South Korean authorities on Thursday were investigating what caused a fire that killed 38 construction workers in one of the country’s deadliest fires in years.

The explosion that swept through a warehouse being built in Icheon, just south of Seoul, also injured 10 others Wednesday.

At the time of the fire, 78 workers had been inside the warehouse and all have been accounted for, local fire official Park Su-jong said.

Park said 29 had been identified and DNA tests were being conducted for the rest. Of those identified so far, all were male and include two Pakistanis and one Chinese. The others were South Korean.

A team of fire, police and other officials entered the warehouse on Thursday morning to examine exactly what triggered the blaze. Authorities presume an ignition of oil mist caused an explosion too suddenly for workers to escape, Icheon Fire Chief Seo Seung-hyun said Wednesday.

Police separately were investigating if the construction has involved any violation of local building laws. Police questioned six construction and other company officials involved in the warehouse construction and banned 15 company officials from leaving South Korea, a police officer said, requesting anonymity because an investigation was underway.

South Korea has struggled for decades to improve safety standards and change widespread attitudes that treat safety as subservient to economic progress and convenience.

Forty-six people died in 2018 when a fire ripped through a small hospital with no sprinkler systems in the southern city of Miryang. A fire at a refrigerated warehouse in Icheon in 2008 killed 40 workers.