February 25, 2003 - Brain Injury Association of America, www.biausa.org, (703) 761-0750
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“Amusement Parks are limited experiences whose attraction lies in the immediate physical gratification of the thrill ride- the exhilaration of speed, the push and pull of gravity, the rush of adrenalin and the illusion of potential bodily harm.”
In the Fall of 2001, U.S. Representatives Edward Markey (D-MA) and Bill Pascrell, Jr. (D-NJ), along with 12 additional Members of Congress requested that the Brain Injury Association of America review the most current information on the safety of amusement park rides, mainly roller coasters, as there were concerns by constituents on their safety vis-à-vis acquired neurological traumas. A panel was assembled consisting of scientists in the fields of biomechanical engineering, epidemiology, clinical medicine, basic neuroscience, and neurotraumatology as well as a representative of the amusement park industry who had extensive experience in the design and operation of roller coasters. Beginning in July 2002, a series of biweekly telephone conferences were held to evaluate and review the existing scientific and industry data in this area and to critically analyze the scientific merit of these. This activity culminated in a meeting convened over a three-day period in Alexandria, Virginia in November 2002 to finalize the conclusions and develop a series of recommendations based upon a dispassionate, objective review of all relevant materials.
The human body is a wonderfully sophisticated biomechanical system with:
Amusement rides utilize these biomechanical systems and equally important “the human perception” to entertain and thrill. Ride designers pay particular attention to perception and create an illusion of danger. People ride roller coasters not only for the visceral effects, but also for the perceived “death defying thrills”.
The kinematics of a loaded roller coaster moving along a path we know a priori can best be described in terms of path variables. The instantaneous acceleration vector of the center of gravity of the vehicle, at any point in time, consists of two components: one component in a direction tangent to the path and a second component (in the osculating plane) at right angles to the path and pointing toward its center of curvature. The tangential component is the rate of change of the tangential velocity while the normal component is the square of the speed divided by the radius of curvature as given in Shames (1996). As the roller coaster moves along its prescribed path, it is very important to note that an acceleration vector is always present and its components change continuously as a function of time. Thus, by virtue of Newton’s second law of motion, forces will always be acting on the roller coaster as well as on its occupants.
A potential association between ground acceleration of a vehicle and occupant head injury has been recognized for a long time. The acceleration pulse required to cause physiological dysfunction of the brain of primates has been known since the late 1970’s and early 1980’s. The paper by Domer et al. (1979) showed an acute change in the function of the blood-brain barrier of rhesus monkeys subsequent to whiplash trauma. Similarly traumatized rhesus monkeys were shown by Liu et al. (1984) to result in subcortical electroencephalogographic (EEG) changes in the limbic system of the brain. The linear and angular accelerations producing these physiological dysfunctions can be theoretically scaled from the rhesus brain to the human brain. Because the rhesus brain is smaller than the human one, the human brain can withstand a lesser acceleration pulse. The only in vivo human dysfunctional data is from studies of human volunteers exposed to whole body accelerations in a centrifuge, Whinnery & Whinnery (1990). Data from these studies were used to set limits for accelerations that are applied to humans over several seconds in duration.
Having the acceleration of the center of gravity of the loaded roller coaster, we must now describe its motion about the center of gravity. Without belaboring its mathematical complexities, we can simply state that the motion about the center of gravity can be described by three angles: roll, pitch and yaw. Stated non-rigorously, the moment of the forces acting on the roller coaster is proportional to its angular acceleration. The proportionality constant is the mass moment of inertia matrix of the loaded roller coaster.
Given the general nature of amusement rides it is clear that a human rider does not exactly follow the motion of the vehicle. The human body represents a “viscoelastic mass” and dampens many of the higher frequency accelerations. Generally, acceleration measurements made on the riders are less that those made on the ride with some exceptions, e.g., the body’s unique muscular system reacts to sustained forces and can sometimes increase or amplify certain motions. If a roller coaster is in a left turn and the passengers have fully responded to this turn, i.e., their neck muscles are holding their head up straight resisting the lateral force, if the roller coaster suddenly enters a right turn and the muscles may still be trained in the opposite direction and may actually accelerate the head instead of righting it. This phenomenon is sometimes referred to as “neuromuscular addition” and ride designers strive to minimize it to minimize the potential for neck strains.
