Butte, MT – Natural gas leaking from a supply line is what caused an explosion here Sunday that seriously injured a retired priest, fire marshal John Lasky said Monday.

The blast was ignited when the Rev. Jim McCarthy, 71, tried to light a cigarette while taking a bath in his four-plex apartment building, Lasky said.

McCarthy was taken to St. James Healthcare with burns on his head, arms and legs. He was later transferred to University Hospital’s Burn Center in Salt Lake City. He was listed in critical but stable condition Monday.

Lasky determined that gas leaked from a line behind McCarthy’s brownstone and seeped through the ground, possibly following buried pipes into the building.

He believes the gas then rose to McCarthy’s bathroom through cracks and holes drilled for water lines and other utilities, exploding when McCarthy struck a match to light a cigarette.

The explosion blew out the second-story back porch of the brownstone four-plex at about 9:15 a.m. Sunday, and thick smoke filtered across the neighborhood. The building is one block east of Butte Central Elementary School.

Neighbors wrapped a blanket around McCarthy, who apparently was alone in the building, and walked him down the stairs from his apartment. He suffered burns on 40 percent to 50 percent of his body.

Lasky said McCarthy and his neighbors smelled gas more than 16 hours before the explosion. However, they didn’t report the odor to authorities.

“Nobody notified us or the power company,” Lasky said. “We could have went and hopefully we could have located the source of the natural gas. This could have been prevented so easy by someone making a call that night.”

The Butte-Silver Bow Fire Department and the Boulevard Volunteer Department responded to the blaze.

Claudia Rapkoch, NorthWestern Energy spokeswoman, encouraged anyone who smells natural gas to immediately contact the company.

“That is one of our highest-priority calls,” she said.

People who smell gas or hear a suspicious hissing sound should leave the area and use a neighbor’s telephone. Using a home telephone could create enough of a spark to cause an explosion, Rapkoch said.

“Don’t turn anything on, and call us from a safe location,” she said.