WASHINGTON (Reuters) - On the morning of September 11, 2001, Patrick Smith was walking toward a television set in a Pentagon office to get news of the attacks on New York's World Trade Center when he heard a loud boom.
"The wall in front of me kind of buckled inward," he recalled. "The ceiling tiles and wires all started coming down, then it went black and then ... a giant fireball just came over the wall."
Such scenes will pass through the minds of many survivors on Thursday, when the first major permanent U.S. memorial to commemorate the September 11 attacks will be dedicated to the 184 victims of the assault on the Pentagon.
The ceremony at the fortress-like headquarters of the U.S. military, attended by President George W. Bush, will take place exactly seven years after al Qaeda militants hijacked four airliners and killed almost 3,000 people.
Smith, a civilian who works for the U.S. Army, will be in the audience. He knows he is lucky to have that opportunity.
"I could hear and feel the hairs on my head and on my arms just starting to singe, just from the intense heat of the flame," he said. "If I'd walked six feet further, then the chances are I wouldn't be sitting here talking today."
Smith saw a colleague in the flames but she was unable to get out and he was unable to help her. A male colleague came running out of the flames, his clothes on fire.
Smith dived to the floor and crawled away from the inferno. He took the hand of a wounded colleague and together they found their way to safety.
"She had second-degree burns and the skin was actually starting to peel off her face," he said.
The memories have become less intense over time but will never fade completely, Smith said.
He believes the memorial park at the Pentagon created by New York-based designers Julie Beckman and Keith Kaseman, which features maple trees, light pools and a bench to commemorate each victim, is a fitting tribute to those who died.
"They did a great job with it," said Smith, who was working in the Army's personnel department at the time of the attack.
Smith said there was a thought in the back of his mind that the Pentagon, a major symbol of U.S. military power, could be targeted after two planes slammed into the World Trade Center.
That idea came to the front of Army Sgt. Jessica Walker's mind after watching the scenes from New York on television.
Walker recalled telling a colonel in her Pentagon office: "You know what, ma'am? We're just as vulnerable."
Right at that time, Walker said, two other colonels came running out of a neighboring office and one exclaimed: "Oh my God, a plane is going to hit the building."
The colonels must have seen the plane through a window, Walker said.
She jumped over her desk and heard a loud bang as American Airlines Flight 77 from Washington's Dulles Airport crashed into the building at 9:37 a.m.
The attack killed 125 people in the Pentagon, along with the plane's 59 passengers and crew and the five hijackers.
Walker and her colleagues ran down a hallway to evacuate.
"During the whole process, it was kind of like an eerie, strange quietness," said Walker, who was working in the Army's logistics department.
"I know we were probably running as fast as we could but it just seemed like everything was going in slow motion."
Tom Van Leunen, a Navy public affairs officer at the time of the attack, also recalled the strange calmness.
"It was dead silent," he said. "It was such an eerie day."
After evacuating his office, Van Leunen spent the day helping television crews set up operations near the Pentagon.
When he went to take the underground railway home at night, he realized his wallet was still back in his Pentagon office.
"I had to ask, literally, this little old lady if I could borrow five dollars to get a metro ticket to go home," said Van Leunen, who retired from the Navy this year as a captain.
"I was covered in soot, in a Navy uniform and sunburned as heck from having been outside all day. And she looked at me and she just assumed that I'd come out of the building and she started crying and gave me five dollars."
Editing by Kristin Roberts and John O'Callaghan