Dixon, IL – A natural gas explosion may have started the fire Sunday that killed a Dixon man and critically injured his wife in their home, according to preliminary findings from the state fire marshal’s office.

Office spokesman Louis Pukelis said Tuesday that the fire at 621 Garden Walk appears to have been accidental. It could take a few days or several weeks to make a final determination, he said.

Michael E. Nelson Sr., 61, died at the scene. His wife, Sherry Nelson, 57, was flown to OSF St. Anthony Medical Center in Rockford with severe burns. Her condition had improved from critical to serious as of Tuesday afternoon.

Dixon Fire Department is investigating the fire’s origin. Chief Tim Shipman said he suspects the explosion was in the kitchen, and the fire quickly spread to a portion of the basement.

There was moderate fire damage, along with smoke and water damage, to portions of the basement and kitchen, Shipman said.

Police and firefighters received a 911 call at about 12:40 p.m. It took about an hour to put out the flames.

Betty Dunne, a nurse who lives across the street, said Sunday that an unidentified woman in a yellow coat ran into the home after hearing the explosion and helped Sherry Nelson, who was taken to Dunne’s home to wait for an ambulance to arrive.

Firefighters pulled her husband from the home.

Sherry Nelson told Dunne that she and her husband woke up and went to the kitchen; he lit a cigarette and the explosion occurred, Dunne has said.