A natural gas leak inside a home caused an explosion and fire that destroyed a north Seattle home and injured two residents, and has prompted the utility company to look for other leaks in a 5-square mile area, fire and utility spokesmen said Monday. A couple who lived in the house thought they smelled gas Sunday night but weren’t sure so they didn’t report it, Seattle Fire Department spokesman Kyle Moore said. "When they woke up this morning and smelled something, they were turning on things and `boom!’ - the explosion," Moore said.