"We just stood there and watched, to our horror, the second tower come down," Hayden says. He then joined a group of 20 doctors from the conference who volunteered to help out at a makeshift hospital converted from a skating rink.
"There were quite a few stretchers . . . and about 150 doctors already there," says Hayden.
People arrived with medical supplies, food and water, but Hayden says an eerie calm descended as doctors prepared to receive injured victims in the thick stench of smoke.
"We waited four hours," recalls Hayden, "and in that time we didn't see a single patient pulled out." Relief efforts were stalled by the unsteady wreckage of the collapsed buildings, but there was no shortage of helping hands.
"The only people we could see were the many, many volunteers," says Hayden. The Red Cross set up a blood bank, and the lines were miles long. As police began cordoning off the streets, says Hayden, they saw many people walking north, out of the city.
As he witnessed the collapse of Tower 7 of the World Trade Centre, he finally came to grips with the degree of devastation he was dealing with. People who suffered small injuries -- abrasions, broken arms and legs -- were brought to hospitals, leaving doctors in charge of triage and trauma care on constant stand-by at the rink.
"Initially we just hoped," he says. "As the day went on, we realized that there were going to be very few survivors."
Hayden echoed what many have described as a surreal feeling as the events unfolded.
"There were moments, particularly as I was standing there in this rink, when it felt like a movie set," he says. "We felt the spirit of New Yorkers coming together. It felt like a family."
On his way down to the rescue site, Hayden saw owners of street-side delis putting out sandwiches and water.
As he left the city, Hayden was still overwhelmed by the fear and uncertainty that came with the experience.
"Life is changed," he says. "It was fear, terrible fear, that another building was going to go down. We looked up into the sky and saw fighter jets, we looked at tall buildings in a different way...I'm not sure. We just feel nervous, shaken."