SEOUL, South Korea — Seventy-eight workers, from nine different subcontractors, were busy Wednesday laying tiles and installing cargo elevators to meet a June deadline for completing a four-story cold-storage warehouse. Another crew was coating underground walls with polyurethane foam — a cheap but efficient insulator that can easily catch fire and then emit extremely toxic fumes.
The air was heavy with highly flammable vapors, from solvents that the workers were using to dissolve polyurethane.
Around 1:30 p.m., a spark of unknown origin ignited the air.
A rapid-fire chain of explosions shook the building. Within minutes, the 107,000-square-foot warehouse in Icheon, southeast of Seoul, became an inferno — and a death trap for 38 workers. Toxic, ink-black smoke billowed up so fast that survivors later said they could hardly find the stairways out.
“I first saw black smoke billowing out of the building, followed by eight or nine explosions and flames,” Kim Yong-nam, a witness, told the all-news channel YTN. “It spread so fast that in less than two minutes, the entire building was engulfed in smoke and fire.”
It was a horror for dozens of families and an embarrassment for President Moon Jae-in, who has promised to end the catastrophic fires and other man-made disasters — often linked to lax safety standards — that have plagued South Korea for decades.
What angered many South Koreans was that the apparent causes of Wednesday’s fire were so familiar: vapors from a chemical solution filling a room where workers may have been generating sparks, with the ensuing fire fed by extremely combustible insulation.
That combination has repeatedly turned South Korean construction sites and commercial buildings into tinder boxes.
Nearly half of the dead were found on the second floor, three stories from where the fire started below ground. Forensic officials said on Thursday that some of the bodies were so badly burned that DNA analysis might be needed to identify them.
“The fumes from burning polyurethane are so toxic that you can collapse after inhaling it only once,” said Seo Seung-hyeon, a fire department chief who led the rescue operation at the warehouse. “Given the way they died with all their clothes burned away, we believe that they didn’t have time to escape.”
In recent decades, hundreds of South Koreans have died in fires with similar causes. In 1998, when a fire at a youth camp killed 23 people, 19 of them kindergartners, the high death toll was blamed in part on toxic gases from burning polystyrene.
In a 1999 building fire, a spark ignited vapors from paint thinner in an underground floor that was under renovation. Fifty-six people died, many of them teenagers, in a beer hall upstairs, which had been illegally selling liquor to minors and had no fire exits.
In 2008, 40 workers died in another cold-storage warehouse under construction in Icheon, in a fire that started almost exactly the same way that Wednesday’s did. In 2014, a similar fire in a bus terminal north of Seoul killed nine workers.
“I am sorry that similar accidents are repeating themselves,” Mr. Moon said on Wednesday. “We are not learning lessons from the past accidents.”
Mr. Moon’s predecessor, Park Geun-hye, never regained the public’s trust after more than 300 people, most of them high school students, died in the sinking of the Sewol ferry in 2014. The episode was marked by corruption and incompetence, including an initial announcement from the government that everyone on board had been rescued.
Ms. Park was eventually impeached and ousted, mostly because of an unrelated graft scandal, though the lawmakers who impeached her also cited the Sewol disaster.
Campaigning to replace her in May 2017, Mr. Moon promised to end what he called the “governmental incompetence and irresponsibility” that contributed to man-made catastrophes, and to “put human lives before everything else.”
But major fires have continued since he took office.
In December 2017, 29 people were killed in a fire at a gym and public bath complex, ignited by an electric spark and fueled by cheap, flammable insulation. So many cars were parked illegally around the building that the arrival of fire engines was delayed. And sprinklers in the building did not work.
Women trapped inside made terrified calls to their husbands, reviving painful memories of the Sewol sinking, during which teenagers trapped on the ship sent text and messages to their parents saying goodbye.
Just a month after the gym fire, another one, in a hospital that lacked sprinklers, killed 41 people, most of them elderly and immobile patients who died inhaling toxic smoke.
Later that year, a fire killed nine workers at an electronic components factory. Again, toxic smoke from polyurethane insulation was blamed, along with malfunctioning sprinklers.
Many of the fires and other man-made disasters — including the collapse of a bridge and a department store in the 1990s — that have dogged South Korea since it began rapidly industrializing during the Cold War were attributed to corruption, lax regulatory enforcement and corner-cutting on safety measures by businessmen. Those problems have never been stamped out.
Years after the sinking of the Sewol, which was overloaded and had not been properly inspected, truckers were still underreporting the weight of cargo that they loaded onto ferries.
South Korea has revised its laws to limit the use of materials like polystyrene and polyurethane as insulators, requiring more buildings to use more expensive and fire-resistant products.
But the new regulations do not apply to buildings built before 2015, and the cheap, combustible alternatives are still used on many construction sites. Similar insulation was blamed in the Grenfell Tower fire in London that killed 72 people in 2017.
The police said on Thursday that they were investigating whether work crews at the Icheon warehouse had been forced to weld and use flammable materials in the same closed space at the same time, to speed up construction.
They said they were also investigating whether the crews had fire extinguishers, an on-site fire inspector and other mandatory protections for workers who use flammable materials.
