Fire Lt. Martin Fullam survived the Sept. 11, 2001 attack on the World Trade Center — a firefighter who rushed to ground zero on his day off and dived into the smoking debris in search of life.

It wasn't until four years later that he nearly died, as he gasped for air, barely able to speak or move. But on Wednesday, Fullam left a Manhattan hospital with a new lung and a renewed spirit.

Although he can now walk on his own, his body is weakened and he was in a wheelchair as he emerged from New York Presbyterian Hospital at Columbia.

Dozens of firefighters lined up on both sides of Fullam as he rolled toward a waiting van to the sound of bagpipes, accompanied by his wife, two daughters, hospital staff and the surgeon who performed the transplant.

"I really feel like the luckiest man in the world," the 56-year-old career firefighter said at a news conference minutes earlier, through a mask protecting him from infection.

"I know it stinks to get sick, but I am enjoying one of the best parts of my life," he added. "I'm going to go home and spend time with my wife and kids."

Doctors cannot absolutely prove that the fire lieutenant's lung disease is a direct result of working in the contaminant-filled air of ground zero following the terrorist attack.

Fullam developed polymyositis — a rare autoimmune disease that attacks the body's tissues, said Dr. David Prezant, the chief medical officer for the Fire Department's Office of Medical Affairs.

Generally, only 1 in 100,000 people have the disease.

Fullam was off the morning of the attacks but quickly gathered a group of firefighters who took the Staten Island Ferry to lower Manhattan. They entered the destruction without masks or protective gear.

"He was there when New York City needed him," Prezant said.

A healthy man, Fullam spent six months sifting through the toxic debris.

In 2005, he was found to have polymyositis and pulmonary fibrosis, both of which his doctors have blamed on his 10-hour days in the pit.

Now, he's off oxygen for the first time in more than three years. The 27-year fire department veteran who worked at several city firehouses, including Ladder 87 on Staten Island in 2001, is getting disability benefits. He says he doesn't know whether he'll be able to work again.

The transplant costs were covered by the federal government, and the lung came from a stranger through the New York Organ Donor Network, a nonprofit that coordinates organ and tissue donations in the New York area.

Doctors believe that after therapy to regain his strength, Fullam should be able to lead a fairly normal life. Lung transplant recipients at New York-Presbyterian have a 90 percent survival rate the first year that drops to about 60 percent by the fifth year.

On Wednesday, Fullam looked no further than his new life now: "I just want to go home."