Mishawaka Battalion Chief Mike Croy said the all-clear was given about 7 a.m. Saturday after air monitoring showed it was safe for residents to return home within a one-mile radius of the old Baycote factory.
The fire inside a small area of the factory in Mishawaka released a chemical vapor cloud of unknown substances over the city's south side, prompting officials to order the precautionary evacuation, Croy said.
"They really weren't sure what the chemical was and what effects it might have on people," he said.
Mishawaka is about 10 miles east of South Bend.
Jack Walker, who lives about a block from the idle plant, said he didn't hesitate to load his two dogs into his car late Friday night when officials issued an evacuation order after the fire produced a strange-smelling cloud.
"I was out in my front yard and it smelled funny - it was a smell like I'd never smelled before," he said Saturday afternoon, hours after he returned home. "It was a really weird smell."
Walker, who suffers from asthma, said the aroma wafting from the plant didn't irritate his lungs or his eyes but worried him nonetheless. He drove outside the evacuation area to his mother's home, where he spent the night.
Croy said it isn't clear how many people were actually evacuated, but he believes about 200 people live within the one-mile evacuation zone around the factory, an area that is a mix of industries and homes.
The Baycote complex was once an electroplating and metal finishing business, but it's been vacant since 2008. The site is in the midst of a cleanup by the U.S. Environmental Protection Agency that began this spring.
EPA on-scene coordinator Paul Atkociunas said more than 50,000 gallons of liquid and solid chemicals were stored there when the cleanup started but that the bulk of the material has already been removed.
He said a cleanup crew working for the EPA put some solid "sludge-like" chemicals into a plastic-lined cardboard box Friday, and those chemicals self-combusted and caught fire about 7:15 p.m. - hours after the workers had left the building.
Atkociunas said the white cloud produced by the fire may have contained hydrogen cyanide, hydrogen sulfide and sulfur dioxide based on the chemicals that burned. He said the fire was confined to the storage container that caught fire.
He called it an "unfortunate accident" but praised local fire officials for acting quickly and alerting him and other EPA officials once the blaze was spotted.
Atkociunas said the EPA will analyze what caused the fire and reassess its approach to removing the remaining chemicals from the site.
"We're going to be taking a look back at our procedures to make sure this doesn't happen again," he said.
(Copyright 2012 by The Associated Press. All Rights Reserved.)