ASTM G-Force Presentations 2001

Notes from G-Force Presentations made to ASTM F-24 committee
February 2-4, 2001  Tampa, Florida

Proposed New Jersey Regulations
Russian Standard
European Standard
Needed:  A Better Injury Reporting System
Needed:  Information on Children's Tolerance for High-G Rides

As part of its work on a major expansion of the design and manufacture standard, the World Standards task group heard presentations on g-force standards from the New Jersey Department of Community Affairs, the Russian Association of Amusement Parks and Attractions (RAAPA), and two European ride manufacturers. 

Proposed New Jersey Regulations

In response to a double coaster fatality in 1999 caused by faulty design and substandard parts, the New Jersey state legislature passed a law granting regulators the right to approve the design of new rides brought into the state.  Formal rule-making on the specifics of the new regulations will begin in April.  State regulators presented their proposal to the industry during last week's meeting of the ASTM F24 committee.

The most controversial aspect of New Jersey's plan is the section on g-force limits.  The state is proposing that a two-tiered certification system be used to analyze the effects of g-force.  In the simplest case, the forces created by a new ride must fall within limits specified in New Jersey's g-force table.  Those criteria address several factors, including magnitude, direction, and duration of force.  New rides that exceed those limits are not automatically rejected, but will be subject to a more extensive review.  In essence, the state wants to know how the manufacturer plans to mitigate the effects of g-forces that exceed those in the limit table.  For instance, a change in the design of the seat angle, padding, or restraint can reduce the adverse effect those forces will have on the human body.  There are no absolute upper limits set on g-force in the proposed New Jersey regulations, but manufacturers who push the envelope must convince the state that the design, as a whole, leaves a reasonable margin of safety.

New Jersey's proposed g-force limits are based on data from military aviation testing, automobile crash tests, and g-force studies from other countries (Russia, Germany, Australia).  State regulators obtained dynamic force profiles for 150 U.S. coasters from an industry consultant named Pruitt.  That data is highly confidential, and could not be shared with the ASTM members present, although several members said they were were familiar with Pruitt's measurements.  New Jersey asked the industry for injury data on the 150 coasters sampled, so that they could look for correlations between various g-force parameters and injury rates.  The industry declined to provide injury data. 

Russian Standard

The Russian standard is based on military aviation tests on physically healthy adults, and centrifuge and vascular strength tests on adults of various ages.  Russia's testing produced the following results:

• 96 subjects ranging in age from 21-50 were exposed to 5g head-to-pelvis acceleration (4gs plus normal earth's gravity). Under those conditions:  
  • None of the subjects between 26 and 45 years of age lost consciousness. 
  • 18% of the subjects aged 21-25 years lost consciousness.
  • 20% of the subjects aged 46-50 years lost consciousness. 
• Repeated rides on high-g rides can lead to loss of consciousness.  Amusement park patrons should be warned to rest 20-30 minutes between rides.
• Ability to tolerate high accelerations declines as adults age and blood vessels in the brain lose strength.  Older patrons and patrons who suffer from hardening of the arteries should avoid high-g rides.
• The Russian standard sets a 5g limit on head-to-pelvis accelerations lasting longer than half a second (4gs induced by the ride plus 1g of normal earth's gravity). 

European Standard

Like New Jersey's proposal, the CEN standards developed for European rides specify g-force limits, but allow rides to exceed those limits as long as the effects of g-force are accounted for in the design of the passenger containment system. 

The CEN standards were based primarily on the 10-year Dusseldorf Study commissioned by the German government  following a series of coaster-related injuries, and conducted through collaboration between industry and the medical community.  Acceleration profiles for 250 gravity coasters were sampled at adult neck level (60 cm above seat).  Anatomical dummies modeling the human musculoskeletal system were exposed to accelerations in the z-direction (head-to-pelvis) and y-direction (lateral or side-to-side), to see how far the neck would bend under force.  G-force limits were chosen so that patrons' necks would not bend further than the allowable angle for the study (one manufacturer said he thought the acceptance criteria was 37 degrees).  After a set of g-force limits had been determined, the group studied injury data for all coasters that fell within those limits.  The injury data validated the chosen limits by showing an acceptably low rate of g-force related neck injuries for rides that met the limiting criteria. 

Known limitations of the Dusseldorf study and the CEN standard:

• The CEN standard sets limits for acceleration in the z- and y-directions only (head-to-pelvis and lateral).  It does not set set limits on acceleration in the x-direction (front-to-back), nor does it address jerk.
• The rides in the sample set were all traditional gravity coasters; no data was collected on launched coasters.
• The test measurement methodology used by the Europeans is different than the test measurement methodology for dynamic force recently approved by the ASTM F24 committee.  Because the Dusseldorf study was commissioned to investigate neck injuries, the accelerometer data was taken at adult neck level.  In recent years, measurements taken at the rider's center of gravity (heartline) have become the industry standard.  Although the concepts are the same regardless of where the measurements are taken, the numbers obtained through different methodologies cannot be compared or contrasted.
• The CEN standard is limited to seated passengers.  The limits are not necessarily valid for rides in which patrons stand or lie prone.
• The Dusseldorf Study was designed to investigate neck injuries.  The limits chosen may not be adequate in preventing other neurological injuries associated with high-g rides.

Needed: A Better Injury Reporting System

The half-day discussion on safety issues related to dynamic force highlighted the need for a better accident reporting system, in order to compare dynamic force parameters with injury statistics.  New Jersey regulators studied the dynamic force profiles of 150 U.S. coasters, yet were unable to obtain injury records from the industry for those same coasters.  The lack of available safety data on U.S. rides made it more difficult for New Jersey's  engineers to determine safe parameters for dynamic force.  They had to rely on safety data from other industries, such as military aviation and automobile crash testing, and ride-related data from Russia, Australia, and Europe. 

Needed:  Information on Children's Tolerance for High-G Rides

One of the critical concerns raised at the ASTM meeting was the lack of data describing the effects of g-force on children.  The Russian standard was derived from military aviation testing on healthy adult males, and centrifuge testing on 96 adults of various ages.  The European standard was derived from testing on adult-sized anatomical dummies.  The New Jersey proposal is based on military aviation testing, automobile crash test data, and findings from other countries (i.e., Russia, Germany, Australia).

Parents should realize that children may be more vulnerable to the effects of g-force than adults.  The Italian representative told the ASTM F24 committee that children under age 12-14 should avoid certain rides, but they don't know which rides pose a danger.