Fifteen years after the Twin Towers fell, Kenneth Summers still finds himself looking up.
The 66-year-old New Yorker, who was badly burned on 9/11 when he was thrown from the lobby of the North Tower as the hijacked American Airlines Flight 11 hit the building, says he scours the skies for airplanes and braces for the earsplitting noise he dreads when one is near.
“The sound of the second plane striking the building … it must have been a real whining, high-pitched sound that right to this day goes through me like a knife,” he says.
Summers, who worked on the 27th floor of the North Tower as a systems analyst for Empire Blue Cross and Blue Shield at the time of the attacks, was among four terror attack survivors who recently recounted their experiences in a series of emotional interviews with TIME ahead of the 15th anniversary of 9/11.
They include Michael and Anjali Pollack, a married couple who were at the Taj Mahal Hotel in Mumbai, India in 2008 when the hotel came under attack, and Fatih Kiyak, who was among hundreds of protesters at a peace rally outside of a railway station in Ankara, Turkey in 2015 when two bombs exploded nearby.
The four survivors say their stories are important to tell in the wake of high-profile terror attacks in Western Europe over the past year and several mass shootings on American soil, including the worst in U.S. history when a gunman killed 49 people at a Florida nightclub in June.
After 9/11, terrorist attacks around the world escalated, and at the peak in 2014, more than 30,000 people globally were killed, according to the U.S. State Department and the Global Terrorism Database. But in 2015, there was a significant drop in the number of attacks and casualties, the groups say. Neither organization has recent figures, but preliminary statistics gathered by IHS Jane’s Terrorism and Insurgency Center show a global decline.
Each of the survivors who spoke to TIME had a different experience, but they all agreed on the need to keep living, even in the face of fear.
“Whatever happens, life is going to go on,” Kiyak says. “You live anyway. What doesn’t kill you makes you stronger.”