One person was killed last month in an explosion at JJ's restaurant in Kansas City, Missouri.

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An explosion ripped apart a Kansas City, Missouri, restaurant last month

Pilot lights inside the restaurant's kitchen ignited the gas, a new government report says

The blast came after a gas line was ruptured nearby by a person laying cable

One woman died after getting trapped when the restaurant's roof collapsed

CNN  — 

A fatal explosion last month in downtown Kansas City, Missouri, was caused by the accidental ignition of natural gas vapors that had accumulated inside a popular restaurant, according to a report from a joint city-federal task force issued Wednesday.

An employee for a contractor laying cable hit a 2-inch gas line with an underground boring machine late on the afternoon of February 19. The explosion occurred about an hour later, killing one person and injuring at least 15 others.

At that time, authorities did not know what had caused the leaking gas to ignite, according to Rob Hack, chief operating officer of Missouri Gas Energy.

Wednesday’s report – from the Kansas City fire and police departments as well as the federal Bureau of Alcohol, Tobacco, Firearms and Explosives – answers that question.

After the gas line nearby was ruptured, firefighters asked employees at JJ’s restaurant “to put the flames out on the candles, stove and hot water heater” inside, said the report.

When queried after the blast by investigators, the restaurant’s manager acknowledged the initial request and said workers “only put the candles out and turned the stove off, but did not turn out the pilot lights for the stove or hot water heater,” according to the report.

The report also shed light on how one woman, a civilian, died after getting trapped when the restaurant’s roof collapsed.

At one point, flames extended more than 100 feet from the building’s roof.

The contractor, Heartland Midwest, did not have a permit for the excavation, Assistant City Manager Patrick Klein said days after the explosion.

Authorities were alerted a short time after the gas line was hit. City firefighters responded to the scene but left a short time later after being told by the utility company that everything was under control, Mayor Sly James said.

A Missouri Gas Energy employee showed up about 20 minutes after the initial call and, after some initial readings on gas-measuring devices, called for backup, Hack said. The utility’s employees then went into businesses asking people to leave and brought in excavating equipment to try to vent the pipe.

But while JJ’s restaurant closed early due to a natural gas smell, hostess Deidre Estes and other employees weren’t in a rush to leave, unaware of the danger they were in.

Then, Estes told CNN affiliate KCTV, “Boom! And everything was black.”