As flames rip through Los Angeles County, burning restaurants, businesses, and whole blocks of houses, it’s clear that the threat of urban fire has returned to the United States. But this time, the urban landscape is different: Modern homes are full of plastic, turning house fires into chemical-laced infernos that burn hotter, faster, and more toxic than their predecessors.

Firefighters are warning that the smoke pouring out of neighborhoods in Southern California is a poisonous soup, in part because of the ubiquity of plastics and other petrochemical products inside them. “It’s one of the reasons why we can’t put firefighters in front of these houses,” the Cal Fire battalion chief David Acuna told me on Monday. After any lifesaving work has been done, keeping firefighters in the toxic air is too great a risk.

Very few fixtures of the modern home are entirely free of plastic. If your couch is like many available on the market today, it’s made of polyester fabric (plastic) wrapped around polyurethane foam (plastic). When polyurethane foam burns, it releases potentially deadly hydrogen-cyanide gas. Perhaps those plastic-wrapped plastic cushions sit on a frame of solid wood, or perhaps the frame is made from an engineered wood product held together with polymer-based glues (plastic). Consider, too, the ubiquity of vinyl plank flooring, popular for its resistance to scuffing, and vinyl siding, admired for its durability. Then there is foam insulation, laminate countertops, and the many synthetic textiles in our bedding and curtains and carpets. Nearly all house paint on the market is best understood as pigment suspended in liquid plastic.  

Research has long shown that exposure to the tiny particles that make up wildfire smoke is a major health hazard; as I’ve written before, wildfire smoke kills thousands of people prematurely each year and is linked to a range of maladies. Burning trees release gases such as carbon monoxide and carbon dioxide, along with tiny solid particles called PM2.5, which can penetrate deep into a person’s lungs and circulate in their blood stream, and are linked to heart and lung problems, low birth weight, preterm birth, and cognitive impairment. A burning town takes many of the chemical hazards of a burning forest and adds in a suite of new ones, Nadine Borduas-Dedekind, an atmospheric chemist at the University of British Columbia, told me. As structure fires eat through the plethora of materials inside a home, they can release not just hydrogen-cyanide gas but also hydrochloric acid, dioxins, furans, aerosolized phthalates, and a range of other gaseous contaminants broadly known as volatile organic compounds. Some may be harmless. Others are associated with health problems. As gas-detection technology improves, “we’re discovering new molecules of incomplete combustion that we didn’t know existed,” Borduas-Dedekind said. “When you’re burning a home or an entire neighborhood, we don’t have a handle on the breadth of VOCs being emitted.” And many of these can react with one another in the atmosphere, creating yet more compounds. Whereas N95 masks are good for filtering out the fine particles associated with fire smoke, they do nothing for these gases; only a gas mask can filter them out.

[Read: You have every reason to avoid breathing wildfire smoke]

Plastic is made from petroleum, and petroleum burns fast and hot. A retired Maryland state fire marshal told Newsweek that, from a fire perspective, a typical couch is akin to a block of gasoline. Acuna invited me to think of placing a log on a campfire: It takes some time to heat up, charring first. It eventually ignites and becomes a steady fire, releasing its heat at a slow, consistent rate over, say, 20 minutes. If you threw a two-liter soda bottle on a campfire (which is a highly inadvisable thing to do), it would begin to distort immediately. Within several seconds it would ignite and burn fast.

In 2020, the Fire Safety Research Institute set two living rooms on fire, on purpose. Both were identical in size and full of furnishings in an identical arrangement. But in one room, almost everything was synthetic: a polyurethane-foam sofa covered in polyester fabric sat behind an engineered-wood coffee table, both set on a polyolefin carpet. The curtains were polyester, and a polyester throw blanket was draped on the couch. In the other room, a wood sofa with cotton cushions sat on a hardwood floor, along with a solid-wood coffee table. The curtains and throw blanket were cotton. In the natural-material room, the cotton couch appeared to light easily, and then maintained a steady flame where it was lit, releasing little smoke. After 26 minutes, the flames had spread to the other side of the couch, but the rest of the room was still intact, if smoky. Meanwhile, in the synthetic room, a thick dark smoke rose out of the flame on the polyester couch. At just under five minutes, a flash of orange flame consumed the whole room all at once. “Flashover,” firefighters call it—when escape becomes impossible. In the natural-material room, flashover took longer than 30 minutes. Perhaps that difference helps explain why, although the rate of home fires in the U.S. has more than halved since 1980, more people are dying in their homes when they do catch fire.

[Read: How bad are plastics, really?]

When I spoke with Acuna, of Cal Fire, he was sitting in his office, fielding calls from reporters. He looked around the room. “I’m struggling right now to find anything that is of a natural material. In fact, the only thing I can find is my notebook,” he said. Plastic, he added, is undeniably useful. But it comes with a clear risk. One day, if fire strikes, “it will burn faster, and it will burn hotter.” The advantages will turn to threats.

In an ember storm, every opening in a house is a portal to hell. A vent without a screen, a crack in the siding, a missing roof tile—each is an opportunity for a spark to smolder. A gutter full of dry leaves is a cradle for an inferno. Think of a rosebush against a bedroom window: fire food. The roses burn first, melting the vinyl seal around the window. The glass pane falls. A shoal of embers enter the house like a school of glowing fish. Then the house is lost.

