The blast or the projectile? Virginia Tech research illuminates fireworks-related injuries

Every year, as business picks up at pop-up stores and chain retailers selling fireworks to celebrate the Fourth of July, so do concerns about the injuries these explosives sometimes cause.

Of the approximately 10,000 fireworks-related injuries treated in emergency rooms annually, more than 2,000 involve damage to the eye. Researchers at Virginia Tech helped reveal the mechanism of those injuries, which can have a significant impact on the patient’s quality of life.

For years, most researchers thought that fireworks-related eye injuries were likely caused by what’s called blast overpressure: that the pressure wave unleashed by the explosion increased the pressure in the eye, causing bleeding and even rupture of the eyeball.  

Virginia Tech professor Stefan Duma wondered if there might be a different explanation.

Duma is the Harry Wyatt Professor of Engineering in the College of Engineering and the interim director of the Institute for Critical Technology and Applied Science. An expert in injury biomechanics, Duma suspected that the eye injuries caused by fireworks might not be a result of the pressure caused by the blast, but the projectiles it released.

Knowing exactly how these injuries occur can help prevent them.

“Is it the explosion or is it the projectile? Because if it’s the explosion, then you need to change the force of the explosion. But if it’s the projectile, you can come up with protective strategies to shield the eye,” Duma said.  

Investigating the effect of explosions on the eye was familiar territory for Duma. He and his team had spent several years studying blast-related eye injuries among soldiers.

“We had done a lot of blast work for the military, where we were looking at eye injuries caused by that pressure wave. We applied those techniques to studying bottle rockets,” Duma said.  

Duma, assistant professor of biomedical engineering and mechanics Andrew Kemper, and a team of students simulated fireworks using gunpowder and measured the pressure inside and outside the eyeball. They also looked for signs of damage including corneal abrasions, scleral damage, and globe rupture.

That research, published in 2012 in the Journal of the American Medical Association, revealed that the injuries to the eyeball were a result of shrapnel released during the explosion, not the increase in pressure.

“We were able to show that it’s not the blast — it’s the projectile,” Duma said. “The pressure of the blast itself is too low at that level to cause any eye injury.”

Duma’s work on eye-injury risk for a variety of applications resulted in the development of a specialized dummy headform embedded with sensors that measure the force experienced by the eye and the surrounding bones, and a better understanding of the quantitative relationship between those forces and the likelihood of serious eye injury.

His work with the military led to recommendations for protective eyewear for soldiers. It also launched research projects with toy companies, who sought Duma out to evaluate the eye injury risk of products like Nerf darts, water pistols, and lightsabers.

For fireworks, as in other applications, understanding the mechanism of injury can help encourage evidence-based regulations and protective gear. And in fact, states with laws restricting the use of projectile-based fireworks see fewer fireworks-related eye injuries.

Sometimes, of course, safety is a matter of common sense.

“Don’t shoot bottle rockets at each other,” Duma said.