At about 11:31 a.m. on the 25th, four people working inside a septic tank installed in the basement of a zinc processing company in the Duryu Industrial Area in Angang-eup, Gyeongju, North Gyeongsang Province, collapsed from asphyxiation.
According to fire authorities and police, two workers in their 40s to 50s who were taken to a hospital died. The other two were also believed to be in critical condition.
Another worker outside is said to have found them collapsed at a depth of about 2 meters inside the septic tank and reported it to authorities.
Police said they were employees of an outside company based in Gyeonggi Province that replaces and services cylinders.
Police said they worked once on painting inside the septic tank on the 17th and collapsed while doing piping work that day. Fire authorities are using a hazardous gas detector at the scene to assess conditions inside the septic tank.