Rationale

Limits currently contained in Section 7 of ASTM F2291 do not address accelerations with a duration of less than 200 msec as explicitly stated in 7.1.4.2. These events are commonly referred to as “impact events.”

While sustained accelerations (> =200 msec) limits are generally driven by cardiovascular response, impact event limits are driven by neuro-muscular responses. Biodynamic considerations for impact events are typically associated with the interaction of the patron and the patron containment system. A primary metric of this interaction involves the velocity of any potential contact between the patron and the patron containment system, which in turn is a function of the change in velocity undergone by the ride vehicle over short periods of time (i.e. less than 200 msec). Change in velocity is established in the aeronautical, automotive, and biodynamic literature as an important metric for impact events.

A method of consideration of the biodynamic effect of impact events is contained within Appendix X.11 including a calculation method for Delta-V (change in velocity undergone by the ride vehicle over durations of 200 msec or less) and Average Acceleration (Delta-V divided by the duration of the event).

To establish informed safe limits of Average Acceleration, data was collected, per F2137, and analyzed, per method in Appendix X.11, from rides from manufacturers and owners across the industry with and without known injuries related to impact events. Details about ride type, class of restraint, and whether a headrest was present was collected for each of these rides. More information was not collected to best ensure confidentiality and discretion. In total, 142 rides were reviewed including wood coasters, steel coasters, family rides, bumper cars, and flat rides.

Upon compilation and review, no clear pattern in which data from injurious rides stood out in Delta-V vs. duration or Average Acceleration vs. duration, regardless of restraint class or whether there was a headrest present. However, injuries have been known to occur due to this phenomenon. Because biodynamic considerations for impact events are typically associated with the interaction of the patron and the patron containment system, it is hypothesized that correlation would be more evident between injurious and non-injurious rides if the analysis could consider the additional dimension of specifics regarding the potential impact areas between patron and patron containment device. This would, in theory, indicate that rides above a certain Average Acceleration threshold that are not injurious must have a patron containment system that properly accounts for and mitigates this potential injurious characteristic due to impact events. This analysis is not possible given the method of confidentially collecting and analyzing the 142 rides. However, it can be deduced that an explicit requirement to consider the patron containment system in this context above a certain potentially injurious value of Average Acceleration or Delta-V will yield a higher threshold of safety within the industry.

To determine a known safe limit of Delta-V, one may consider walking into a wall at an average human walking speed (~5ft/s). Above this speed, the patron containment system, specifically what may be impacted, shall be considered. The designer/engineer shall determine the appropriate design of the patron containment system including whether it is an addition of padding (reducing the potential travel distance of the patron during an impact event and/or absorbing energy upon impact) or removal (eliminating the object that the patron may impact during an impact event) that is most appropriate for the given system.

Regarding inclusion of a limit for Delta-V rather than Average Acceleration, the Acceleration Task Group had much discussion. Ultimately, it is simpler and more explicit to represent the Delta-V limit, a constant, within our specification. This can easily be converted to Average Acceleration (5 ft/s divided by the duration of event) during the designer/engineer’s analysis if desired.

While the data from 142 rides yielded a valuable study, it is small percentage of existing rides. Please reach out for any information regarding checking data including any concerns that this proposed change would suggest any non-injurious rides are non-compliant.