ASTM F1292-09 Standard Specification for Impact Attenuation of Surfacing Materials Within the Use Zone of Playground Equipment. Recommended Ballot Items(s): Item 1, Section 8.3.3, Accelerometer Calibration Standard Currently Reads: Accelerometers shall be calibrated by reference to a National Institute of Standards and Technology (NIST) traceable standard using a shaker table to excite a range of frequencies and amplitudes determined suitable by the accelerometer manufacturer. The calibration procedure shall include, as a minimum, the range of frequencies from 2-2000Hz. Suggested change: Accelerometers shall be calibrated by reference to a National Institute of Standards and Technology (NIST) traceable standard using a shaker table to excite a range of frequencies and amplitudes determined suitable by the accelerometer manufacturer. The calibration procedure shall include, as a minimum, the range of frequencies from 20Hz-2KHz. Commentary and rational David Splane: I have found through numerous calibration house/manufacturer/vendor requests for Low Frequency calibration, (2-2000Hz), that this service is simply Not offered, or available. Evidently, calibration within this range requires use of long stroke shaker, generating controlled vibration, which is limited. Additionally, manufacturers whom may be able to provide this service, in general, cannot provide proof or reference to a National Institute of Standards and Technology (NIST) traceable standard(s). It is also noted that calibration services, within this range, incur additional cost(s) and lead time(s). Commentary and rational Paul Bamburak, Alpha Automation,Inc: I think there is enough technical basis to argue that the 20Hz lower calibration frequency is sufficient, and that we rely on the time constant to predict the low frequency response. I reviewed the original certificates for your systems. One has TCs of almost 3.0 Seconds (better than required) while the other has TCs slight shorter than 2.0 seconds. My anecdotal experience after building almost 300 systems is that there is no difference over the range of TCs from the original shorter ones we made (0.5 seconds) to the longer ones (3.0 seconds.) I believe that there are so many other things happening during the impact that any possible shortcomings in the instruments are swamped by the variability of the surfaces. My practical experience also shows that the longer time constants are harder to manufacture and produce more variable results sensor to sensor. Our sensor is custom made by Dytran, and it is the only one we have tested than can successfully work on pea gravel (some people still use this) and similar surfaces. Our purchase spec is for a TC = 2.0 seconds but they come in anywhere from 1.8 to about 3.0. You cant just tweak it to get a higher TC you have to discard the internal sensor elements and start over. A very expensive proposition. I think that when a specifications drafted practical concerns such as these also need to be considered. Item 2, Section 9.4, Determination of Missile angle Standard Currently Reads: In a free-fall impact test, the angel of the missile at the onset of impact and at the instant of maximum acceleration shall be calculated. For the purposes of this calculation, the onset of impact shall be the data sample at which the resultant acceleration first meets or exceeds a threshold value of 5g . The angle shall be calculated from the component accelerations. The cosine of the missile angle shall be calculated as: Section 11.3.3. Data Check Standard Currently Reads: If a free-fall impact test is used, calculate the missile angle at the onset of impact at the instant of maximum resultant acceleration, in accordance with 9.4. If the calculated missile angle at either point exceeds 10 (that is, the cosine of the missile angle is less than 0.966), data from the trial shall be discarded. Suggested change: When performing a free-fall impact test, with use of a triaxial accelerometer, calculate the missile angle at the onset of impact at the instant of maximum resultant acceleration, in accordance with 9.4. If the calculated missile angle at either point exceeds 20 , data from the trial shall be discarded. Commentary: Testing for more than 12 years at heights in excess of 12 demonstrates that many drops result in valid and consistent data; however the angle exceeds the 10o and either invalidates the drop or requires additional testing. This need to meet the 10o angle is further exacerbated with the need for a portion of the protective surface to meet the requirements of the ADA, which allows this surface to have as much as a 6.25% slope making the achievement of the angle even more difficult. Since the angle or 10o has not been demonstrated to be a problem this change would facilitate testing and the protection of children.
Keywordscritical fall height; head impact; head injury criterion; HIC; impact; impact attenuation; impact test; injury; play; playground; play structure; shock; surface; Impact testing--sports applications/equipment; Instrumental measurement; Playground equipment--specifications; Sports equipment--specifications; Sports facilities playing surfaces--specifications; Velocity; Attenuation; Comparison techniques; Consumer safety specifications (playgrounds); Digitizers; Free fall test method; Head form velocity;
Draft Under Development