Firefighters responding to reports of a fire on board the U.S.S. Miami Wednesday encountered a hellish atmosphere of intense heat and heavy smoke, two shipyard firefighters said Thursday.

The two, Assistant Shipyard Fire Chief Glenn Whitehouse and Firefighter Dan Tice, said each crew sent into the sub had only a few minutes to deal with the fire before they had to pull out and be replaced.

They said it took time and effort just to get through the narrow maze of submarine hallways to get to the forward section of the ship where the fire was burning. The hallways were so narrow it was difficult for firefighters to pass each other.

Then the heat and dwindling oxygen in their air packs forced them to leave and be replaced by another crew.

“That’s why the guys were taking a beating,” Tice said. “We went through probably 75 shifts like that.”

Navy officials won’t be able to enter the fire-damaged portion of the U.S.S. Miami for a few days to determine whether the submarine is salvageable, Rep. Chellie Pingree, D-Maine, said Thursday outside the Portsmouth Naval Shipyard.

Pingree, who visited the site of the nuclear submarine fire today, was briefed by shipyard officials about the fire which broke out late Wednesday afternoon and was not brought fully under control until early this morning.

“The ship is starting to cool down, so they’re pumping some air inside,” she said, ventilation which Pingree said is necessary before investigators can enter.

Area fire companies helped shipyard firefighters with the blaze. Seven firefighters were injured but all were treated and released.

Whitehouse said the shipyard’s fire crew numbers just 39 firefighters. With local fire departments helping out, he said there were about 100 firefighters dealing with the blaze on the Miami. Each crew of municipal firefighters was accompanied by a shipyard firefighter, to help them find their way through the darkened sub, he said.

“Our hats are off to them,” Whitehouse said. “If it weren’t for them…they were our saviors.”

Pingree said shipyard officials told her that many of the submarine’s critical systems had been removed as part of a lengthy overhaul prior to the fire. The submarine is in the third month of a 20 month overhaul.

Navy officials said the ship’s nuclear reactor was not in danger and a crew remained on board on that part of the ship to make sure that it stays secure.

Whitehouse said when he first arrived at the Miami, there was some light smoke coming out of the submarine and a ship’s crew had been dealing with the fire. Navy officials say they don’t yet know the cause of the fire but said there were no arms on board and its reactor – towards the rear of the ship – was shut down.

Whitehouse said his firefighters located the fire in the front of the sub and on the middle deck of the submarine’s three decks, but it quickly spread to the upper deck. At one point, flames were shooting out of the forward hatch.

Crews on the deck, dealt with those flames, he said, while crews inside the submarine continued to rotate in and out.

“It eats up a lot of time and energy and you can only advance so far,” Tice said.

Pingree praised firefighters who she said “kept going back into a burning ship.”

“It just sounds terrifying to me,” Pingree said. “We can imagine how terrifying it is for a firefighter to go into a burning house, but this is a burning cylinder.”

Shipyard officials told her that some firefighters went in and out of the sub more than 80 times over the 10 hours they fought the fire, she said. Firefighters could not spend long inside the submarine because their air supply was limited and the heat was intense, requiring many firefighters to make many trips inside.

It took hours to extinguish the blaze, but Whitehouse said, “we got into a rhythm” and eventually the flames were pushed forward ahead of the forward hatch and fire crews were able to drop a hose down from there, which was a crucial step in controlling the fire.

Before that, they had to thread fire hoses through narrow hallways.

Tice said the shipyard’s firefighters constantly train for ship fires “but certainly this is the most extreme” conditions encountered.

“It’s every emotion you can think of,” Whitehouse said. “You’re jacked.”

Pingree was not allowed inside the submarine and said there is no damage visible form the exterior. She said Navy officials are pretty sure where the fire began but told her they still don’t know the cause.

If the ship is able to be repaired, it’s in “a very good place” because the shipyard is one of the Navy’s leading submarine repair facilities, she said.

“That’s a $900 million piece of equipment that we need back on line,” Pingree said. “Hopefully, they can put it back together.”

Pingree is married to S. Donald Sussman, majority share owner of the Portland Press Herald/Maine Sunday Telegram, Kennebec Journal and Morning Sentinel.