As much as 630,000 gallons of slurry oil - a thick fuel used in industry - spilled or burned, generating a cloud of oily soot that settled onto a nearby residential area.
There were no injuries, and the fire was out around three hours after it started.
Marathon Ashland spokesman Chuck Rice said the company had received 46 calls from Woodbury residents who had soot on their homes, on vehicles or in their swimming pools. The company was hiring cleaning services to clean up the mess, he said.
The Minnesota Pollution Control Agency determined that the soot didn't cause any environmental damage, and Rice said none of the callers to the company complained of health problems.
The fire started about 5:50 a.m. when a bolt of lightning hit a 48-foot heated tank holding about 2.5 million gallons of slurry oil.
A refinery employee witnessed the lightning strike, which apparently ignited some vapors in the tank and caused an explosion that blew the lid off.
``He said it was a pretty scary moment,'' Rice said.
The flames got hot enough to weaken the tank, causing it to rupture and spill about a fourth of its contents. The flow was contained by an earthen and clay-lined dike around the tank. There were no evacuations, and no spills of petroleum products into sewers or waterways.
Information from: St. Paul Pioneer Press
