With only a cloth mask for protection, Firas Kayali rushed to try to rescue the residents of a house in a village in rebel-held northern Syria after a barrel bomb, suspected to be filled with chlorine gas, hit nearby.
Once a house painter and now a member in a volunteer rescue team, Kayali tried once, twice, three times to break into the house, but he was overcome by the gas and passed out. Only 20 minutes later, after the gas dissipated, was the team able to get into the house.
Inside, they found a toddler dead, still wrapped in his blankets in bed, Kayali told The Associated Press, recounting the May 2 attack.
The child's father died a few days later, his lungs collapsed, in a hospital near the Turkish border.
"I blamed myself first. But then again I go back and say if we had equipment and outfits, maybe," Kayali said. "Then again, 'if' will not change anything now. ... God destined and what he destined happened."
Frustrated and despairing, Syrian opposition activists are trying to garner international pressure to stop a growing number of attacks using chlorine gas, which they say are undoubtedly carried out by government aircraft.
Two years after President Bashar Assad agreed to destroy his chemical arsenal and joined the Chemical Weapons Convention, activists say they have documented 18 cases of chlorine gas used in the country's rebel-held north since March 6, when the United Nations issued a resolution determining that chlorine was used in Syria and warning of repercussions.
They say the attacks have killed nine people and injured hundreds.
The Syrian government denies using chlorine gas. But activists and residents of the villages hit say the attacks, usually at night, are clearly by government forces.
The chlorine bombs are dropped in barrels from the skies, and residents say they hear the buzz of helicopters first.
Syrian military forces are the only combatants in the civil war known to fly helicopters, and the villages hit are pro-rebel, largely in the northwestern province of Idlib.
Still, it is proving impossible to legally link the Assad government to the attacks.
The U.N. agency in charge of determining whether chlorine was used does not have the mandate to assign blame.
The Organization for the Proliferation of Chemical Weapons also can't get to the scenes of suspected attacks without the cooperation of the Syrian government, while testimonies or evidence collected by people on the ground are considered circumstantial.
The U.N. Security Council is paralyzed because Russia, a major ally of Assad, insists the allegations are "propaganda."
The Syrian Civil Defense, a group of 2,640 volunteers that provides emergency and rescue services in rebel-held and contested areas, has been gathering evidence to document the recent attacks, said Farouq Habib, the group's political adviser.
He and the group's director, Raed Saleh, returned this week from the United States, where they met U.S. and European officials.
They collected remains from the barrels used in a number of bombings, soil samples that the group says show high levels of chlorine traces and urine and blood samples from victims.
"The samples are valuable for the Syrian people because they document the crimes committed against it," Habib said in a telephone interview. "It is there and documented and saved but will only be presented after putting together a legal case that guarantees it is used in an effective way to indict the criminal who used chlorine against the Syrian people."
Habib said his group has offered the OCPW to either take the samples in a handover over the border with Turkey or to host its staffers on visits of areas of suspected attacks.
Deliberations are underway over a U.S. proposal to set up a parallel commission of inquiry that would be mandated to determine blame.
Details of the proposal have not yet been made public, but Saleh said the new commission is likely to face the same obstacles.
For example, he said, only those who reach the scene of an attack immediately would be able to document a case. "We all know the gas effect doesn't last for more than a few hours," he said.
That's one reason, experts say, Assad continues to use the gas.
When used with the intent to hurt or kill, chlorine is considered a chemical weapon, but chlorine itself, used for industrial or domestic purposes, is not included in a state's declaration of chemical weapons.
"The regime thinks that if there were documentations of samples contaminated with chlorine gas, it can claim it is in homes or that anyone has used it," Habib said.
Government officials last year accused the militant group Nusra Front of detonating containers with chlorine, but offered no proof.
Kelsey Davenport, the director of nonproliferation policy at the Washington-based advocacy group Arms Control Association, said that while the use of helicopters points to Assad's government, negotiating access for a formal investigation with a mandate to assign blame is difficult.
"If a designated body has the authority to determine who is responsible for the chlorine attacks, the Assad regime is unlikely to cooperate, or provide security assurances," Davenport said.
Speaking to reporters, U.S. President Barack Obama said last week that his administration will work with the international community to investigate the claims but has stayed clear of threatening action.
Obama threatened military strikes after 2013 sarin gas attacks blamed on Assad in Damascus suburbs that killed hundreds, but later backed off amid a Russian deal that saw Assad agree to destroy his chemical weapons.
Saleh and other Syrian opposition figures are campaigning for a no-fly zone, or safe zones, to protect the civilians against future attacks.
But over the course of the 4-year-old civil war, there's been no appetite in the U.S. or its allies to enforce such a zone.
Kayali, the medic, said even precautions taken by civilians to avoid government bombing have become lethal.
"People used to think that by digging underground vaults that they would be safe," he said. But he said a recent attack that killed six saw a barrel land in the ventilation shaft of a bomb shelter.
"We will end up dying one by one, and no one is aware of us," he said.