The No. 2 bar mill at Aichi Steel’s Chita plant had been offline since 8 January, when a reheat furnace that was being fired up exploded. No one was injured in the blast, the company has said.

The plant supplies specialty steel for Toyota engine, transmission and chassis components. The outage created a parts shortage, which forced Toyota to halt its production lines in Japan for about a week in February.

Toyota owns approximately 33 percent of the steelmaker.  

In a statement, Aichi Steel said human error is to blame for the accident.

“During restarting after regular maintenance, the pre-ignition air purge process was not carried out. Further, (an) incorrect work procedure was followed when fuel gas was run through the lines, leading to gas flowing into the furnace. As a result, the pilot burner flame ignited the accumulated gas.”

The company said that it would review procedures with employees and install interlock devices as a fail-safe.

“We are implementing thorough measures to prevent a reoccurrence of this situation, and are working to strengthen our production and supply systems to rebuild our customers’ trust and peace of mind,” the company said.