A fire that burned for days at a Minnesota recycling facility last month was accidental and may have been sparked by a discarded battery, fire investigators said Wednesday.

An investigator for the state fire marshal's division found no evidence the fire that broke out Feb. 18 at Northern Metal Recycling in Becker was intentional. Law officers also found no indication in the fresh snow that anyone had tried to climb the metal pile that stood 60 feet (18 meters) tall. The fire started 20 to 30 feet (6 to 9 meters) into a pile of crushed cars, appliances and scrap metal.
Workers told investigators that while batteries are supposed to be removed from vehicles before they're received at the yard, some occasionally slip through, the Star Tribune reported.
Over 100 fire departments responded to the blaze, which sent up a thick plume of black smoke. Residents of the city about 50 miles (80 kilometers) northwest of Minneapolis were not asked to evacuate.
Northern Metal moved its shredding operation from Minneapolis to Becker last year after the Minnesota Pollution Control Agency ordered it shut down because of high levels of air pollution and inaccurately recorded pollution.