This Independence Day, protect your eyes. More than 2,000 people need medical attention each year for eye injuries caused by fireworks, and new research finds it's the projectiles themselves, rather than the blast, that cause most of those injuries.
In the new study, researchers used eyes from cadavers to find out, through high-speed video and pressure sensors, what happens when the human eye is subjected to the explosive power of fireworks. They found that the pressures involved aren't enough to injure the eye on their own, as previously had been believed.
That leaves the actual projectiles hitting the eye as the main source for the 2,100 or so eye injuries caused by fireworks in the United States each year. Most of these happen during Fourth of July celebrations.
"For the first time, we've been able to prove through this research that it's not the blast or explosion that is causing the injuries but it's some sort of projectile," study researcher Stefan Duma, a biomedical engineer at Virginia Tech, told LiveScience. [10 Fiery Fireworks Facts]
In any explosion, the first danger comes from the shock wave, which can cause severe internal injuries due to sudden changes in pressure. It had been suggested that fireworks can create shock waves strong enough to internally injure the eye, Duma and colleagues wrote in the July 3 issue of the Journal of the American Medical Association.
The study is part of a larger Department of Defense effort to examine the injuries associated with explosions such as those from improved explosive devices (IEDs). Before building up to those sorts of large explosions, though, Duma and his colleagues started with small charges so that they can look at how damage changes as explosions grow in size.
The researchers set off 10-gram (0.35 ounces) charges of gunpowder at increasingly close distances to eyeballs removed from dead people who had willed their bodies to science. These charges were made to mimic the blast of commercial firecrackers like the "Bunker Buster" or the "Dixie Dynamite." Blasts were tested at 8.7 inches, 4.7 inches and 2.8 inches (22 centimeters, 12 cm and 7 cm) from the eyes.
After the tests, the eyes showed no internal injuries. In fact, the only damage was some minor corneal abrasion, caused by gunpowder flung from the charges scraping the eye.
"It gives us solid scientific proof that if you wear goggles you can prevent these injures," Duma said. "Any kind of eye projection can defeat these kind of projectiles."
The study also suggests that fireworks such as bottle rockets, which are made to fly, are a bigger threat of eye injuries than nonprojectiles like fountains or sparklers.
Of course, nonprojectile fireworks cause an array of injuries to other parts of the body: All told, 8,000 or so fireworks injuries are treated at emergency rooms each year. More than half those injuries are burns, according to the U.S. Fire Administration. Hands and fingers are the most frequently injured body parts, and hand-held sparklers alone are responsible for 1,200 injuries a year.