Pete Spall saw it all from a Verizon training center in Manhattan.
"You could see the smoke and everything. I actually saw [Tower] 2 come down,"
The next day, Pete became one of the 50,000 people who would work in and around Ground Zero.
His team spent 12 hour shifts restoring vital communications, especially to Wall Street.
"I was working 13 out of 14 days, and I was there 8 months," Pete said.
With all the dust at the site, he knew to use a breathing mask if he could and to stop smoking.
But his smoker's cough never went away, it got worse.
Dr. David Murphy of Deborah Heart & Lung Center says that's the World Trade Center Cough so many Ground Zero workers have.
He's seen dozens of those workers.
"We've seen everybody from people who just have a cough, to people who are very sick," Dr. Murphy said.
Pete came to Dr. Murphy after several frightening attacks.
"I would go from a tickle and a runny nose to my fingers being numb and not being able to breathe," Pete said.
The doctor says the culprit wasn't the dust you could see, but the tiny particles you couldn't.
Those go deep into the lungs, irritating and scarring the tiny airways which move oxygen in, and carbon dioxide out.
One year after 9/11, the breathing capacity of recovery workers at Ground Zero declined 12 times faster than a normal person does as they age.
Pete's COPD, or Chronic Obstructive Pulmonary Disease, is now under control with medication.
But it will always be with him, along with a small box of mementoes from his time at the World Trade Center. They include Pete's ID tags, a rivet snapped by the force of the crash, mangled metal still covered in dust, and small paper angels made by children in the Midwest for the Christmas tree at Ground Zero.
He hopes to find the makers, to thank them for their kindness.
Pete is proud he'll work in the new tower rising where the World Trade Center was. It's what he needs to heal emotionally.
"I'm going to be happy when I can see a building and a fountain going," Pete said.
The debate goes on about the extent of the health effects from the 9/11 attacks.
A clearer picture of some risks, such as cancer, won't be known for years.