They heard two small explosions. One of the men went to open the door to look, and that's when the odor hit them.
"We ran to the roof, we already had gotten information that we should get to high ground if we think a chemical attack has happened," he said. "There was a water tanker, so we started to wash ourselves and cover our faces."
Khattab began vomiting uncontrollably, gasping for air.
His voice cracking with emotion, Khattab described how he clawed at his closing throat as images of others who had perished in past chemical attacks flashed before his eyes.
"I don't want to die, not like this, dear God, please just let me see my children one last time," the 46-year-old recalled thinking to himself just before he fainted.
On February 5, medics and activists reported that a Syrian government helicopter dropped chlorine bombs on the town of Saraqeb, in the northwestern province of Idlib.
Khattab was only in Saraqeb to protect his home from looters, he says. His wife and five children, like most of the others who used to call the town home, had fled days earlier in the face of intensified Russian and regime bombing.
Ali Hajj Hussein and his family were among the few who didn't. He was at home with his pregnant wife and two children when they heard helicopters overhead just after 10 p.m. They heard the sound of something falling, and then the screams began.
"I opened the door and everyone was just shouting 'it's chlorine, it's chlorine.' People were running in all directions," he said. "The smell hit me in the face. It was like smelling bad bleach."
They ran out of the house and jumped into their car. Ali drove his family north, made sure they were safe, and then returned to guard his home. Although none of them were sickened by the bomb, he says the experience was more terrifying than anything he'd been through.
"I feel like death is at our doorstep. We are used to barrel bombs and artillery, but this is something different," he said. "I smelled it, I felt it. This isn't something you can hide from. You have to run, but there is nowhere to run."
The White Helmets, a volunteer rescue group, said three of its members and six others were injured by the alleged chlorine gas attack. The group posted several photos on social media showing men coughing and being put onto stretchers.
Six days after the attack, the field where the two rounds left small craters was silent, save for the distant rumble of explosions and the almost odd-sounding noises of chirping birds. A faint, slightly acrid odor still hung in the air.
Responders from the White Helmets said they arrived at the scene within minutes.
"It was really bad when we got here," 22-year-old Ayham Zeidan, an ambulance driver, recalled. "We put on our masks. We saw the wounded, but there was no blood, nothing. We saw people vomiting."
They had to get to a medical point outside Saraqeb because they said the bombing that night was too intense.
As the ambulance barreled down the road he and his colleague, Rami Dandal, both began to feel affected.
"My entire body started trembling," Dandal said. "I felt like I was screaming 'take off the mask', but no one could hear me -- I was screaming inside my head."
He fainted while they were still en route. Zeidan's body also started to shake.
"I was just praying I would get there," Zeidan remembered. "I was afraid I would crash or flip the ambulance."
The alleged toxic attack happened during a week that even by Syria's standards was especially punishing. It was described by the UN High Commissioner for Human Rights in a statement as "one of the bloodiest periods of the entire conflict with wave after wave of deadly airstrikes," and "no-holds-barred" in nature.
When it was bombed, teams had to evacuate staff and patients as well as premature babies, who were removed from their incubators, wrapped in blankets and sent away in ambulances in the hopes they would arrive at another medical facility before they died.
Laith al-Abdullah, 40, currently with the White Helmets but an accountant by trade, said it was the toughest period yet.
"I mean these last days, it has been a tragedy. It's so hard to do our work when you have aircraft overhead, when you know the next strike is coming," he said. "We have learned that we have seven minutes give or take within strikes. You just have to save whomever you can."
Mahmoud Kafratoune's father was among those affected by the chemical attack, only to be killed days later in the same area by another strike as he was stacking sacks of grain in a truck.
"We had left the neighborhood, but my father stayed because of the house and his work," the 20-year-old recalled. "My mother began beating her head and sobbing hysterically. We had just seen my father, he said he would come see us in two days, but then he never returned."
Aref Alkrez contributed to this report.