A fire that started in a vacuum cleaner won't sink the USS Miami, which will be repaired at the Portsmouth Naval Shipyard.

Preliminary findings show that the fire that caused more than $400 million in damages to the submarine started in the vacuum cleaner used to clean the work site at the end of a shift, officials at the naval shipyard said Wednesday.

U.S. Rep. Joe Courtney, D-2nd District, said he was told by the Navy's senior leaders at Saturday's commissioning of the newest Virginia-class submarine that repairing the Miami is "going to be the path forward."

"We're not scrapping it," Courtney said Wednesday.

The shipyard did not provide any further details on the cause of the fire in its statement. It did say the repairs would be done at the Portsmouth, which means the work will not go to Electric Boat in Groton as members of Connecticut's congressional delegation had hoped.

The Miami (SSN 755) was in a dry dock at the shipyard for maintenance and upgrades when it caught fire at 5:41 p.m. May 23 and burned until 3:30 a.m. the next day. On Wednesday morning, the Portsmouth Naval Shipyard Fire Department responded to a fire alarm aboard the sub, but the shipyard later said it was a false alarm.

Courtney said he was told the Miami blaze started after burning embers in the vacuum ignited other refuse in the machine.

The first responders went to the wrong level of the submarine after an alarm sounded, giving the fire time to spread, said Courtney, who didn't know whether the alarm system or the first responders misidentified the level.

The Navy has estimated repairs to the sub at about $440 million, or a base of $400 million plus 10 percent due to the disruption of other planned work across all naval shipyards and the potential need to contract with the private sector.

That figure was already provided to Congress, Courtney said, since the Navy's shipbuilding budget is moving forward.

The investigation into the cause and damage assessment is ongoing. The Naval Criminal Investigative Service was looking into whether there may have been any criminal wrongdoing, such as arson, but Courtney said NCIS quickly determined there wasn't any and closed its investigation.

A spokeswoman for the Portsmouth facility said she could not immediately say whether the shipyard has changed its practices for how vacuum cleaners are used and stored there.

While the investigation continues, John Holmander, vice president of operations at Electric Boat in Groton, said he could only say that EB "takes all appropriate measures to ensure the safety and security of the workplace."

EB built the Los Angeles-class submarine for $900 million. It was commissioned at the Naval Submarine Base in Groton in 1990 and arrived at the Portsmouth shipyard in March for a 20-month overhaul.

The fire damaged the torpedo room, command and control spaces and berthing areas. The reactor had been shut down for more than two months at the time of the fire, and the nuclear propulsion spaces were not affected, according to the Navy. No weapons were on board.

A team from EB was at the shipyard Monday to help the Navy assess the damage. Courtney said he anticipates a "robust shuttle" of EB experts to the shipyard and expects some of the work that would've gone to the naval shipyard to go elsewhere, such as EB, while the yard is busy with the Miami.

The Navy is considering using parts from the USS Memphis, another Los Angeles-class submarine, to repair the Miami. The Memphis, a Groton sub, was decommissioned last year and is at the Portsmouth shipyard.

Courtney said he did not know how long the repairs would take but said it would be longer than the 20 months planned for the overhaul.

The shipyard's workforce has removed water from the submarine and installed lighting and staging. The Navy plans to award a contract for the detailed cleaning this week. Navy engineers are analyzing the hull, and the cost estimate for the repairs will continue to be refined, according to the naval shipyard.

U.S. Rep. Chellie Pingree, D-Maine, was the first member of Congress to go inside the submarine Monday.

"The Navy has been working full speed ahead to determine the cause of the fire and the extent of the damage," Pingree said in a statement Wednesday. "They've done a great job inspecting the boat quickly and efficiently and I'm confident we will have more detailed information about what's needed for repairs in the near future."

j.mcdermott@theday.com