In a historical twist, many people like them, descendants of Koreans who migrated to northeastern China in the early 20th century to escape Japan’s brutal colonial rule, have come to South Korea in recent decades in search of better-paying jobs in their ancestral homeland, now one of the world’s wealthiest countries.

For more than a dozen of them, the Korean dream ended in horror on Monday when a fire unleashed toxic gas to engulf a lithium-ion battery factory where they worked. Of the 23 workers killed at the Hwaseong plant south of Seoul, 12 women and five men were from China, ranging in age from 23 to 48, according to officials. Most were ethnic Koreans.

The disaster has once again drawn attention to the harsh realities facing migrant workers from China and elsewhere.Population continues to declinethe number of foreign workers in South KoreaRapid increaseThese people are at the bottom of the labor market and do the so-called “3D” jobs that Koreans are unwilling to do, namely dirty, difficult and dangerous jobs.

The work is particularly deadly in South Korea, which is the most developed countryOne of the countries with the highest workplace death ratesA recent study shows that foreign workers are almost as likely to die in workplace accidents as the average Korean worker.three times.

“These North Koreans from China are the product of South Korea’s painful history,” said Samuel Oh, director of the Asan Migrant Workers Center near Seoul. “They came to South Korea hoping for a better life for themselves and their children. But they often end up facing discrimination and not getting proper safety protection.”

The fire in Hwaseong gives us a glimpse into the problem.

South Korea is a major producer of lithium batteries, which power smartphones, electric cars and many other products. But South Korean regulations still view lithium primarily as an environmental issue rather than a potential fire hazard, leaving gaps in safety standards for companies involved, said Lee Yong-jae, a professor of fire science at Kyung Min University north of Seoul.

The Hwaseong plant is run by a small company called Aricell, which supplies batteries to South Korea’s military and other customers. In general, smaller companies in the chemical and battery industries tend to have worse safety records than larger companies, industry experts say.

“Fatalities from these types of fires are rare,” said Emma Sutcliffe, director of the EV FireSafe program in Melbourne, Australia, which tracks battery fires.

Sutcliffe and other experts said battery production facilities are typically confined to one floor to allow for easy evacuation in an emergency and are separate from other offices or buildings. In Aricell’s Building 3, workers were packaging batteries for delivery on the second floor, and the fire broke out directly above the battery production workshop.

Like other small manufacturers in South Korea, Aricell relies heavily on foreign labor to keep costs down. Experts say these workers are on short-term temporary contracts, rarely receive adequate safety training or work at a factory long enough to become familiar with the factory’s architectural structure, such as the location of emergency exits.

Lee said the walls of Building 3 were made of thin metal sheets with plastic insulation in between, which could easily catch fire. The fire department said the factory also stored flammable materials near a door at the second-floor exit, another security lapse.

Once a lithium battery catches fire, it becomes extremely hot inside and is difficult to extinguish. According to images taken by internal security cameras cited by the fire department in the report, the Aricell fire began when white smoke began to come out of a battery near the exit. Within 37 seconds, a series of batteries began to explode, emitting white-orange flames. Seconds later, thick toxic smoke filled the floor.

Almost all the dead were found clustered against the wall opposite the exit. There was no exit from that wall.

The bodies, which were badly burned, were assigned numbers before DNA testing and family members from China helped to identify them.

“The bodies were burnt and the clothes melted,” said Li Jianhao, an ambulance driver, after taking one of the victims to a funeral home. “They were burned beyond recognition.”

On Tuesday, Aricell’s head, Park Soon-gwan, apologized for the deaths. But he denied the factory lacked safety measures and said workers were trained in emergency situations. Police said they planned to question Park and other company executives on possible criminal charges of violating industrial safety laws.

Human rights groups have long protested working conditions on South Korea’s many small farms and factories, most of which could not function without workers from poorer countries such as Vietnam, Cambodia, Nepal, the Philippines and Bangladesh. But for many in those countries, as well as an estimated 2 million ethnic Koreans in China, the opportunity to earn money far outweighs the dangers.

“The income here in three days is equivalent to a month’s work in my hometown,” said Li Fugui, a 33-year-old Korean carpenter from Heilongjiang Province in northeast China.

He said he planned to work in South Korea for another two years. “I want to save some money to go back home,” he said. “It will be enough for the rest of my life.”

Korean Chinese understand the South Korean language and culture, are called “fellow countrymen,” and many South Korean managers prefer to hire them. But not everyone welcomes them. Unions complain they take jobs from South Koreans and drive down wages, and many view them as low-skilled workers who speak Korean with a distinct accent.

“They are treated as second- and third-class citizens in South Korea,” said Park Chun-woong, a Christian pastor who has campaigned for the rights of migrant workers, including ethnic Koreans from China.

Kim Sung-dae, a Methodist minister who also lobbies for migrant workers, blames the South Korean government for some of the group’s dangerous working conditions.

Two years ago, the country enacted a law that could send executives to jail if companies that employ temporary workers cause fatal accidents involving negligence, but until this year the law did not apply to factories with fewer than 50 workers.

Xu Guoli, 58, an ethnic Korean who came to Hwaseong from China in 2008 and has run a supermarket there for five years, said the recent economic weakness has prompted many Chinese to want to work in factories like Aricell.

But she was still surprised that there were more foreign workers than Koreans at the battery factory.

“Everyone wants to know why all the foreigners are here,” she said. “Why aren’t Koreans working there?”

Government policies leave migrant workers, who often need their employer’s permission to change jobs, with little say in choosing or changing employers, which advocates say leaves them vulnerable to greedy bosses, discrimination and abuse.

“Under such a system, they can hardly complain about unsafe working conditions,” Jinda said. “This system encourages accidents in the workplace.”