South Korea’s Deadliest Gas Explosion Began with a Drilling Error

A powerful gas explosion struck the South Korean city of Daegu in 1995, killing 100 people.

According to Yonhap, the disaster occurred at 7.52am on 28 April 1995 at the construction site for Section 2 of Daegu Subway Line 1, directly in front of Yeongnam Middle School in Sangin-dong, Dalseo-gu, Daegu.

The blast was triggered by city gas leaking from a nearby building construction site. The gas flowed into and accumulated in the underground section of the subway construction site.

The incident killed 100 people and left 143 with serious or minor injuries.

The damage was extensive. A total of 91 vehicles, including city buses, were destroyed, as were 74 nearby buildings and homes.

The day before the explosion, construction subcontractor Pyojun Development Co. began grouting on an eight-metre-wide access road south of the Daebaek Plaza Sangin branch project site. It drilled 22 holes.

Drilling resumed using two machines. One drill rod pierced a buried 100-millimetre-diameter medium-pressure city gas pipe at a depth of 1.7 metres, creating a hole 80 millimetres wide.

High-pressure city gas, at 4.2 kg/cm², escaped rapidly, seeped through the ground and entered a 400-millimetre-diameter stormwater drain 1.4 metres from the leak. It then travelled 77 metres through the drainage system and reached the underground area of the subway construction site.

About 40 minutes after the leak began, the accumulated gas ignited from a source that has not been identified. The resulting blast occurred while around 60 workers were at the site.

Investigators concluded that the explosion was caused by the drilling error. The drilling had also been carried out without an official road excavation permit from the authorities.