Up to 10 liters of hydrofluoric acid, an acute poison that can damage lungs and bones and even affect the nervous system, leaked from one of the pipes at the Samsung plant in Hwaseong, 60 kilometers south of Seoul, on Sunday, officers said.
The leak occurred around 1:30 p.m. and five workers from Samsung's subcontractor, named STI Service, were called in to begin repair work at 11:00 p.m., police said, quoting Samsung officials. The repair work was finished at 4:46 a.m. Monday, but all five of the STI workers complained of pain in the neck and chest, they said.
One worker, identified only by his surname Park, collapsed at the scene and later died at a hospital in Seoul from apparent prolonged exposure, police said.
The other four, who were discharged shortly after due to minor conditions, have been readmitted to a Seoul hospital for a complete medical examination, they said.
Police called in officials from Samsung and STI late Monday to be questioned over not reporting the incident sooner, officers said.
"We were too busy handling the scene that we could not think of reporting to the authorities," the officials were quoted by the police as saying.
Police said they will investigate to determine whether the workers had access to proper safety equipment and to figure out why the tank leaked the poisonous gas in the first place.
The team will closely look into a central chemical supply system at the plant that manages the chemical substance and whether the pipes were worn-out, they said.
Samsung Electronics, meanwhile, released a statement Tuesday expressing regret and offering condolences to the victim and his family.
"The firm promises to actively cooperate with the authorities regarding the incident to thoroughly investigate the cause so we can prepare measures to prevent it from happening again," Jun Dong-soo, president of Samsung Electronics' memory division, said in the statement.
Sunday's incident marks the third gas leak in the past six months that has terrorized the country.
In September last year, some eight tons of hydrofluoric acid leaked from chemical maker Hube Globe in Gumi, about 260 kilometers southeast of Seoul, resulting in the deaths of five workers and injuries to 18 others.
The leaked gas caused massive damage, sickening more than 3,000 additional people and withering hundreds of hectares of farmlands and orchards, according to the authorities. To offer extra financial aid, the government designated the city as a special disaster zone.
Earlier this month, more than 700 residents were evacuated to safety after hydrochloric acid leaked from a 200-ton tank of the Woongjin Polysilicon plant located in Sanju, 270 kilometers southeast of Seoul.