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testing the impact attenuation of loose-fill playground surfaces

by:KK INFLATABLE      2020-06-18
Target-
Our goal is to measure the impact attenuation performance of five loose materials
Fill the surface of the playground at various drop heights, material depths and conditions. Methods—
In a laboratory environment, a form of a skull is dropped on loose objects of different depths
Fill the material in a height increment of 1 feet until it exceeds the critical deceleration value.
The effects of Test box size, material temperature and compression were also studied. Results—
The data show that the larger test box size will affect the test results.
Uncompressed materials perform quite unexpectedly, that is to say, the toughness does not necessarily increase as the depth of the material increases, and the temperature does not have a uniform effect.
Compression before testing improves the consistency of the results. Conclusion—
Current standard testing procedures (ASTM F1292)
Seems a problem for loosefill materials.
Our results show (1)
Rubber debris is the best performance; (2)
There is no difference between sand, wood fiber and wood chips; and (3)
The pea gravel performed the worst, making it a bad choice for the playground to be laid.
Material Selection
Fill materials commonly used in the playground were selected: sand, pea gravel, wood chips, engineered wood fibers and crushed rubber.
We use ASTM standards for material selection as much as possible.
8 ASTM C897 gypsum sand 9 was selected because of its availability and because its thickness is between fine sand and coarse sand as described in the CPSC manual.
Consumers find it difficult to follow the CPSC guidelines because there is no standard definition of pea gravel.
6 Therefore, since larger particles may cause more serious damage if thrown by children, it is recommended to use aggregates not greater than 3/8 on the playground.
ASTM C33 concrete aggregates10 is the only ASTM gravel specification that meets this requirement.
Unfortunately, the total amount that meets the ASTM C33 standard is not readily available throughout the United States;
However, a uniform 3/8 gravel can always be obtained.
Therefore, round gravel particles with a maximum or nominal size of not more than 3/8 are selected as sample materials, which are washed without dust, clay, dirt or foreign matter.
ASTM also does not provide the standard for wood chips;
Therefore, the sample specification follows the CPSC manual description 7-
That is to say, it consists of wood chips, branches and leaves of random sizes collected from wood chippers fed to branches, branches and brushes.
Samples were chopped at least two weeks before the test date.
The ASTM standard does not apply to engineering wood fibers, so this manufactured product consists of engineering wood fibers of random sizes from recognized hard wood, as described in the CPSC manual.
There is no ASTM standard for crushing rubber;
The sample consists of 10 mesh waste rubber particles from recycled materials.
All impact attenuation tests for test equipment are carried out by the Detroit test laboratory, an independent laboratory accredited by the American Association of laboratory certification, in compliance with the requirements of the International Standards Organization/International electrician committee guidelines 25.
The test equipment includes :(a)
12 feet impact tower of Detroit Test Laboratory; (b)
Program C, test method F355 Kia metal head type; (c)
KME, HIC computer IV of M/N 300 series; (d)
M/N 353B17 piezoelectric and accelerometer; (e)
Load cell GSE, M/N 5353-2K; and (f)
Daytronic, strain indicator, M/N 3170.
Equipment was calibrated according to the National Institute of Standards/Standards Laboratory Z540 National Conference1-1994.
The test procedure test conforms to the specification of ASTM F1292-95 11 and is modified as follows.
The test procedure requires the head shape to hit the material in the center of the box.
After at least four hours of conditioning of the sample before the test (
Reach the desired temperature)
, Two thermocouple are placed in the sample, located at about 2 inch and intermediate depth, respectively, to verify that the proper temperature is maintained throughout the testing process.
If the temperature change exceeds the specified temperature, the test will be aborted and completely repeated.
The initial drop height is 1 feet and is increased every 1 feet until the critical height is reached, that is, the HIC value exceeds 1000 or g-
To a maximum of more than 200 or 12 feet (
Maximum height of impact tower in Detroit Test Lab). HIC and g-
The maximum value is calculated based on the mean of the second and third descent of each height. 11Stage 1—
The effect of the box size test using a box with an internal size of 18 × 18 inch and a box with an internal size of 18 × 36 inch.
