Police said they plan to impose the fine on Samsung and its subcontractor, named STI Service, for violating the Toxic Chemicals Control Act that stipulates the firms to notify the authorities promptly when such an incident breaks out.
Up to 10 liters of diluted hydrofluoric acid, an acute poison that can damage the lungs and bones and even affect the nervous system, leaked from one of the pipes at the main semiconductor plant of the world's largest memory chip maker in Hwaseong, 60 kilometers south of Seoul, on Sunday, officers said.
The leak occurred around 1:20 p.m., and five maintenance crew members from STI Service were called in to begin repair work at 11:00 p.m., police said, quoting Samsung officials.
The two firms, however, failed to report the incident to local authorities until one member of the crew members, identified only by his surname Park, died at a hospital in Seoul from apparent prolonged exposure, they said.
Four other workers who were discharged shortly after due to minor conditions have been readmitted for a complete medical examination, they added.
Police immediately set up an on-site joint investigation team with company officials to determine the cause of the leak.
"We will thoroughly investigate to clarify who is responsible for the incident as someone died due to poor administration," an official of the investigation team said.
Samsung has since been under intense fire for not only failing to report to the authorities promptly but also for the alleged cover-up of the incident.
"We are investigating in four different ways to determine the exact amount of leaked gas, the secondary damage, how the incident was handled by the firms afterward, and the relevant law," the official said, adding that it will take up to two weeks to figure out.
The probe will particularly be focused on whether the workers had proper safety equipment and if the pipe where the leak supposedly originated was in need of repair, officials said.
The first set of footage extracted from the closed-circuit television showed Park entering the gas room without protective clothing except for a mask, according to the police's initial report.
The family of the deceased, however, raised doubts over the police findings that Park had not worn his protective clothing.
An autopsy on Park was carried out on Wednesday, police said, and the results will come out in the next week or two.
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.