The Biomechanics of Pediatric Injury

Saferparks recently submitted a proposal to the ASTM F-24 committee suggesting changes to the design standard for rides and devices (F2291).  The changes are intended to reduce the risk of containment failures involving young children in new rides by requiring a child safety analysis as part of the ride analysis.  Designers would still be allowed to use their own judgment when deciding where to draw the line on acceptable risk, but the manufacturer's documentation delivered with the ride would be required to include a detailed description of "any significant factors that may affect the safety of child patrons which the designer/engineer chose to mitigate by requiring child patrons to protect themselves or by requiring one patron to protect another patron from a potential hazard (e.g., accompanied rider rules for children)".

The proposed changes leave design and innovation in the hands of the engineers, which is necessary and appropriate.  However, it is also necessary and appropriate that parents be made aware of machinery hazards that can cause serious injury to their children.  The proposed changes would start propagating accurate, specific information down the communication chain.  Designer/engineers would be required to consider how the smallest children allowed on board might get into trouble while using the machine, but they would not be required to prevent those hazardous interactions as long as they "sufficiently inform the user about the residual risks in the different phases of the life of the machinery".

Saferparks is proposing a flexible solution intended to keep the thrills and the children intact.

Saferparks' child safety proposal was inspired by a presentation on the biomechanics of pediatric injury at last year's International Consumer Product Health and Safety Organization conference.  The keynote address, given by Dr. Gary A. Smith, Director of the Center for Injury Research and Policy at Children's Hospital in Columbus, Ohio, addressed pediatric injury prevention from a scientific standpoint.  Dr. Smith focuses his research on the physical mechanisms of injury with the aim of preventing or reducing the physical damage to the child.

Injury =	Physical damage due to the transfer of energy (kinetic, thermal, and chemical energy, electricity and radiation) or the absence of essentials, such as oxygen and heat.  Exposure may be acute or chronic.

Note the similarities between Dr. Smith's approach to pediatric injury prevention and the amusement ride industry's approach to preventing acceleration-related injury.  Imagine how much progress we could make toward reducing ride-related injuries to children if all the stakeholders were willing to spend even a little bit of their time jointly exploring the child safety problem from Dr. Smith's perspective.  Children under age 13 account for half of all ride-related injuries.  And some of those injuries involve the transfer of enough energy to crush a limb or a life or the collective heart of a family.

Amusement ride accident victims quite often speak about the transfer of energy.  They may not language it exactly that way, but the moment of energy transfer dominates their recollections.  My son was five years old and weighed only 40 pounds when he was hurt (less than 1/4 of the weight assigned to patrons for design purposes on a family ride).  When I asked him what had happened, David said that a "big hot wind" had taken his foot.  My husband and I assumed he was inventing a childish fantasy to explain the unexplainable.  Several years later, when David had a larger vocabulary, I asked him again what happened the night he was hurt.  This time he told me he remembered intense heat.  The "big hot wind" story wasn't a fantasy.  It was a preschooler's way of describing the transfer of enough thermal energy (caused by friction and pressure) to tear his own foot in half.  Thankfully, the human brain has no long-term memory for pain itself.  David, now a well-adjusted 6th grader who surfs, snowboards, and plays far too much baseball, remembers nothing more than warmth on his foot and a park employee who tried to distract him with a stuffed animal.

In the seven years since David's accident, the industry and I have had every conversation it is possible to have about our litigious society, disobedient children, irresponsible parents, and the statistical insignificance of amusement ride accidents.  I am steadfastly working toward the day when the industry and I can have a compassionate conversation about the crushed children, one that draws on the industry's problem-solving strengths rather than its moral judgments.

Dr. Smith has found a way of stripping off the stories that people (on all sides) inevitably spin around events that are too painful to bear.  He limits his study to the facts directly surrounding the energy transfer -- in this case that would include the containment system, seating configuration, age and size of the child, hazard exposure, ride operator's ability to see the riders, and reaction/stopping time (i.e., can the child get into a dangerous position in less time than it takes an alert operator to stop the ride?).  Saferparks is developing a teaching tool to help parents recognize these types of risk factors when they're choosing rides for their children.

Dr. Smith's biomechanical view of childhood injury simplifies assessment of prevention strategies as well.  An effective intervention is one that prevents or reduces the transfer of energy to the child.  Sometimes a minor change can be quite effective, say adding a few inches to the foot well of an open-sided ride used by short-legged preschoolers.  Good engineers will formulate effective solutions if they're allowed to learn from the unlucky folks who experienced the failure firsthand.  Without that firsthand knowledge, even the best engineers are left guessing.  I am handicapped in the opposite way.  I know how children of various ages might get into trouble on amusement rides, but I don't know as much as I need to about how specific rides are designed.  In an ideal world, the industry and I would combine our knowledge and talents for the benefit of the children.

I hope the F-24 committee will give serious consideration to Saferparks' proposal.  In the meantime, I steadfastly work toward the day when the industry, by consensus, commits itself to finding effective interventions that prevent or reduce the transfer of damaging energy to their smallest customers.

Reference: ISO/IEC 14121 - "Safety of machinery - Principles of risk assessment"