San Diego- It was a mystery that took roughly four hours to figure out for a section of a Paradise Hills neighborhood.

San Diego Fire and Rescue crews along with Hazardous Materials crews from both the city and county responded to investigate a gas odor in the 6200 block of Childs Avenue.

The primary odor seemed to linger in one area, but reports came in from a four to five block area, according to San Diego Fire and Rescue Deputy Fire Chief Perry Peake.

As a precautionary measure firefighters went door to door notifying residents to stay inside and not to start up their barbecues.

San Diego Electric and Gas crews spent hours poking sensors into the ground, around meters, and in the air with no results. Their primary thought on a potential leak surrounded the fact a construction company had been working in the street earlier in the day digging up and replacing sewer lines. It was believed crews may have accidentally broken an underground line and didn't realize it.

Finally, SDG&E brought in a specialized truck with a laser sensor able to detect 18 separate flammable gases up to two city blocks away, according to an SDG&E employee on site.

It was determined the gas was methane from the ground soil dug up earlier in the day. SDG&E crews assured the fire department and residents that non-flammable levels of methane existed and that there was nothing to be concerned about.

An SDG&E employee on site explained that the chemical added to natural gas that we've all become familiar with has a similar smell to decaying sewage that possibly leaked into the dirt surrounding the pipes over the years.

Deputy Chief Peake says the department always airs on the side of safety when it comes to possible natural gas leaks.