DETROIT -

A preliminary investigation says a spontaneous reaction is to blame for a fire earlier this year in a tank at the Marathon Petroleum refinery in Detroit.

On April 27, a fire in a tank at the refinery forced the temporary evacuation of a number of area residents.

Listen: 911 calls from Marathon Refinery fire

No one was injured in the fire, which burned a tank that the company said held wastewater produced in refining processes.

Company spokesman Sid Barth told Local 4, "The ignition source was attributable to a spontaneous reaction of iron sulfide deposits with oxygen in the roof area of the tank."

Marathon Refinery tank fire Detroit

Barth said an investigation continues, but that the company has modified their process for managing oxygen content in tanks.