A toxic leak at Samsung Electronics' semiconductor plant in Hwaseong, Gyeonggi Province on Sunday killed one person and injured four others.
The chipmaker failed to report the accident for 25 hours until one worker died.
Samsung found the leak of hydrofluoric acid from one of the valves of a 500-liter storage tank around 1:31 p.m. on Sunday, the firm said. Earlier at 1:22 p.m., a gas alarm had gone off.
According to the authorities, the leak occurred on Sunday morning, followed by another leak during recharging of the gas after a defective valve was replaced at 3:45 a.m. on Monday.