Initially it was believed that as a man lit a cigarette in his garage on the 1900 block of Palomino Drive, it ignited fumes from old rags covered in paint thinner and caused the explosion.
But as crews were wrapping up the scene, Battalion Chief Brian Ruffentine with Gilbert Fire and Rescue said hazardous material crew began checking underground natural gas level in the neighborhood and discovered some abnormalities.
"The neighborhood itself does not have natural gas to it, but the adjoining one does" Ruffentine said. "We've got enough conflicting information from the metering that posed a question of whether or not we have got an underground gas leak."
Dozens of crews responded to the scene and began evacuating approximately 22 homes in the area near East Warner Road and South Val Vista, Ruffentine said. Southwest Gas is also responding.
"If we do have a gas leak we need to secure that before it'll be safe for the folks to get back in their house," he said.
The explosion now believed to be caused by the leak, was strong enough to blow the garage door off of the home and the man sustained severe burns, according to Ruffentine. He was transported to Maricopa County Medical Center and is in serious condition. So far no one else has been injured.