The test material is 6 inch of the chopped rubber. Stage 2—
At three temperatures, the depth and temperature effects of five samples were tested at depth of 3, 6, 9 and 12 inch (
30 °, 72 ° and 120 °F). Stage 3—
The compression effect fills the sample box to the desired depth.
A machine that loads the top of the sample to 1 with a plate.
125 per square inch (729 lb).
We chose this load because we felt it represented the compression produced by a child of 95 percentile and 12 years old (
The upper age of public playground equipment design).
The drop height is measured from the compaction depth. ResultsStage 1—
The standard test ambient temperature with a tear damage value of 6 inch for the box sizeHead, with an average of 14% X 36 inch boxes lower than the decree x 18 inch boxes (table 1).
The HIC value dropped from 0% to 25%.
Similarly, the box of 18x36 inch is reduced by an average of 11% g-
The largest compared with 18x18 inch boxes; decreases in g-
Max ranges from 2% to 17%.
The 18x36 inch box is used for all subsequent tests because the box size affects the impact attenuation test results and also because the larger box size is considered to be more representative of the actual playground conditions.
View this table: View the inline View pop-up table 1 average head injury Standard (HIC)and g-
According to the box size and drop height, the maximum value of 6 inch chopped rubber at ambient temperature is 2-
The influence of depth and temperature on uncompressed material the compressed material has particularity and inconsistency.
For sand and gravel, there is a considerable difference between HIC and g-values
Wood chips, wood fibers and chopped rubber are more consistent.
For gravel, the second drop reading at each height is always higher than the first drop (
It is not uncommon to increase 150% to 200%).
However, the third decline is often less than the second.
The first and second drops of sand are also different.
These differences are affected by temperature and depth.
At 30 F and 120 F, the readings for the second and third drops are similar.
However, at 72 degrees Fahrenheit, the difference seems to be related to depth.
For the drop height of more than 2 feet, the depth of 6 inch and 9 inch recorded the third drop, always lower than the second.
Instead, the second value is always lower at 12 inch (
Data available on request).
The critical drop height does not necessarily increase with the increase of material depth, and the temperature has no uniform effect in the material (table 2).
For gravel and sand, the critical height does not continue to increase as expected as the depth increases.
Environmental conditions result in the lowest critical height for all gravel depths.
Extreme temperatures tend to improve the shock attenuation of sand and gravel.
For the sand, it should be noted that an increase in temperature will result in a decrease in the critical height of 6 inch, but not at a depth of 9 inch or 12 inch.
View this table: View the critical height of the inline View pop-up table 2 loose feet
Filling the material, through the compression state, Fahrenheit temperature and material depth, the critical height of the wood sheet increases with the increase of the depth at all three temperatures.
For the depth of 120 and 6 inch, the effectiveness of wood chips decreased slightly at 9 inch degrees F.
However, these differences are not so obvious at 12 inch.
As with wood chips, the critical height of engineering wood fibers increases as the material depth increases.
Again, the 120 °F condition is slightly different, but it is not obvious at 12 inch.
The uncompressed crushed rubber has excellent impact attenuation properties.
The critical height of the depth of 6, 9 and 12 inch is 12 feet, which is not significantly affected by temperature. Data (not shown)
It is shown that the impact attenuation increases with the increase of material depth-
For example, for the drop height of 12 feet under ambient conditions, the depth value of 6 inch is HIC = 917 and g-
HIC = 12 inch and G-190 values
Wood Fiber: 738,119;
Wood chips: 754,119;
Sand: 788,192; HIC and g-
Max, respectively.
Discussing our results shows that it is currently used to test loose-
The filling material on the surface of the playground may produce unreliable (
May be invalid. results.
When considering our results, it is important to remember the three main limitations of this work.
First, we explored the test box size effect with only one material at a temperature and a depth.
Second, our load compaction may not be able to accurately simulate the effect of many children playing on the playground for a long time.
Third, due to the cost issue, we have not exceeded the minimum test specified in ASTM F1292-
That is to say, we only drop three drops at each height and material depth.
