Natural gas has been ruled the cause of the Monday night explosion that left one man with third-degree burns and damage to his respiratory track.

About 8:25 p.m. Monday, 78-year-old Alex Saunders was blown partly out of his home at 825 Wilson Ave. as a result of the explosion that caused the apartment to go up in flames. Saunders was transported to Mary Greeley Medical Center, 1111 Duff Ave., and then later taken to the University of Iowa Hospitals and Clinics burn department in Iowa City, said Lt. Kevin Peterson of the Ames Fire Department.

Saunders remains in the hospital recovering from third-degree burns covering more than 50 percent of his body, Peterson said. His respiratory tract also was damaged. U of I hospital officials said Saunders was in critical condition Tuesday night.

Several of Saunders’ family members went to be with him.

“Some family members went over to Iowa City, but I don’t know who they were,” Peterson said.

According to a press release, doctors at University Hospitals told family members that the first 72 hours were critical for Saunders in determining his prognosis.

Pat Stoffel, grounds crewman for the Public Works Department, was cooking supper with his fianc‚ in an apartment just south of Saunders’ efficiency when it exploded into flames. He said the apartment shook and he wasn’t sure what had happened.

“We felt it more than we heard it. We waited a little while before we went outside because it was kind of eerie,” Stoffel said. “When we went outside, we saw it was engulfed in flames.”

A man was pulling Saunders from the flames and asked Stoffel for help, he said, and another bystander took the man’s spot and helped drag Saunders into the street.

“I ran in to get some water for the victim,” Stoffel said.

Stoffel said Saunders had suffered a lot of damage to his body.

“It was really bad, that’s all I can say,” he said.

Stoffel said Saunders was the only person living in the efficiency, but he thought there was at least one person home in the apartment attached to it.

Peterson said investigators had suspected Tuesday morning that a gas problem was the cause and confirmed later that day the most probable cause was a natural-gas fueled furnace leak and ceased investigations. The efficiency is completely lost, and damage estimates were $40,000.

“It’s an explosive gas, so that’s what caused the explosion,” he said.

Peterson said the leak occurred around Saunders’ wall-mounted furnace.

“I don’t know if he had inquired about the leak,” he said.