Therefore, neuropsychologists and biomechanical engineers, who understand the response of the conscious human body to various types of motion, must analyze the resulting accelerometer test data. These specialists analyze the accelerometer data understanding that the human body is a viscoelastic mass and that certain short duration impact accelerations are absorbed or reduced by this viscoelastic mass while others are not.
|Measurement of Acceleration on Amusement Park Rides
Typically, a 3-axes accelerometer is used to measure the acceleration on amusement rides. Accelerometer measurements are made during a normal operating cycle with accelerometer placement and vehicle loading in accordance with the American Society for Testing and Materials standard, ASTM F 2137-01, “Measuring the Dynamic Characteristics of Amusement Rides and Devices.” This standard includes:
A separate ASTM standard, Z9591Z “Standard Practice for the Design of Amusement Rides and Device,” establishes acceleration limits for amusement rides. (This standard is discussed later herein and in the Relevant Standards section of this report.)
Crash Test Dummies
Vibrations, which are accelerations that oscillate rapidly relative to the overall motion, also are modified by the body and may be partially absorbed. The body’s tactile sensors may detect these “high frequency” vibrations, but overall motion of the body due to them is minimal. Most people have experienced high frequency vibrations that do not appreciably alter the overall motion. Examples include an out of balance tire on an automobile or that pesky caster on the shopping cart.
Vibrations that persist for long periods of time can be bothersome to humans, not from the standpoint of injury, but rather from fatigue. The body of knowledge for this type of “whole body vibration” and the resulting “fatigue reduced proficiency” is covered in the International Standard, ISO 2631. Its primary use is for long-term exposure to various occupational vibrations (heavy equipment operators, truck drivers). Amusement ride cycles are rarely long enough for vibration-induced fatigue to be a factor.
Test engineers may employ filters to remove extraneous vibration and noise from the test data in order to see more of the overall movement of the amusement ride. This is normally done electronically on the digitally stored data, but also can be done directly on the accelerometer signal. The disadvantage of the latter being that some frequency related analysis may not be possible after the filtered data is stored. For this reason, the standard filtering method is electronic and ranges from 5 Hz to 100 Hz depending on the specific analysis being made. For purposes of evaluating amusement rides relative to a standard acceleration limit, ASTM standard Z9591Z specifies 5 Hz, but different types of analyses are routinely made at other filter rates.
|Amusement Ride Acceleration Limits
ASTM Z9591Z “Standard Practice for the Design of Amusement Rides and Devices,” establishes design acceleration limits for roller coasters and most other amusement rides. The ASTM technical committee that developed these limits included the expertise of:
This standard also drew from the important criteria, information and findings of other standards such as the “Central European Norm,” which was developed over the last 10 years by the European Union.
(See Appendix A for a complete version of the ASTM acceleration limits.)
|Everyday Life Accelerations
Several researchers have examined the head acceleration values resulting from everyday activities. While the results of such studies have yielded some surprisingly high numbers, it is important to note that maximum or average acceleration alone is a poor index of the injury potential of a particular activity. For example, simply striking oneself in the head with the heel of the hand can produce as much as 10 g’s of maximum acceleration for a short time, but has little injury potential. Conversely, occupants in experimental rear impact motor vehicle collisions report minor symptoms of neck strain with head acceleration of only 2-3 g’s (Siegmund et al. 1997).
There are several reasons for this disparity: the duration of the acceleration must be taken into account (the hand strike example produces only a few milliseconds of acceleration pulse, whereas the experimental crashes produce approximately 100 milliseconds of peak acceleration). Additionally, the differential acceleration produced by the activity must be considered. In other words, activities in which the entire body is accelerated as one unit will not produce injury at the same rate as other activities that result in a difference between torso and head acceleration. For example, a sneeze has been reported by Allen et al. (1994) to produce as much as 2.9 g’s of peak head acceleration. The head acceleration results solely from the muscular contraction of the sneezer and has relatively minimal injury potential because the braced sneezer is prepared for the sudden head movement. In contrast, the unprepared occupant in a rear impact motor vehicle collision has a higher injury potential because he or she is not causing or bracing for the acceleration, and the impact with the seatback results in a difference in acceleration between the head and torso. The same principles are applicable to the evaluation of roller coaster rides. Peak head acceleration may yield less useful information than knowing the duration, direction(s) and both the linear and angular components of this head acceleration.
|Relevant Standards Governing Amusement Rides
The nationally recognized standards for amusement rides are the American Society for Testing and Materials (ASTM) standards. ASTM was organized in 1898 and provides a management/administrative system for the development of voluntary, consensus standards. The technical committee on amusement rides safety standards (ASTM F-24) was established in 1978 and is presently made up of almost 400 individuals including manufacturers (20%), operators (35%) and general interest (45%). This committee develops new standards on an ongoing and as needed basis. Existing standards also are reviewed and updated every two years. As with most standards in the United States, ASTM standards become mandatory when cited in a contractual agreement or when referenced and mandated by a governmental body.
