An explosion rocked a Cosmo Oil Co. refinery in Ichihara, Chiba Prefecture, on Sunday morning, causing a fire that took three hours to control.
No injuries were reported.
There were 57 workers at the refinery on the shores of the Goi industrial district in Ichihara when the blast occurred at around 5:30 a.m., the Ichihara Fire Department said.
Thick columns of black smoke billowed from the refinery shortly after the explosion. Fire officials said the blaze was brought under control at around 8:40 a.m.
According to police and the fire department, the explosion occurred at a facility where sulfur is removed from heavy oil. The facility is located at the center of the 120,000-sq.-meter refinery.
The blast damaged pipes and caused hydrogen gas to leak, they said.
Cosmo Oil officials said six workers on the night shift were in an instrument control room about 20 meters from the blast site.
They reported seeing nothing abnormal when they checked their instruments at around 4 a.m., the officials said.
"We are sorry for causing this trouble. We will investigate the cause of the incident," said Takashi Yashima, the head of the refinery.
The refinery is on a man-made island in Tokyo Bay, with other chemical plants and power generation facilities located nearby.
