Among those who died was Justin Blake, 17, of Buckner, Ark., who taped about 300 sparklers together to build a "sparkler bomb" that exploded unexpectedly, NBC News said.
A sparkler -- a handheld wire that emits flames and sparks in assorted colors until it burns out -- can burn at 2,000 degrees Fahrenheit, as hot as a blow torch, said Dr. Andrew Sama, president of the American College of Emergency Physicians.
Sama said about 200 people per day visit hospital emergency rooms with fireworks-related injuries around the July 4 holiday.
"There's no such thing as completely safe fireworks," Sama said. "A few minutes of well-intentioned fun can result in lifelong disabilities."