The ASTM standards for amusement rides actually consist of 14 separate standards covering issues such as design, operations, maintenance, quality control and testing. States typically adopt the ASTM standards making them law in that state and as more states adopt the same standards, they become the national standard. (See sections on State Regulations and Local Standards and Regulations.)
Acceleration limits for amusement rides are included in the ASTM standard Z9591Z “Standard Practice for the Design of Amusement Rides and Devices.” (The specific section of this standard that outlines acceleration limits is given in the Appendix A.)
The establishment of acceleration limits in amusement ride standards is relatively new (Europe first published acceleration limits in 1997), but designers and engineers have designed rides with purposely-limited accelerations for many years. The body of technical information available to designers and engineers includes general engineering principles, physical laws and commonly accepted acceleration limits. These acceleration limits, which are also the basis of the ASTM standard, are the outgrowth of 50 years of governmental research, university research, aerospace medicine and the work of other standards organizations around the world.
Roller coaster designers and engineers have backgrounds and training in various engineering disciplines. They are typically registered professional engineers with mechanical, civil, electrical and biodynamic engineering experience.
Because roller coasters are complex machines with exacting mechanical/structural requirements, they are designed using commonly accepted engineering practices and standards, the same standards that are used for designing aircraft, automobiles, bridges, skyscrapers, etc. Some of the standards that are referenced and required by the ASTM Z9591Z ‘Standard Practice for the Design of Amusement Rides and Devices” are detailed in Appendix B.
Most states that have amusement rides operating within their jurisdiction have enacted legislation that regulates their use. The ASTM standards are often adopted by the state and therefore become law in that state. According to the CPSC, approximately 42 states, which includes almost all states with fixed site amusement rides, have amusement ride regulations. Compliance in these states is typically monitored through the use of state ride inspectors and/or insurance inspectors.
Local Standards and Regulations
A fixed-site amusement ride must comply with local building codes before it can be constructed or operated. These codes include Building Officials Code Administrators International (BOCA), Uniform Building Code (UBC), Southern Building Code Congress International (SBCCI), National Fire Protection Association (NFPA) Life Safety Code, National Electrical Code (NEC) and others. The codes cover structural, mechanical, electrical and general occupancy/use standards and requirements. Compliance is monitored and checked by building and safety officials having jurisdiction.
Industry Self Policing
The U.S. amusement industry is more than a century old. It is an industry in which safety is not only a moral obligation, but also a prerequisite to doing business for without a safe environment, the industry would not exist. It is for these reasons that the industry has developed extensive and sophisticated systems of checks to insure the safety of their facilities. Amusement rides are designed, built, maintained and operated to exacting requirements. The common philosophy that runs through the industry is that “an amusement ride must be designed, constructed, installed, maintained and operated properly in order to consistently attract visitors;” thus, redundant and fail-safe designs are the norm for amusement rides.
The following steps are of paramount importance because they are recognized as crucial elements to the survival of the industry:
Several industry groups conduct extensive technical training and continuing education programs for park operating personnel. For example:
Amusement Park Attendance
The United States Consumer Products Safety Commission (CPSC) tracks amusement park injuries that require medical attention at a hospital. This data indicates that the total of all injuries from all causes is approximately 6,500/year and the overwhelming majority of these are treated and released. Only about 130 people per year require an overnight stay. Therefore, the likelihood of being injured on a ride seriously enough to require hospitalization is about 1 in 25 Million.
Highlights of the CPSC 2002 Report along with injury rates are as follows:
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Injuries tracked by the CPSC are segmented into seven categories. The categories and their averages for 1997-2001 (shown above) is:
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Percent of total may not sum to100 percent due to rounding.
Reported injuries include non-ride related injuries.
Assuming that all of the reported injuries in the trunk/neck/head/face/ear/pubic area occur on an amusement ride, which they do not, the percentage of injuries is still extremely low, i.e., »0.0000007% of rides result in an injury in these areas.
|Commitment To Safety
It is clear that the amusement industry has an impressive safety record and that the industry strives constantly to strengthen its training, maintenance and testing programs. In addition, the industry abides by numerous state and local licensing and inspection regulations, adopts the latest technologies and techniques, and submits itself to regular rigorous insurance examinations. This commitment to safety has allowed the amusement industry to thrive for more than a century, and will ensure that it continues to provide safe, quality, family entertainment for many years to come.
AIMS International. 1250 SE Port St. Lucie Blvd, Suite C, Port St. Lucie, FL 34952.
Allen, M.E., Weir-Jones, L., Motiuk, D.R., Flewin, K.R., Goring, R.D., Kobetich, R., Broadhurst, A. (1994). Acceleration perturbations of daily living. Spine, Vol. 19, Number 11, 1285-1290.
