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FIRESTONE, Colo. — The National Transportation Safety Board is looking into the April 17 home explosion and fire in Firestone that killed two men.

The explosion was caused by gas that entered the home through a cut, abandoned flow line from a well, investigators said.

Spokesman Keith Holloway said the agency will look to see if there are safety issues that could have a national impact.

Gov. John Hickenlooper called for a statewide review of oil and gas operations. Energy companies are inspecting pipelines that are attached to the more than 54,000 active oil and gas wells in the state.

Anadarko Petroleum, which owned the well near the Firestone home, closed 3,000 vertical wells in northeastern Colorado as a result of the explosion.

Great Western Oil and Gas also shut down some of its wells as a precaution.

Holloway said a typical accident investigation can take 12 to 18 months before a probable cause is determined.