A fire at the ConocoPhillips refinery that spewed thick black smoke into the air on Christmas Eve was caused when a heater inside the tank ignited oil vapors, a company official said Friday.
The fire destroyed a tank that held asphalt and pitch, which is feed stock for the refinery’s coker. The coker processes heavier crude oil products into lighter materials such as gasoline and diesel.
Clint Young, a refinery spokesman, said the company’s investigation found that while oil was being removed from the tank, the product level fell below a heater inside the tank.
“That caused the heater to increase in temperature and ignite vapors inside the tank,’’ Young said in an e-mail to The Gazette.
“We are implementing operational changes to prevent fires from occurring when we remove products from tanks in the future,” he said.
The company followed its plan to communicate with employees, neighbors, public officials and nearby businesses, Young said.
“We apologize to any of our near neighbors who we did not reach through these efforts,” he said. “We certainly regret that and any other inconveniences resulting from the fire.”
Also Friday, Assistant City Administrator Bruce McCandless sent an e-mail to the mayor and council members with a similar explanation of the fire after a citizen had contacted them Thursday for information.
While the Billings Fire Department responded, it did not investigate the fire and so could not disclose any additional information, McCandless said. The Fire Department responded as part of a mutual-aid agreement.
A refinery representative Friday offered to present the results of the investigation to the council at a future meeting, McCandless said.
No one was injured during the fire, which began about 3:20 p.m. and burned for 2 1/2 hours. The blaze was contained to the tank, which was left collapsed.
Fire crews from the CHS refinery in Laurel and ExxonMobil refinery in Lockwood also assisted ConocoPhillips firefighters.
Jim Hughes, an environmental specialist with the state Department of Environmental Quality, said ConocoPhillips reported emissions from the fire that included 6.8 tons of sulfur dioxide, 10.4 tons of particulate matter, 5 tons of carbon monoxide, 1.5 tons of hydrocarbons and 400 pounds of nitrogen oxides.
There will be no enforcement action because the fire is considered to be a malfunction, Hughes said.
The fire triggered an odor complaint and calls about soot fallout on the South Side. The smoke plume traveled up the Yellowstone Valley. A sulfur dioxide monitor in Laurel recorded low concentrations of the pollutant.