BANGOR – In a matter of milliseconds, power generators throughout the state could have gone off line Thursday night and Maine could have been a part of the biggest blackout in the country’s history.

That didn’t happen, of course, but the possibility of that happening is real. Power generators throughout the state, all managed by computers that are monitored by humans, could have turned themselves off because they sensed a problem somewhere else in the interlocking North American transmission system.

“I think it would be irresponsible to say that it couldn’t happen here,” Stephen Diamond, a commissioner at the Maine Public Utilities Commission, said Friday.

The cause of the power outages that affected 50 million people in New York, the Midwest and parts of Canada had not been determined Friday night. But for a split second Thursday night, the computers that keep tabs on the transmission lines and power generators throughout North America each stood at the proverbial “fork in the road” – either shut down completely or isolate itself from the problem.

Maine was unaffected because computers throughout New England chose the right prong.

“The system worked well,” said Phil Lindley, a PUC spokesman. “It worked for [New England] and it worked for Maine perfectly. The question is why didn’t it work for the rest.”

In what’s being called a “cascading effect,” one computer picked up the initial but still unidentified problem on the transmission grid and rerouted electricity from one power generator over the lines to another part of the grid. In nine seconds, power generator after power generator, transmission line after transmission line, all believing that they could overload and break down, instead shut themselves off.

“My job is to see that this didn’t happen,” said Michehl Gent, president of the North American Electric Reliability Council, in a conference call with 800 reporters and energy officials Friday. “You can say I failed in my job.”

NERC is responsible for ensuring the reliability and performance of the nation’s power systems, according to its Web site.

In most of New England, similar computers that perform the same duties as those in the affected areas took another path. They chose to protect the region by cutting ties to the troubled transmission lines and forming “an island of isolation” from the troubled spots, according to energy officials. Power generated within New England stayed in New England.

In Halifax, Nova Scotia, in the control room of Nova Scotia Power, engineers and systems operators watched in amazement as the blackout unfolded on monitors in front of them, said Margaret Murphy, a spokeswoman for NS Power.

“Our operators could see the fluctuations and see the corrections,” Murphy said. “As we saw [Thursday night], the system worked.”

She said the computers noticed the outages and disenfranchised Nova Scotia – and even Maine – from the problem in “milliseconds, before a human operator would even have a chance to assess the situation.”

If the power outages had rippled throughout Canada into Nova Scotia and New Brunswick, they might have entered Maine through a transmission tie-line that connects the state to New Brunswick’s power grid. The line, located near Vanceboro, is managed by Bangor Hydro-Electric Co. and New Brunswick Power Co. Bangor Hydro and Nova Scotia Power are owned by the same parent company, Emera Corp. of Nova Scotia.

Murphy said that if the outages had reached the provinces, and the problem were detected quickly enough, Emera could have been able to stop the problem from entering Maine by literally severing the tie between the state and New Brunswick. And if the problem were in Maine, Emera could have stopped it from entering New Brunswick.

“We can do that from our own control centers,” said Murphy, adding that Mainers still would have power, that electricity just would not flow across the border.

Cutting off Maine from the rest of New England, from a tie-line that runs from York County into New Hampshire, would not be as easy, according to Dominic Slowley, a spokesman for ISO New England, a nonprofit energy management organization that oversees the region’s grid. It’s too intertwined with New Hampshire and Massachusetts, he said.

“Getting the tie-line from Canada shut off is not a problem,” he said. “Trying to isolate Maine from the rest of New England is problematic.”

Maine’s transmission lines are owned by three utilities – Central Maine Power Co., Bangor Hydro and Maine Public Service – but ISO New England controls the flow over them. From ISO New England’s control room, system operators and their computers decide whether to shut down generators and transmission lines in case of a problem.

Slowley said Friday that if a blackout were rippling from New York into Connecticut and the rest of New England, system operators would hurry to create an “island of isolation.” On Thursday night, parts of southwestern Connecticut were affected by the power outage, but the blackout stopped there. Only 2,500 megawatts of electricity were knocked off the New England grid Thursday and Friday. That’s a fraction of the more than 23,000 megawatts of power that was consumed Friday.

On Friday, state officials heralded one advantage that Maine has in comparison to other states – the power plants in the state produce more electricity than Mainers could use, so residents would be able to get by if the state were separated from the rest of New England.

Gov. John Baldacci, during an afternoon press conference, said, “Maine ended up being that kind of island of stability.” He said the ice storm of 1998 forced utilities to invest in its transmission lines “so that we can be strong and secure” if something like Thursday night’s episode were to occur.

“That isn’t to say there isn’t more work to be done,” Baldacci said, “and that doesn’t stop us from worrying about everybody else.”

He said all of New England’s governors need to have a more active role in the oversight of the region’s transmission grid, and that their involvement will be discussed at a meeting of the New England Governors Conference.

Lynette Miller, a spokeswoman with the Maine Emergency Management Agency, said her organization was “activated” Thursday night to stand on guard if the outages had spread to Maine. She said the state has a plan in place to assist residents if an outage occurs, but added, “You never know totally how ready you are until it happens.”