PORTLAND, ORE. – The tear gas started early Friday night, interrupting a line of drums and dancing, chanting protesters, an artist painting in oils underneath a tree in the park and a man with a microphone speaking about the issues of racial justice and policing at the center of these nightly demonstrations.

“Hey guys, don’t panic, don’t panic,” the man said from the steps of the Multnomah County Justice Center, one block over from the federal courthouse in downtown Portland. “All you first-timers out here, it’s just tear gas. Everybody just relax.”

As if on cue, a brigade of orange-shirted men with leaf blowers descended on the cloud, revved their engines and blew the tear gas away. The crowd cheered.

“Thank you leaf-blower dads!” shouted a young woman.

Every night for more than a week, federal agents have been unleashing a barrage of tear gas on crowds of demonstrators, a small number of whom have lobbed fireworks at the federal courthouse, set fires and tried to tear down a tall, reinforced metal fence surrounding the building. The noxious fog burns and stings. Some people who get hit with the dense plumes of chemicals that cloud Portland’s streets each night feel like they can’t breathe, like their eyes are on fire, like they might vomit onto the asphalt.

Though some Portlanders have been able to get respirators, goggles and gas masks to protect themselves from the worst effects of the riot control agent known as CS gas, many others have turned to a familiar landscaping tool to blow the chemicals away: leaf blowers.

The loud, pressurized air machines typically used to clear grass, leaves and other lawn debris are surprisingly effective tools at clearing caustic chemicals from the air. They’re so effective that on Friday night, federal agents frustrated at being caught in up in a redirected cloud of tear gas, showed up to the demonstration with their own handheld blowers.

The leaf-blower wars were on.

“I’m totally impressed with all the courage we’re seeing from just normal people who have taken it on themselves to come out here and stand up for our right to protest,” said Eddie, a 35-year-old Portlander who declined to give his last name out of fear of retaliation from federal officers.

Eddie, who wore a gas mask and leather jacket for protection from projectiles, said that although he’s not a dad, he was inspired by the formation of the “Leaf blower dads group” to bring a blower to the demonstrations. He even fashioned a leather strap out of a belt so he could sling it over his shoulder and carry it around all night.

“You’ve got the moms out here on the front line and the dads backing them up with the leaf blowers,” he said. “It’s pretty amazing.”

CS gas, or 2-chlorobenzalmalononitrile, has been classified as a chemical weapon. Its use is banned on the battlefield by nearly every country in the world, including the United States. But it is legal to use domestically by police and federal agents to disperse crowds.

Typically, police fire the agent once or twice to clear crowds and encourage people to move away from an area, said Michelle Heisler, the medical director of Physicians for Human Rights. But in Portland, federal agents have been unleashing the chemicals repeatedly for hours. This sustained cascade makes it difficult for peaceful demonstrators to avoid being hit and runs the risk of ensnaring bystanders in the area, she said.

“The people here are not dispersing, so these federal officials are just launching massive amounts of it,” Heisler said. “It can blind people. It can kill people through chemical burns — especially people who have asthma or other lung diseases. This is dangerous stuff.”

Enter the leaf blowers.

A group of self-identified Portland dads, inspired by the “Wall of Moms” that forms a protective human shield at the front of nightly protests near the Mark O. Hatfield Courthouse, set out to help clear the air at protests by arming themselves with leaf blowers. They are known collectively as “DadBloc” and “Leaf-Blower Dads” and turn up to the protests wearing orange shirts to compliment the moms’ yellow ones.

Each night, their numbers have swelled.

On Friday, they were joined by other burgeoning groups — the veteran-led Wall of Vets, green-shirted Teachers Against Tyrants, the pizza-box carrying ChefBloc, health-care workers in scrubs and Lawyers for Black Lives, who turned up at the protest in suits and ties.

Tessa Terry, 30, and her husband, Leshan Terry, 31, are Navy veterans who helped organize the Portland “Wall of Vets” after seeing a video of federal agents beating a Navy veteran with batons so badly they broke his hand. On Friday night, they attended their first demonstration since President Donald Trump sent dozens of federal law enforcement officers to Portland — a move that Portland Mayor Ted Wheeler, who was tear-gassed with the crowd earlier this week, and Oregon Gov. Kate Brown have likened to a hostile occupation. Both Wheeler and Brown are Democrats.

Though the Terrys had been through military training that puts recruits in a gas chamber, where they have to take off their masks and breathe in the fumes, Tessa Terry said, the chemicals in the air on Friday were overwhelming.

“They’re not just doing one or two — or even three or four — in a night,” Tessa Terry said. “They’re popping them off the entire night, and I’ve never seen anything like that.”

Canisters found strewn about downtown streets indicate some of the gas may be expired, which experts said could make the chemicals feel more potent.

Human rights groups and health professionals have cautioned that tear gas could help spread the still-raging coronavirus because it irritates the lungs, makes people cough and causes a sensation that many react to by ripping off cloth masks they may be wearing to help mitigate the spread of the disease.

On their second night, the Terrys will be more prepared, they said. Lashan Terry, a former aviation mechanic, will be bringing his own blower.

Part of the reason the blowers are so effective against tear gas, experts said, is because despite the name, the chemicals in the canisters are actually an aerosol rather than a typical gas. That means tiny powder-like particles are dispersed into the air, where they hang and drift like a menacing fog.

Should a person be hit by the chemical substance, the particles stick to their body, clothes and any other surface they come into contact with, said Lewis Nelson, a Rutgers New Jersey Medical School professor who also works at the New Jersey Poison Center.

When the leaf blowers turn their blast of air on the chemical cloud, Nelson said, it sends the cloud in another direction. If the protesters push the tear gas back toward federal agents, the particles could latch onto their uniforms, helmets and other gear.

It makes sense then, Heisler said, that the agents would muster their own arsenal of blowers.

It was not clear where all these leaf blowers were coming from. They range in size and firepower. One man on a recent night held a tiny handheld blower above his head as a cloud of gas crept closer. The blower was about one foot from end to end. On Friday, several men carried large blowers powered by fuel packs strapped to their backs.

Hardware stores in the Portland area said they hadn’t noticed a rush on leaf-blowers in recent weeks, but several managers noted that summer is typically a hot season for leaf-blower sales.

Just after midnight Saturday, a gas canister landed on the south side of the federal courthouse, just past a large banner that protesters had hung on the reinforced black fence around the courthouse with the letters BLM, an abbreviation for Black Lives Matter.

“Throw it back!” yelled the crowd. “Get rid of it!”

A man with a leaf blower strapped to his back snuffed out a lit cigarette and sighed.

“Well,” he said to himself. “Time to get gassed again.”

He revved up the machine, adjusted its straps and marched forward into the gathering fog.