Five workers suffocated to death on Friday at a steel plant in the port city of Dangjin after gas leaked from a furnace, authorities said.

The workers, employed by a subcontractor of Hyundai Steel Co., were found dead at around 1:40 a.m. inside the 8-meter-deep rotating furnace in the city, some 123 kilometers south of Seoul, after argon gas leaked from the furnace, according to the authorities.

The victims were removing the scaffolding that had been used for regularly scheduled repair work from inside the furnace when argon gas leaked from a value causing a lack of oxygen within the container, according to the country‘s second-largest steelmaker.

Though argon is nontoxic, it is denser than air so that it is considered dangerous in closed areas, according to experts. The gas is also hard to detect as it is colorless and odorless.

“Argon gas is used to check the piping system of the furnace.

After the test, they should have made sure all gas was removed,” said a Hyundai Steel official.

“The workers appear not to have equipped themselves with the required safety equipment to prepare for possible gas leakage,” he added.

Police said they, along with the local labor administration and Korea Gas Safety Corp., are working on finding the exact cause of the incident.

“Though the workers did not abide by safety regulations, Hyundai also should shoulder responsibility for its failure to properly supervise them as such a job inside the furnace deems highly risky,” said an official of the Ministry of Employment and Labor, vowing “a stern punishment in case of illegality.”

Offering condolences to bereaved families, Hyundai Steel apologized for “causing concern among the people.”

“We are proactively cooperating with government investigation.

We will spare no effort to conduct a safety check to prevent the recurrence of such accidents,” the steel maker said in a statement. (Yonhap News)