Consumers can best protect themselves by having their furnaces inspected regularly, he said.
Erickson said it was odd that the blast apparently flattened two homes side by side. Generally, if a house explodes, it will knock out the wall of the home next door, but not level it, he said. For that to occur, both homes would virtually have to have gas leaks that ignited at the same time, he said.
Schreiber added that gas explosions create an intense wave of heat that can ignite surrounding homes.
"It goes very quickly. It's just a 'whoosh,' you know, like if you have a gas stove or a grill where it doesn't ignite immediately and there is a whoosh sound. That's kind of what happens here, but at a much, much greater level. It's a quick event, not a lingering thing."
The NTSB said the natural gas lines inside the house would be under the oversight of the utility or the state. Citizens Energy spokeswoman Sarah Holsapple said the utility had found no leaks in its underground facilities in the neighborhood; the Indiana Utility Regulatory Commission had no comment Tuesday.
Glenn Olvey, 52, isn't sure what caused the blast that wrecked his home and vehicles. But he knows his family is fortunate to be alive. The blast hurled Olvey several feet and trapped him, his wife and one of their two teenage daughters when their roof collapsed.
"I have been through car accidents, I've been through motorcycle accidents, I've been through tornadoes. I have never, never had anything like that," he said.
Olvey said he and his wife, Gloria, have struggled knowing that the explosion killed Jennifer and John Longworth, just two doors down.
"We're alive for a reason," he said. "What it is, I don't know."
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