of volunteers in the northern city of Aleppo.
"If it's a sarin attack, you need to open the windows to ventilate the houses. It's a very lethal gas but it disperses quickly."
"VX is more dangerous. We cannot take off the protective clothing at any time because it penetrates the body not only through our respiratory system but also through the skin and eyes," says Zayed.
Sarin is a paralysing, odourless agent that can kill in minutes and was developed by Nazi scientists in 1938.
Several Western countries and Syrian opposition groups say the regime used it in the rebel-held areas of Eastern Ghouta and Moadamiyet al-Sham in the outskirts of Damascus on August 21.
VX is an even more deadly derivative of sarin, while mustard gas causes suffocation and severe burning of the eyes and respiratory system.
The United States says there are some 45 sites in Syria linked to the regime's chemical arms programme.
Washington agreed with Moscow on Saturday that Damascus' chemical arsenal will be identified, inspected, handed over to international supervision and destroyed by mid-2014.
But after the alleged chemical strikes that are said to have killed hundreds, fears in rebel-held areas that they too might be hit are running high.
For two months, Zayed has been training a group of 26 civilians in the hope they can respond to another such attack.
His students include ex-firefighters, students, welders and heavy machinery drivers.
"If the regime uses chemical arms to attack Aleppo city tomorrow, we will be ready to act and help the civilians," Zayed says.
"They (the regime) won't think twice before they use (chemical arms) against the civilian population, only to then blame the rebels for the attack," he added.
Damascus and Moscow have flatly denied Assad's regime had any part in the alleged chemical attacks near Damascus.
They say the rebels staged the attack to try to provoke international intervention.
But 45-year-old Abdel Moneim, who leads this unusual civil defence team, is convinced Assad is responsible.
"What happened in Ghouta is the work of Assad's regime. If the rebels had chemical weapons, the war would have been over months ago. In any case, they would never use them against the civilian population," he says.
Like Zayed, Abdel Moneim believes the government might use chemicals to target Aleppo, large swathes of which fell out of army control after rebels staged a massive onslaught in July last year.
"Bashar al-Assad would not hesitate to use chemical weapons against Aleppo. And he will accuse the rebels of staging the attack," he said.
Despite their rudimentary methods, Zayed and Abdel Moneim have full trust in their team.
But their main problem is they only have 24 protective suits, which they obtained during a rebel attack against a loyalist army base, and just three gas masks.
"Without masks we won't be able to do much for people, because even a moist handkerchief to cover the nose and mouth won't stop the chemical agents," said Zayed.
Still, he thinks it is "very important that more groups like ours are set up in the country, to help the civilians. We know our limits but we will try to save as many lives as possible."
"Otherwise, people will die like they did in Ghouta," said Zayed.
In a school in the New Aleppo district of Syria's second city, two of Zayed's students volunteer to participate in an evacuation drill.
They don protective gear and masks, and move down to the courtyard.
A student lies down on the ground and plays at being the victim, while Abdel Moneim calls out instructions.
Meeting every day for class, "the students are trained in first aid to help civilians in case of an attack," says Abdel Moneim.
"Our team will follow instructions of medical workers at the Zarzur hospital, which will be tasked with receiving patients in case of a chemical attack," he adds.
The volunteers have started distributing leaflets to Aleppo residents, explaining how to react to an attack, and how to "hold on until the rescue team arrives," says Zayed.
Although Damascus has agreed to hand over its arsenal, residents of Aleppo's rebel districts are still on guard.