Dr Emil Chynn says he was walking his dogs through New York when he saw the Twin Towers burning on September 11, 2001, prompting him to put his rollerblades on and rush to see what was going on.
Nearly 3,000 people died in the terror attack, in which aeroplanes were hijacked and flown into the World Trade Center, the Pentagon outside Washington, DC, and another crashed into a field near Shanksville, Pennsylvania.
Dr Chynn said he felt his medical skills would be put to better use helping victims at the scene of the attack, rather than waiting to treat them at the hospital. He quickly got to work on what he says was the first triage centre on site.
Now 50, the doctor has released a series of never-seen-before photographs taken from the week he volunteered at the scene, in a bid to show the kindness of strangers during such a devastating and terrifying time.