Fire investigators say they are still trying to establish how a blaze broke out at Tata Steel's Port Talbot plant.
Mid and West Wales Fire and Rescue crews were called to the site at about 08:00 GMT on Thursday when the fire started in the coke area of the site.
Plant officials initially suggested a lightning strike may have been responsible for the fire.
But the fire service said their investigations are continuing - focusing on a gas supply line.
"Our crews did respond and react exceptionally well to the incident, which commenced following a power failure on site," said the fire service's head of resources, Iwan Cray.
"The imagery of the scene was spectacular and thus triggered reactions from individuals who were miles away but our crews were very quick to instigate their reactive skills, applying knowledge and understanding of the risks faced to ensure a very rapid containment of the incident."
The blaze was extinguished within an hour, and crews remained on site to monitor the situation until the early evening, with production resumed by the end of the day.
"The works continues to operate as-normal, and those affected areas have been brought back into operation as soon as possible," said Tata Steel's Robert Dangerfield.
"Investigations are still under way, working with relevant business partners, into the cause of the incident."