“There were no injuries and air monitoring in the community showed no negative signs of fire.” Firefighters in Billings and Lockwood, Montana responded to the scene, the Billings Fire Department said. King said the cause of the fire has not been determined. “We are working diligently to better understand the incident and continue to work with the authorities,” he said. “Our main priority is the safety of our workforce and the community. We are sorry that this incident happened and we apologize for any inconvenience or inconvenience.” The refinery is located on the Yellowstone River near Lockwood, Montana, according to the ExxonMobil website. It covers 720 acres, which includes about 370 acres of underdeveloped land and urban wildlife habitat area, according to the website. CNN’s Holly Yan contributed to this report.