Today, he's a Transportation Security Administration agent guarding the flying public from another attack using airplanes. But with the 11th anniversary of the attacks upon us, Brennan doesn't ponder how different his life is as much as he worries about his son, Alex, who's 24, and a lieutenant with U.S. Army and fighting in Afghanistan.
"My wife and I hope he and his men come home safe, whenever that may be," Brennan said Monday.
The federal government created TSA after the Sept. 11 terrorist attacks to harden the U.S. transportation system. Congress in November 2001 gave the agency authority over hiring and training security officers to work at the nation's commercial airports and for screening checked luggage for explosives.
There are 1,100 TSA employees working at LaGuardia Airport now, about 450 of whom were hired after the terrorist attack, said Dan Ronan, TSA federal security director at the airport.
Brennan, part of a group of TSA workers who met with the media on Monday to talk about how the terrorist attack changed their lives, said his son was a student at Stuyvesant High School, just four blocks from the World Trade Center, when terrorists flew jets into the Twin Towers.
"Physically, he was OK," said Brennan, 59. "But it had quite an effect on him."
At first Brennan said he and his wife, Lisa, a New York City schoolteacher, noticed their son expressed fear about what he witnessed as a 13 year old on Sept. 11, 2001.
And later, when their son wrote his college application essay, he spoke about wanting to "give something back," Brennan said.
"He wanted to face his fears," Brennan said about his son, who joined the ROTC while a student at Stony Brook University. "This was one way he chose to do it."
At the TSA offices near LaGuardia Airport, other workers, like Alfred Burgess, an air marshal, shared their stories. In the months before the terrorist attack, Burgess was one of about 30 air marshals, and was seriously considering retiring. He had been an air marshal since 1990, he said.
After Sept. 11, 2001, Burgess, of Rosedale, said it was obvious that the country needed people with his experience more than ever. Today there are thousands of air marshals on the job.
"I was proud," Burgess said, "to do my job."