Shell–and–mortar–style combustibles caused nearly 40 percent of fireworks–related injuries resulting in hospitalization, according to the study, published in The American Journal of Emergency Medicine.

Shells are spherical aerial explosives designed to be manually thrown or launched from a tube, called a mortar. Shell–and–mortar fireworks are legal under federal and Washington state law.

Every year, about 10,500 people are treated in emergency departments for fireworks injuries, according to the U.S. Consumer Product Safety Commission. This number has remained relatively unchanged since 1999. However, little data exists on severe fireworks injuries that require hospital admission.

The study reviewed the cases of 294 people admitted to Harborview Medical Center for severe fireworks injuries from 2005 to 2015. Patients’ mean age was 24, and males accounted for 90 percent of injuries. Among adults’ fireworks injuries, 98 (86 percent) involved shell–and–mortar explosives. The majority of children’s injuries came from rockets; teens sustained most serious injuries from homemade fireworks.

In many cases, severe injuries required multiple surgeries and caused permanent impairment, such as limb amputation or vision loss.

The study’s lead author is Dr. Brinkley Sandvall, a plastic surgery resident at the University of Washington School of Medicine. Harborview’s annual surge of emergency–department patients around the Fourth of July spurred her interest in fireworks research, she said.

“We treated about 30 patients for hand injuries requiring surgery during the July Fourth weekend last year,” she said. “This firework injury study is an excellent example of how real–world injuries treated at our trauma center contribute to our knowledge of injury causes and prevention,” said co–author Dr. Monica Vavilala, director of the Harborview Injury Prevention and Research Center (HIPRC). “The next step is to apply our new knowledge to health practices, policy decisions and individual behavior.”