As the plane burned, the 16-year-old Chinese student was buried by the firefighting foam rescue workers were spraying to douse the blaze.
And in the chaotic moments that followed -- flames devouring the fuselage, those aboard escaping by emergency slides, flight attendants frantically cutting away seat belts to free passengers -- a fire truck ran over Yuan, killing her.
The new details, released Friday by the coroner's office, compounded the tragedy for her family in the aftermath of the July 6 crash at the San Francisco airport that killed two other teenage girls from China.
"There's not a lot of words to describe how badly we feel, how sorry we feel," said San Francisco Fire Chief Joanne Hayes-White.
Yuan's family was upset after learning the details of their daughter's death and wants her body returned to China, San Mateo County Coroner Robert Foucrault said. "It was a difficult conversation," he said.
Hayes-White said she was trying to arrange a meeting with them and that the "tragic accident" would prompt a review of how the fire department uses the foam and responds to emergencies at the airport.
"There's always room for us to evaluate and improve our response," she said. "(There's) very unfortunate news today. However, many, many lives were saved, and we made a valiant effort to do so."
Online comments by Chinese citizens, while expressing sadness at the girl's death, praised the U.S. authorities for revealing the truth and contrasted that transparency with frequent cover-ups by their own governments.
Hayes-White said she did not immediately foresee any disciplinary action. San Francisco police and the National Transportation Safety Board are investigating.
Families of the three teens killed have hired a New York law firm to represent them, the San Francisco Chronicle reported Saturday.
Relatives of Yuan, the girl killed by the fire truck, issued a statement through their attorneys saying they were "devastated and heartbroken," the paper reported.
"She was their only child," said attorney Anthony Tarricone. "It's especially painful knowing that she survived the crash."
The third fatality was found alive her seat, but Liu Yipeng, 15, died at a San Francisco hospital on July 12.
In all, 304 of the 307 people aboard the Boeing 777 survived the crash at San Francisco International Airport.
Yuan and her close friend, 16-year-old Wang Linjia, who also died, were students at Jiangshan Middle School in Zhejiang, an affluent coastal province in eastern China, Chinese state media has reported. They were part of a group of students and teachers from the school who were heading to summer camp in Southern California.
Yuan and Linjia were seated at the back of the plane. Authorities say the jetliner came in too low and too slow, clipping its landing gear and then its tail on a rocky seawall just short of the runway.
Linjia's body was found near the seawall at the edge of the runway. It was unclear how Yuan got from the airplane to the spot where she died. Investigators believe she was down on the ground and not standing up during the "volatile" and "dangerous" aftermath of the plane crash, the fire chief said.
Foucrault declined to go into detail on how he determined the teenager was alive before she was struck, but said there was internal hemorrhaging indicating her heart was still beating at the time.
Authorities confirmed last week that Yuan was hit by a vehicle racing to extinguish the flames in the plane. Police said she was on the ground and covered in the foam that rescuers had sprayed on the wreckage.
Firefighting crews apply the foam not only to stop the fire and cool the fuselage but to suppress fuel vapors. They continue to spray it to maintain the blanket because it can break down under certain conditions, fire department spokeswoman Mindy Talmadge said.
Fire trucks usually start shooting foam while approaching the fuselage from 80 or 100 feet away. The foam is also used to clear a safe path for evacuees, experts say.
"This is very rare. I've never heard of it before. I'm not aware of any other similar incident in my 35 years in the fire service," said Ken Willette, a division manager for the National Fire Protection Agency, which sets national standards for training airfield firefighters.
Willette said that amid the chaotic scene that included a burning aircraft, hundreds of survivors running for their lives -- as well as those who needed to be rescued -- the firefighters' other primary objective was to put down a foam blanket to suppress the fire.
"Their training kicks in at a time like that, and they focus on what they see on scene," Willette said. "Their mission going into that operation was getting into the aircraft, to save as many lives as possible and avoid hitting any of the people who may have been going away from the scene.
"But for reasons unknown, the coroner has confirmed that this young lady who was in the area of the crash was run over by a fire apparatus. This was a very tragic accident."
Associated Press writers Mihir Zaveri in San Francisco and Didi Tang in Beijing contributed to this report.
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