Tom Canavan was buried alive at the World Trade Center site when the twin towers collapsed 20 years ago on Sept. 11.

He was on the 47th floor of the North Tower on a conference call in his boss' office when the American Airlines Flight 11 plane struck his building at 8:46 a.m.

Canavan and his colleagues from First Union, a brokerage firm, began to slowly descend the stairwells to safety, passing police, firefighters and Port Authority rescue workers on their way up to try to rescue wounded survivors. While they were trying to escape, a second plane hit the South Tower.

Canavan said he and four of his colleagues emerged in the area underground at the World Trade Center filled with shops. That's when the South Tower collapsed. Less than 30 minutes later, the North Tower would also fall.

"I remember yelling to the people in front of me or trying to yell anyway, to get in a doorway," said Canavan. "I don't know if I even got it out of my mouth when I felt the thump, thump, and then I was just smashed to the ground like a bug. Everything went dark."

His last thoughts were of his son's upcoming third birthday party, and how he would never meet the little girl his pregnant wife was carrying. Soon, however, he "started to taste grit in my teeth and I started to smell smoke and I said, 'OK, I'm alive'."

Canavan said he and a still unidentified man were saved because a large cement wall had fallen over them, creating a safe pocket in the pile of twisted steel rebar and debris.

They began the painstaking process of crawling and digging their way upwards through the rubble. After what might have been 20 minutes, they saw a little peephole of light and got their first breath of fresh air.

"I squeezed myself through the hole. I was scraped from head to toe. I was hurt and I didn't, I didn't feel a thing."

A few more minutes underground and he would have certainly perished when the North Tower collapsed at 10:28 a.m. While most of his coworkers also escaped, four died.

Canavan said his experiences on 9/11 have become his legacy.

"I'm part of 9/11; it's part of me," he said.

"There isn't a day that goes by that I don't think of something that day, whether it's a person, whether it's a noise, whether it's a plane flying low," said Canavan, who plans to attend the 20th anniversary ceremony.

"It'll never go away. I've come to terms with that. Where people use a phrase, 'get over it.' This isn't something you get over."

Reuters