However, potential users of these playground materials need to be very cautious in explaining the test results of uncompressed looseness
Fill the surface material.
Although the readings of some materials are quite consistent, uncompressed gravel and sand produce unstable results.
The data show that the sand or gravel at 6 inch depth has better resilience (
Higher critical height)
More than 12 inch of the depth is counter-intuitive.
Although this test result may be accidental, it indicates that the current test method is for loose-
Fill in the material and it can produce such a discovery.
One possible explanation is that the critical height is based on the mean of the second and third descent.
In our tests, the second drop of uncompressed gravel reading at each height is always much higher than the first drop (
It is not uncommon to increase 150% to 200%)
, Indicates that the surface may have been replaced or compressed by the first drop.
However, the third drop tends to be less than the second, suggesting that the shifted material is back in the Dent again before the third drop.
Uncompressed sand shows unstable and unpredictable values based on the mean values of the second and third drops and the effects of temperature and depth.
The special differences between these sand and gravel raise questions about how these materials behave on the actual playground.
For these materials, the average number of additional drops may provide more representative test results.
For wood fibers, wood chips and chopped rubber, the average second and third drops appear to be appropriate and representative.
We found differences in the consistency and critical height of the results between uncompressed and compressed samples.
As the depth of the material increases, the compression state shows a fairly orderly increase in the critical height.
The difference in compression/uncompression is particularly noticeable for sand and gravel
That is, 10 of the 24 tests show that the critical height of the compressed surface is better.
Perhaps, compression reduces the amount of displacement that occurs between the three drops.
To see if compression can better represent loose-
Fill in the material properties under actual playground conditions.
Our critical height results are inconsistent with CPSC results, and 2 demonstrate the difference between 1 and greater than 3 feet (table 3).
For example, CPSC lists 5 feet as the critical height of 9 inch uncompressed sand (
Thin and thick)
Although this study obtained a critical height of 10 feettwice as high.
Although we only tested the effect of the box size with one material at a temperature and one depth, we and the other 6 studies, 8 shows that we can explain some of these differences by using a box of 18 × 36 inch, because its use can lead to a higher critical height.
We believe that larger boxes can better simulate the actual playground environment.
However, the impact of the box size needs to be further explored, as is the comparison of laboratory testing with real field conditions.
View this table: View inline View pop-up table 3 Effects of critical drop height on prevention by source and material depth our results indicate the need to improve ASTM F1292 loose material Standardfill materials.
The 5, 11 variables to consider include modifying the box size, better controlling the temperature conditions, adding compression components, and performing more drops to average the results.
At the same time, although consumers need to show caution in excessive consumption
According to the test results, our results show that the performance of crushed rubber is significantly superior, and the performance difference between sand, wood fiber and wood chips is very small.
The impact attenuation performance of pea gravel is the worst;
Compared to other available looseness
Filling materials, we believe that pea gravel is a relatively poor choice as a safe playground surface and should not be used under a 6 feet high equipment.
This publication has been supported by a grant of the number 17/ccu712119
02 from the Centers for Disease Control and Prevention (CDC).
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Consumer Product Safety Committee.
Safety Manual for public playground.
Washington, D. C. : Office of printing, US government, 1997.
Marshall chalmers, d j. , Marshall SW, Langley JD, et al.
Height and surface are risk factors for falling injury of playground equipment: case-control study. Inj Prev 1996; 2:98–104.
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Playground Safety
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American Association for Testing and Materials.
Standard Specification for impact attenuation of systems under and around the playground equipment, F1292-91.
Philadelphia, PA: ASTM, 1991.
Ramsey of Preston JD.
Impact attenuation performance of the playground paving material.
Washington: Consumer Product Safety Commission, 1990.
Consumer Product Safety Committee.
Safety Manual for public playground.
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Standard search and analysis report on children\'s outdoor play areas.
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Portland cement
Based on plaster, C897-88.
Philadelphia, PA: ASTM, 1988.
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Philadelphia, PA: ASTM, 1993.
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