely available, its weaponisation is strictly banned under international law. In an interview with France 2 on 20 April, Assad said there was no proof of chlorine use in attacks on Idlib city.
“This is another fake narrative by the western governments … The regular armaments that we have are more influential than chlorine, so we don’t need it anyway,” he said. “We didn’t use it. We don’t need to use it. We have our regular armaments, and we could achieve our goals without it. So, we don’t use it. No, there’s no proof.”
Tennari, who set up a field hospital in Sarmin four years ago, will tell US lawmakers that the vast majority of chlorine attacks identified by Sams occur at night. The barrels do not explode. Instead the vapour seeps silently into houses and sinks down into basements where residents are likely to be sheltering from conventional explosives. There the toxic gas can choke its victims as it reacts inside the lungs to produce liquid hydrochloric acid.
Tennari told the Guardian that chlorine attacks were being used by the Assad regime to push people out of areas it no longer controlled. “This is a form of collective punishment by the government,” he is expected to tell US lawmakers.
He will describe chaotic scenes following the first and largest attack recorded in the dossier, which took place on 16 March, as scores of patients had to be treated with atropine and oxygen. Shortly before the attack, he says he heard helicopters.
“An announcement blared through my walkie-talkie and through mosque speakers of Sarmin that explosive barrel bombs had been dropped. They said that the barrels were filled with poisonous gas; it was a chemical attack.”
As he left his house to head to the hospital, he could smell bleach. “When I arrived at the hospital, a wave of people had already begun to arrive. They were all experiencing symptoms of exposure to a choking agent like chlorine gas. Everyone was decontaminated with water before coming into the hospital, and their clothes were taken off of them. Dozens of people had difficulty breathing, with their eyes and throats burning, and many began secreting [fluid] from the mouth.”
He said as he treated those victims, helicopters dropped two further chlorine-filled barrels. Sams reports chlorine bombs landing in both Sarmin and Qaminas that night, leaving 120 people needing treatment.
The hospital also recorded that Waref Taleb, a local electrician, was killed along with his wife, 65-year-old mother and three young children when one barrel exploded in their home.
Human Rights Watch independently investigated this attack and corroborated these findings. It reported that 30 civilians and 40 rebel fighters were affected in the Qaminas attack alone.
Chemical weapons expert Hamish de Bretton-Gordon said he and others working alongside him in Syria had separately confirmed chlorine use from samples taken from the destroyed Taleb family home on 16 March.
“I have absolutely no doubt, it was chlorine,” he said. “It smelt like chlorine, it looked like chlorine and three different tests said it was chlorine.”
He added that although chlorine wasn’t itself considered to be a particularly toxic chemical of war, its psychological impact was devastating.
“People I know and speak to in Syria are still absolutely terrified by chlorine. I tell them that it is not really that poisonous, but their line is always that ‘we can hide from bombs and bullets … but we can’t hide from gas’. And that psychological weapon is I think the key thing why Assad still uses it.”
In recent months there has been increasing momentum within the international community to tackle the issue of chemical weapons use in Syria.
On 6 March, the UN security council passed a resolution condemning the use of chlorine as a weapon and threatening action, including possible military action, if such attacks occurred. But it is not clear what steps the security council will take if the regime is found in breach.
Although the international body for monitoring chemical weapons, the Organisation for the Prohibition of Chemical Weapons (OPCW), is understood to be investigating this latest alleged spate of chlorine attacks, its current mandate from the UN does not allow it to assign blame for such attacks.
However, speaking from Camp David a month ago, the US president, Barack Obama, said if the US itself managed to confirm further chlorine use it would “once again work with the international community” and “reach out to patrons of Assad like Russia to put a stop to it”.
Additional reporting by Joe Evans