According to Nippon Steel & Sumitomo Metal, the 5 January fire started inside an inverter panel in the thyristor room serving auxiliary rolling equipment. The company said it believes arcing caused by a malfunctioning component in the panel ignited the fire, which spread to adjacent panels.  

The fire burned up almost all of the control panels and cables in the electrical room and caused structural damage to the electrical room itself. As a result, the rolling line was left inoperable. 

The company said it has taken a variety of steps to prevent such a fire from occurring again. 

"We sincerely regret the great trouble, anxiety, and inconvenience caused to the people of the local community, our business partners and those concerned by this accident," the company said in a statement.