New York ? They were trudging up the stairs of the north tower, weighed down with gear and pausing every four floors to catch their breath. They had no idea the south tower had been hit.

“It was single file, civilians going down and firemen going up,” firefighter Marcel Claes recalled. “The civilians were orderly and blessing us and helping the injured down.”

At the 35th floor, on his knees and talking with other firefighters about how best to get equipment up the tower, Claes and his brethren felt a rumble – like an earthquake, or a train going through your living room, he said.

It was then, as the south tower of the World Trade Center was collapsing in a giant cloud of rubble, that he heard the voice of a chief from another battalion: “Drop everything and get out.”

The story was just one that emerged Friday as the Fire Department released 12,000 pages of oral histories recorded by firefighters who responded to the trade center attack and lost 343 of their brethren. It is the most detailed portrait yet of the horror and chaos of Sept. 11, 2001.

There were stories of firefighters’ dramatic attempts to rescue civilians, of their decisions to evacuate on orders or their decisions to stay in the towers, of their sheer terror when the towers fell.

Sgt. John Sheehan, of Fire Patrol 2 in Manhattan, stands guard as occupants evacuate Tower One during the attacks on the World Trade Center towers in New York in this Sept. 11, 2001, file photo. The Fire Department of New York made public Friday 15 hours of radio transmissions and more than 500 oral histories recounting the rush to the twin towers that saved an unknown number of civilians and cost 343 firefighters their lives. Sgt. Sheehan escaped before the towers collapsed.

And they came in chilling detail. Firefighter Maureen McArdle-Schulman recalled hearing someone yell before the collapses that something was falling from the towers. She said she thought it might have been desks.

When she realized it was bodies – people jumping from the towers – she said she felt like she was intruding on a sacrament.

“They were choosing to die, and I was watching them and shouldn’t have been,” she said. “So me and another guy turned away and looked at a wall, and we could still hear them.”

The oral histories were made public along with hours of Fire Department radio transmissions, their release compelled by a lawsuit filed three years ago by The New York Times and long contested by the city.

Some of the material had been released before, and the records released Friday were unlikely to fundamentally change the understanding of the attacks that day.

Still, the histories offered a poignant catalog of what the firefighters there experienced, and the radio transmissions added new texture to the historical record, beginning at 8:46 a.m. with an urgent but calm description of a plane crashing into the World Trade Center.

“The World Trade Center tower Number One is on fire!” one firefighter radioed.

As the depth of the crisis became clear, the voices on the radios thickened with panic.

“Send every available ambulance, everything you got to the World Trade Center,” a firefighter calls from Engine 1. “Now!”

Family members of lost firefighters pored over the records Friday, some tearing up at descriptions and sounds of the attack and the response. At an office building in midtown Manhattan, a half-dozen family members and two fire officers bent over laptops to examine the material.

“It’s very emotional. It’s very difficult,” said Sally Regenhard, mother of 28-year-old Christian Regenhard, who died along with most of his company’s firefighters. “But it’s no harder than knowing every day that my son is gone.”

Lt. Warren Smith recalled leading other firefighters up the north tower to the 31st floor when they received an order to evacuate. The building came down about a minute after he was outside.

He later tried to radio missing colleagues. The communications systems were working better, he said.

“At this point, the radio was pretty open because there weren’t a lot of survivors, really,” he said.