Residents of the town of Northwood were allowed to return to their homes after being evacuated for several hours Thursday when an explosion and fire engulfed an outbuilding at the airport. The explosion happened before 8 a.m.

Sergeant Scott Bright of the Iowa State Patrol says they asked residents to evacuate as the building contained a small amount of sulphuric acid, which can cause lung damage if inhaled. “When you get chemicals involved like that and you don’t know what chemicals you’re dealing with, you take the precautionary way –we get people out of the town and away from the smoke. We don’t want anybody to get injured,” Bright says.

He says this was something new. “I’ve been on the state patrol 24 years and I can’t recall a situation like this, where we’ve had chemicals involved and we had to evacuate the whole town. But we’re thankful the evacuation process went smoothly, “Bright says.

A spokesperson at the hospital in Mason City said four people came to be treated after breathing the smoke. “That’s all we heard of — only four — so we’re thankful for that,” Bright says. He says the four people are doing fine.

The Environmental Protection Agency tested the air before allowing Northwood’s residents the all-clear to return to their homes around three-o’clock this afternoon.

Worthy County’s emergency management director called in Michael O’Neil  from neighboring Cerro Gordo county to help oversee the evacuation center six miles south in Kensett. O’Neil says the residents were very cooperative. “They were very, very good, very understanding. A lot of them were digging in and helping set up chairs. The people just reacted very, very well,” O’Neil says.

One area for the evacuees was set up at the Kensett Community Center and another was set up for the nursing home that was evacuated. Highway 65 was closed for a time while the fire was brought under control.  Bright says investigators are trying to determine the cause of the explosion and fire.

Jesse Stewart, KRIB, Mason City contributed to this story.