As the Palisades Fire, just 8 percent contained this morning, and the Eaton Fire, still uncontained, devour Los Angeles neighborhoods, one thing is clear: Urban fire in the U.S. is coming back. For generations, American cities would burn in era-defining conflagrations: the Great Chicago Fire in 1871, the San Francisco fires of 1906. Then came fire-prevention building codes, which made large city burns a memory of a more naive time. Generations of western firefighters turned, instead, toward wildland burns, the big forest devastations. An urban conflagration was the worst-case scenario, the one they hoped they’d never see. And for a long time, they mostly didn’t.

Now more people live at the flammable edges of wildlands, making places that are primed to burn into de facto suburbs. That, combined with the water whiplash that climate change has visited on parts of California—extraordinarily wet years followed by extraordinarily dry ones—means the region is at risk for urban fire once again. And our ability to fight the most extreme fire conditions has reached its limit. The Palisades Fire alone has already destroyed more than 5,300 structures and the Eaton Fire more than 4,000, making both among the most destructive fires in California’s history. When the worst factors align, the fires are beyond what firefighting can meaningfully battle. With climate change, this type of fire will only grow more frequent.

The start of the Palisades and Eaton Fires was a case of terrible timing: A drought had turned abundant vegetation into crisp fire fuel, and the winter rains were absent. A strong bout of Santa Ana winds made what was already probable fire weather into all but a guarantee. Something—it remains to be seen what—ignited these blazes, and once they started, there was nothing anyone could do to stop them. The winds, speeding up to 100 miles an hour at times, sent showers of embers far across the landscape to ignite spot fires. The high winds meant that traditional firefighting was, at least in the beginning, all but impossible, David Acuna, a battalion chief for Cal Fire, told me: He saw videos of firefighters pointing their hoses toward flames, and the wind blowing the water in the other direction. And for a while, fire planes couldn’t fly. Even if they had, it wouldn’t have mattered, Acuna said. The fire retardant or water they would have dropped would have blown away, like the hose water. “It’s just physics,” he said.

California, and Southern California in particular, has some of the most well-equipped firefighting forces in the world, which have had to think more about fire than perhaps any other in the United States. On his YouTube livestream discussing the fires, the climate scientist Daniel Swain compared the combined fleet of vehicles, aircraft, and personnel to the army of a small nation. If these firefighters couldn’t quickly get this fire contained, likely no one could. This week’s series of fires is testing the upper limits of the profession’s capacity to fight wind-driven fires under dry conditions, Swain said, and rather than call these firefighters incompetent, it’s better to wonder how “all of this has unfolded despite that.”  

The reality is that in conditions like these, once a few houses caught fire in the Pacific Palisades, even the best firefighting could likely do little to keep the blaze from spreading, Michael Wara, a former member of California’s wildfire commission who now directs a climate-and-energy-policy program at Stanford, told me. “Firefighting is not going to be effective in the context we saw a few days ago,” when winds were highest, he said. “You could put a fire truck in every driveway and it would not matter.” He recounted that he was once offered a job at UCLA, but when the university took him to look at potential places to live in the Pacific Palisades, he immediately saw hazards. “It had terrible evacuation routes, but also the street layout was aligned with the Santa Ana winds so that the houses would burn down like dominoes,” he said. “The houses themselves were built very, very close together, so that the radiant heat from one house would ignite the house next door.”

In California, the shift toward ungovernable fires in populated places has been under way for several years. For the former Cal Fire chief deputy director Christopher Anthony, who retired in 2023, the turning point was 2017, when wildfires in populated places in Northern California’s wine country killed 44 people and burned nearly a quarter million acres. The firefighting profession, he told me, started to recognize then that fortifying communities before these more ferocious blazes start would be the only meaningful way to change their outcome. The Camp Fire, which decimated the town of Paradise in 2018, “was the moment that we realized that this wasn’t, you know, an anomaly,” he said. The new fire regime was here. This new kind of fire, once begun, would “very quickly overwhelm the operational capabilities of all of the fire agencies to be able to effectively respond,” he said.

As Wara put it, in fires like these, houses survive, or don’t, on their own. Sealed against ember incursion with screened vents, built using fire-resistant materials, separated from anything flammable—fencing, firewood, but especially vegetation—by at least five feet, a house has a chance. In 2020, California passed a law (yet to be enforced) requiring such borders around houses where fire hazard is highest. It’s a hard sell, having five feet of stone and concrete lining the perimeter of one’s house, instead of California’s many floral delights. Making that the norm would require a serious social shift. But it could meaningfully cut losses, Kate Dargan, a former California state fire marshal, told me.

Still, eliminating the risk of this type of wind-driven fire is now impossible. Dargan started out in wildland firefighting in the 1970s, but now she and other firefighters see the work they did, of putting out all possible blazes, as “somewhat misguided.” Fire is a natural and necessary part of California’s ecosystem, and suppressing it entirely only stokes bigger blazes later. She wants to see the state further embrace preventative fires, to restore it to its natural cycles. But the fires in Southern California this week are a different story, unlikely to have been prevented by prescribed burns alone. When the humidity drops low and the land is in the middle of a drought and the winds are blowing at 100 miles an hour, “we’re not going to prevent losses completely,” Dargan said. “And with climate change, those conditions are likely to occur more frequently.” Avoiding all loss would mean leaving L.A. altogether.

Rebuilding means choosing a different kind of future. Dargan hopes that the Pacific Palisades rebuilds with fire safety in mind; if it does, it will have a better chance of not going through this kind of experience again. Some may still want to grow a rosebush outside their window. After this is over, the bargaining with nature will begin. “Every community gets to pick how safe they want to be,” Dargan said.