Amusement Business. (2001). 49 Music Square W.,Nashville, TN. 37203-3213.
ASTM International. F-24 Standards for Amusement Rides and Devices. West Conshohocken, PA. 19428-2959.
Cartmeil, R. (1974). The Ultimate Roller Coaster: The New York Times Company.
Disney Linkage. Retrieved December 4, 2002, from www.scottware.com.au/theme/.
Domer, F.R., Liu, Y. King, Chandran, K.B. & Krieger, K.W. (1979). Effect of hyperflexion-hyperextension (whiplash) on the function of the blood-brain barrier of rhesus monkeys. Experimental Neurology, 63, 304-310.
Economic Research Corporation. 10990 Wilshire Boulevard, Suite 1500, Los Angeles, CA 90024.
European Committee for Standardization. prEN13814, Central Secretary ure de Stassart 36, B-1050 Brussels, Belgium.
Harrison Price Company. 2141 Paseo Del Mar, San Pedro, CA 90732.
International Association of Amusement Parks and Attractions. 1448 Duke St., Alexandria, VA 22314.
Liu, Y. King, Chandran, K.B., Heath, R.G.& Unterharnscheidt, F. (1984). Subcortical EEG changes in rhesus monkeys following experimental hyperflexion-hyperextentension (whiplash). Spine, 9, 329-338.
Onosko, T. (1978). Funland USA: Ballantine Books.
Pescovita, D. Roller Coasters: Inventing the Scream Machine. Retrieved December 6, 2002 from www.britannica.com.
Shames, I. H. (1996). Dynamics (4th ed.), Prentice Hall, Englewood Cliffs, New Jersey.
Siegmund, G.P., King, D.J., Lawrence, J.M., Wheeler, J.B., Brault, J.R., Smith, T.A. (1997). Head/neck kinematic response of human subjects in low-speed rear-end collisions. Proceedings of the 1997 Stapp Car Crash Conference. SAE paper # 973341. 357-385.
Silverstein, M. (1986). Scream Machines, Roller Coasters Past, Present and Future: Walker & Company.
U.S. Consumer Products Safety Commission. (2002). Amusement Ride Related Injuries and Deaths in the United States. Directorate for Epidemiology, Division of Hazard Analysis. 4330 East West Highway, Bethesda, MD 20814.
U.S. Consumer Products Safety Commission. Directory of State Amusement Ride Safety Officials, Office of Compliance, Division of Recalls and Compliance. Washington, DC 20207.
Varney, N.R., Varney, R.N. (1995). Brain injury without head injury: some physics of automobile collisions with particular reference to brain injuries occurring without physical head trauma. Applied Neuropsychology. 2. 47-62.
Whinnery J.E. Whinnery A.M. (1990). Acceleration-induced loss of consciousness. A review of 500 episodes. Archives of Neurology. 47(7):764-76.
|Tables & Appendices
Table 1: Basic use statistics for amusement parks in the United States
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Using information from all sources, the International Association of Amusement Parks and Attractions lists 2001 attendance as 319 Million. Other pertinent data can be summarized as follows:
Appendix A: Acceleration Limits
(Section-7 of ASTM Z9591Z “Standard Practice/Guide for the Design of Amusement Rides and Devices”)
7.1.1 Amusement rides and devices shall be designed such that the accelerations, as measured in accordance with ASTM F-2137, are within the limits specified in this practice.
7.1.2 Amusement rides and devices or major modifications that are designed to operate outside the acceleration limits herein shall include justification in the Ride Analysis. The justification shall include a review by a biodynamic expert.
7.1.3 Acceleration can vary greatly depending on the type and design of the amusement ride or device and the effect of these accelerations are dependent on many factors that may be considered in the design (see Appendix). Accelerations shall be coordinated with the intended physical orientation of the patron during the operating cycle. Rides and devices with patron containment systems shall be designed such that the patron is suitably contained and positioned to accept these accelerations. The Patron Restraint and Containment analysis shall consider cases related to patron position within the restraint as determined by the Designer/Engineer. Figure 4 illustrates the coordinate system utilized.
7.1.4 Sustained Acceleration Limits are shown in Figures 5, 6, 7, 8, and 9. The following definitions apply:
The Patron Restraint and Containment Analysis shall be used to determine the type of restraint. The type and performance of the restraint system selected may require a reduction in the acceleration limit.
Figure 10 Reversals in X and Y (5 Hz Filtered Data)
Appendix B: Additional standards references and required by ASTM Z9591Z
"Standard Practice for the Design of Amusement Rides and Devices"
Appendix C: Roller Coaster Evolution
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