Making a smarter crash test dummy


While seat belts save lives, the straps can unintentionally maim and even kill young children in crashes.

In researching the problem, bioengineer Kristy Arbogast talked to automakers about devising restraints that would be safer for small, immature bodies.

"The response I'd get back was, 'We don't have the tools we need to design better child seat belts,' " said Arbogast, a traffic-injury researcher at Children's Hospital of Philadelphia.

What they needed was a smarter dummy for crash tests.
Now they have one.

Ford Motor Co. engineers spent three years working with experts from Children's Hospital, the University of Virginia, Wayne State University in Detroit, and the Japanese seat-belt manufacturer Takata Corp. to develop a simulated child abdomen that fits into the standard 6-year-old-size crash-test dummy.

For more than a decade, it has been clear that the abdomen is the second most commonly injured body area in seat-belted youngsters, after the head. With the abdominal insert, safety engineers can at last measure precisely what happens to this vital region in the average 4-to-8-year-old.

Next month, Ford will present the prototype to the Society of Automotive Engineers, the first step toward making it available to the entire auto industry, said Stephen W. Rouhana, Ford's senior technical leader on the project.

"We're going to take the prototype to the society's 'dummy committee,' " Rouhana said. He chuckled. "That sounds funny."

Technically, a crash dummy is an "anthropomorphic test device." Equipping one with an imitation kiddie abdomen may sound simple, especially considering that the industry already has come up with a pregnant version.

But simple it was not. The researchers had to parse the biomechanics of child seat-belt injuries. Then they re-created the injuries in an animal model. Finally, they built a gizmo that behaved like abdominal tissue - taking into account variables such as muscle tension.

Children's Hospital's 11-year-old Center for Injury Research and Prevention provided its internationally recognized expertise on crash injuries in children ages 4 to 8.

At those ages, Arbogast explained, youngsters are usually too big for toddler safety seats but too small for lap and shoulder harnesses. The lap belt, which rests on the bony pelvis of an adult, often rides up a child's cartilage-soft pelvis to the stomach. Children may add to this belly-binding effect by sitting on the edge of the seat because their legs are short.

"They scoot forward on the seat so their knees can bend comfortably," Arbogast said.

The shoulder belt tends to cut across children's necks, so they often put the annoying strap under an arm or behind the back.

To study the biomechanics of improper belt placement, poor posture, or misuse of the shoulder belt, Arbogast and colleagues crunched an accident database and conducted in-depth crash investigations. They found specific patterns of abdominal injuries.

The seat-belted children were either propelled forward head-first over the lap belt, or their pelvises slipped under it. The crushing force of the lap belt - or the lap and shoulder belts - variously injured the liver, spleen, pancreas, bowel, colon, bladder, ribs, even lungs.

"The belt would almost go right through the abdomen to the lower spine," said Arbogast, lead author of the study, published in June. "We saw several cases of partial paralysis. We also saw children with serious injuries in relatively minor crashes. The driver sustained only minor bruises."

Booster seats, previous Children's Hospital studies have shown, can reduce the risk of crash injury in 4-to-8-year-olds almost 60 percent. Thirty-eight states, including Pennsylvania, New Jersey and Delaware, now have laws requiring the transitional safety seats.

But it's not an ideal fix. Only about half of children who need boosters actually use them. And while boosters can improve seat-belt fit, the child's body remains inherently more fragile than an adult's.

With researchers armed with an understanding of the mechanics of injury, their next step was to figure out how much force would cause it. Many variables were involved, but the key question was: How deep and how fast does the belt have to crush the abdomen to do harm?

So they developed an animal model using a species that they determined was anatomically and developmentally similar to a 6-year-old human: a 2 1/2-month-old pig.

Tests approved by an ethics review board - the 47 pigs were anesthetized and then euthanized so they would not feel pain - revealed that life-threatening injury was unavoidable when the lap belt penetrated 70 percent of the abdominal depth at a rate of about 8 meters per second, said Richard W. Kent, the University of Virginia biomedical engineer who led that study.

The threshold for serious injury, they found, was 40 percent penetration of the abdomen at a speed of about three meters per second. This translated to a 50-50 chance of serious harm, such as perforating the (dead) pig's bowel.

When the researchers published the pig model of pediatric abdominal injury 14 months ago, auto-safety engineers were wowed.

"Our team was invited to give lectures in Japan, Korea and Europe," Kent said. "Everyone wants to have a way to do this testing, because restraint systems are getting so sophisticated."

Still, Ford's experts had to build the gizmo that would "feel" these forces as a human abdomen would. They invented a flexible silicone shell filled with liquid silicone and equipped with light sensors.

During a crash test, the seat belt compresses the shell, causing light-emitting sensors in three spots on the front to move toward light-receiving sensors at the back. These record the change in light intensity, which is then converted into the key indicators - the speed and depth of abdominal penetration.

"The sensors tell not only how severe the crash is, but how the seat belt deformed the abdomen and the risk of injury," Kent said. "A child could walk out of a fender bender with significant injury, or walk away from a serious accident with scratches.

"Until now, there was no way to predict."

Ford's Rouhana said he hoped that sharing the imitation abdomen with the industry in the coming months would give safety engineers "the ability to do out-of-the-box thinking" to create better restraint systems.

Arbogast, meanwhile, looks forward to sparing mothers from arguments like the one she has with her daughter, who at age 10 is still shorter than 57 inches - small enough to need a booster seat.

"She gives me a hard time every now and then," Arbogast said. "I tell her: 'This is what Mom does. She studies how to make kids safer. So you're stuck with it.' "

Source and more information: The Philadelphia Inquirer

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