Tucson, AZ- David L. Teibel, Tucson Citizen – A midtown man remains in critical condition at St. Mary’s Hospital where he is being treated for burns sustained Friday in an explosion in his home.

Arnold Valenzuela, 44, is in the hospital’s burn center, said Sgt. Kerry Fuller, a police spokeswoman. He was burned when, in lighting a cigarette, he unknowingly ignited leaking natural gas.

During the holiday weekend, residents of three surrounding duplexes that were evacuated after the explosion and subsequent fire were allowed back home, Southwest Gas Corp., spokeswoman Libby Howell said yesterday.

Southwest investigators found the leaking line and had it repaired and service restored late Friday, she said. They found a hole in a plastic, 2-inch main line in an alley 50 to 60 feet from Valenzuela’s apartment.

That section was cut out and sent to a lab to determine what caused the hole. It was inspected about a year ago, and “it was fine,” she said.

The family in the other duplex apartment in the 1800 block of South Campbell Avenue is staying in a hotel until the apartment can be repaired, Howell said. The family was not home at the time of the explosion.

Because natural gas is lighter than air, when a line leaks, the gas will go through cracks in soil and even building foundations, she explained.

Gas leaks leading to explosions and fires are rare in Tucson, Howell said. Southwest Gas employees find two to three leaks a day at homes. There are about 600 gas-line breaks a year here, nearly always caused by construction work, she said.

After the explosion, Valenzuela ran from the building engulfed in flames, which were put out by neighbors, the Tucson Citizen previously reported.

The 3:30 p.m. explosion bowed window frames in the apartment and lifted the entire duplex roof. The subsequent fire spread through the duplex’s attic.