AUGUSTA — Confusion about who owned a natural gas line where an air leak blew off a manhole cover Tuesday night has highlighted a predicament of having two competing firms install pipelines in the city.

There are now 18 city streets where Summit Natural Gas of Maine and Maine Natural Gas are allowed to have pipe, according to a Kennebec Journal review of city records.

The leak Tuesday night on Arsenal Street was later determined to occur in a section of Summit Natural Gas of Maine’s pipeline south of the old MaineGeneral Medical Center building. No one was injured, but for most of an hour the incident had city fire crews and police treating the line as if it were gas-charged and potentially explosive.

They called both Summit and Maine Natural Gas to send crews to the scene without knowing for a time exactly whose pipeline had failed. The city said Tuesday it would be improving record-sharing with first responders on the companies’ lines.

City records show both companies are allowed to have pipe on Arsenal Street, one of 18 streets they’re both approved for, along with Western Avenue, Civic Center Drive, Sewall Street and other well-traveled roads.

Maine Natural Gas, which turned on its pipeline in late October, called attention to the confusion that could create in an emergency earlier this year. Summit’s network hasn’t been powered up with gas, but the company has said it wants to turn it on by mid-December.

On Wednesday, Michael Duguay, Summit’s director of business development, said the air leak occurred because an improper cap fitted to the end of the section of pipeline on Arsenal Street was blown off during an air pressure test of the section. Companies test capacity of the network by pumping air in past the pressure level necessary to carry gas, holding it for hours.

“If the pressure drops at all, then you have to go back and do some remedial work,” said C. John Meeske, a Massachusetts energy consultant who was hired earlier this year by Augusta to examine the city’s natural gas market. “In this case, it became easy to see where the remedial work needs to be done.”

Duguay said the cap will be replaced and the section re-tested before the pipeline is turned on. “This is exactly why you’re required to do the test,” he said.

The leak was reported at 9:18 p.m. Tuesday, and witnesses said they saw steam coming from the opening. Augusta Fire Department Battalion Chief Daniel Guimond said that was likely dust from the wrecked pavement, but he said the hole “was roaring like a jet engine” from air pressure when he arrived.

Just before 10 p.m., an Augusta police sergeant said natural gas companies were telling police that the affected pipeline was Summit’s, but that was still “to be determined.” It was confirmed minutes later, and a Summit official was at the scene around 10:30 p.m. After a brief evacuation of apartments within 200 feet, authorities let residents back in around 10 p.m.

Lesley Jones, Augusta’s public works director, said she was “not sure why” authorities initially didn’t know whose pipe was whose on Tuesday night, “because Public Works knew.” But Jerry Dostie, Augusta’s street superintendent, said at the scene the city has plans on file that show where each company has pipe, but those plans are “not easily accessible” in an emergency.

Fire Chief Roger Audette said while the confusion may have delayed the response from Summit, it didn’t change his department’s responsibility, mainly to shut down the affected road and help police evacuate nearby residents, if necessary.

On Wednesday, Jones said as a short-term solution to Tuesday’s issues, the public works department will soon give city emergency dispatchers a list of the streets where each company is allowed to install pipeline, separated by company. Later on, she said the city will work to add locations of the companies’ pipeline networks to the Greater Augusta Utility District’s geographic information system, which already shows water, sewer and stormwater lines district-wide.

Audette said because first-responders didn’t smell mercaptan — the smelly substance added to otherwise odorless natural gas so leaks can be detected — they didn’t think it was initially a gas leak. Still, he said, the department “erred on the side of safety on the chance that they didn’t add mercaptan” and it was a leak.

He and Jones said in the near future, if a problem is found with a line in the city, both companies will be called to respond. That’s a unique problem for Augusta in the Kennebec Valley: Only Summit will serve the rest of the area, making the job easier for Bob Gilchrist, Waterville’s public works manager.

“I think one of the problems with Augusta is they have two companies servicing them,” he said. “There’s no question of ownership here” in Waterville.

Pipelines are thought of as safer ways to transport oil and gas than train or truck. But when there are problems, they can be deadly.

A 2012 investigation by ProPublica, an online news outlet, found that nationwide since 1986, pipeline accidents killed more than 500 people, injured more than 4,000, and caused almost $7 billion in property damages. In 2010, a San Bruno, Calif., natural gas pipeline ruptured underground, exploding a gas station. The blast sent flames hundreds of feet in the sky, left a 72-foot-long crater, killed eight and injured more than 50.

In 2011, the U.S. Department of Transportation said in all significant pipeline incidents from 2006 to 2010 in the country, the top three causes were material or weld failures, corrosion and excavation damage.

In January, when Summit got approval as a state utility, Daniel Hucko, a spokesman for Maine Natural Gas, which opposed Summit’s pipeline approval, warned of confusion between the two companies in an emergency, saying “if there is a problem with one of the lines, and there is a leak, there could be confusion and delays in getting that corrected” with two companies operating in close proximity to one another.

On Wednesday, Hucko said, “We witnessed some of that last night.” But he said when crews from his company arrived at the scene Tuesday, they could quickly tell it wasn’t their pipe, which runs south down Arsenal Street, but turns up East Chestnut Street about 400 feet from Summit’s affected area.

However, he said there are other spots where the companies’ lines are buried closer together. In an emergency, he said that could affect how quickly companies respond, “with the potential to create confusion.” But Hucko said crews from both companies will continue to respond to emergencies and control situations.

“Potentially there can be some issues,” he said. “But it’s really very safe and we want to keep it that way.”

Staff Writer Jesse Scardina contributed to this report. Michael Shepherd — 370-7652 [email protected] Twitter: @mikeshepherdme