When a car crash occurs, people with osteoporosis and
other brittle bone disorders often suffer more serious
injuries than others do. To better protect these "fragile"
motorists, three Johns Hopkins engineering students have
devised a harness and vest system that significantly
reduced impact forces when tested on a high-tech crash
The students were responding to a challenge from the
Center for Injury Research and Policy in the Johns
Hopkins Bloomberg School of Public Health.
"We estimate that as many as 13 million people with
osteoporosis, osteogenesis impefecta [brittle bone
disorder] and hemophilia need some additional protection
from forces applied to the torso during a car crash," said
Gary S. Sorock, an associate professor at the center. "The
assignment was to design and test a restraint system that
would reduce these forces, protecting the ribs and the
sternum in particular."
During their two-semester Engineering Design Project
course in the Department of
Mechanical Engineering, the team designed a vest filled
with three layers of foam padding, each with a different
density, to absorb some of the energy that causes a
motorist's chest to compress during a crash. In people with
weakened bones, this compression can lead to broken ribs
and other serious internal injuries. The students also
replaced a conventional three-point shoulder belt with a
four-point race car harness, which distributes the crash
forces across a wider area of the body and keeps the body
in a tighter fit against the seat.
The student inventors, all seniors, were
engineering major Richard Chen and mechanical
engineering majors Patrick Danaher and Ryan Lavender. They
were required to work within a sponsored budget of $8,000
but wound up spending only about $5,500 to produce the
crash protection system.
In May, the students brought their system to the
Impact Biomechanics Test Facility at the university's
Applied Physics Laboratory. The staff assisted the students
in conducting tests on a dummy that simulated a 108-pound
woman, belted onto a sled moving at an average speed of
18.5 mph. The dummy was equipped with sensors to gauge the
effect on various parts of the body during the equivalent
of a 20-mph head-on crash or a 35- to 40-mph crash
involving a moving car striking a parked vehicle. A
high-speed camera mounted on the crash sled captured
close-up images of the dummy as it was jarred by the
The students tested the dummy four ways: with a
conventional shoulder belt alone, with a shoulder belt and
their prototype foam-filled vest, with the four-point
harness alone and finally with both the harness and vest.
When the dummy was outfitted with the vest under the
conventional restraint, chest compression was reduced by
approximately 8 percent (from 26.9 to 24.9 millimeters).
Testing with the harness provided a different loading
mechanism to the dummy torso and created much less sternum
deflection (3.5 millimeters). Despite the reduced loading,
the addition of the vest further decreased the sternal
compression by 17 percent, to 2.9 millimeters.
The students also compared crash impact forces,
measured from the seatbelt. This dropped from 644 pounds of
force with the standard shoulder belt alone to about 436
pounds with the harness.
Andrew Merkle, an associate researcher at APL's
Biomechanics and Injury Prevention Office, supervised the
students' crash dummy tests.
About the results, Chen said, "We were happy to see
the reduction in blunt force upon the dummy using this
system. The vest might also have some applications in
helping to prevent injuries in sports like football or
Lavender agreed. "I think the vest has the potential
to help a much wider audience than I originally thought,"
he said. "I can see it protecting older people and children
Danaher said he enjoyed putting the knowledge he'd
acquired in other engineering classes to use in the type of
team project he may face in the working world. "The senior
design course was incredible," he said. "It gives you the
kind of hands-on challenge that many other college students
don't get the chance to experience."
The crash protection system was one of nine projects
completed this year by students in the engineering design
course. The class is taught by Andrew F. Conn, a Johns
Hopkins graduate with more than 30 years of experience in
public and private research and development. Each team of
three or four students, working within budgets of up to
$10,000, had to design a device, purchase or fabricate the
parts and assemble the final product. Corporations,
government agencies and nonprofit groups provided the
assignments and funding. The course is traditionally a
well-received, hands-on engineering experience for Johns
To view an online video about this project, go to