As is well known, playgrounds must have suitable and, above all, standard-compliant impact attenuating surfacing installed to ensure adequate safety for the children using them, e.g. in the event of a fall from a piece of playground equipment. There are different types of impact attenuating surfaces, which are presented in the standard and vary, for example, in terms of costs, minimum installation thicknesses and cleaning and maintenance requirements. It should, however, be noted that the most important property of these surfaces is impact attenuation, which is relevant to safety. This is the playground surface’s ability to dissipate the kinetic energy of an impact that is produced when a child falls from a piece of playground equipment. In this way, the risk of a critical, i.e. life-threatening, injury to the falling child is largely eliminated. The impact-attenuating properties are determined using a special test method based on the determination of the HIC value in accordance with DIN EN 1177:2018 (Impact attenuating playground surfacing – Methods of test for determination of impact attenuation, German version of EN 1177:2018). “HIC” stands for head injury criterion and the HIC value is a criterion used in technical investigations to assess the likelihood and severity of head injuries arising from an impact involving acceleration. Among other things, it plays an important role in motor vehicle safety (“crash tests”), but also in the requirements for impact attenuating playground surfacing. The higher the HIC value in the event of an impact, the higher the risk for the affected person to suffer a serious head injury. The limit value for playground surfacing tests is a HIC value of 1000, which at the same time defines the maximum drop height. The latter is determined by corresponding test methods in which a head impact is technically simulated. In addition to the HIC value, there is also the “gmax” value, which was also added as an independent parameter in the last revision of the standard. In physics, “g” stands for gravity and indicates the acceleration upon impact. Even though this value is already included in the calculation of the HIC value, since the last revision of the standard it must also be taken into account independently during measurements and has a limit value of 200. These two limit values help to ensure that the risk of serious head injuries in the event of a fall from the respective height onto the tested impact attenuating surfacing is as small as possible – but it cannot be ruled out completely. Nevertheless, these values help to assess the risk and keep it to a minimum.
As mentioned above, technical tests are carried out to determine the impact attenuation of a surface. The standard distinguishes between two methods of impact tests:
The first method is used to determine the critical fall height to enable full and detailed confirmation of the range of suitability of a product (surfacing) and it is usually carried out in a testing laboratory. In this case, a test specimen of the impact attenuating surfacing material under test is subjected to a simulated practical test by being struck by an instrumented headform in a defined series of impacts from different drop heights. The signal emitted by an accelerometer in the headform during each impact is processed to yield a severity from the measured impact energy, defined as head injury criterion. The HIC of each impact is plotted and the critical fall height is determined as the lowest drop height producing a HIC value of 1000 or a gmax value of 200. The results of this test method can be used, on the one hand, to determine the maximum drop height for which a particular impact attenuating surface is suitable and, on the other hand, to determine - for specific projects depending on the intended playground equipment and its free height of fall – the selection of suitable impact attenuating surfacing.
The second method describes an on-site drop test to enable confirmation as required of the performance of the surfacing in that specific site location (with the specified free height of fall of the installed playground equipment) at the time of the test. This means that the usability of the impact attenuating surfacing is tested directly in the installed condition. However, the way the testing is done is essentially the same as in the first method, except that it is not carried out under “laboratory conditions”.
If, after successful testing, an impact attenuating surface is found to be suitable for a specific project or drop height, it is essential that this result is properly documented afterwards. The basis of any suitability assessment should therefore be a test report by an ISO 17025 accredited testing institute or testing laboratory. This ensures qualification, verification and comparability.
In strict compliance with EN 1177, such a test report shall include the following:
1. number and date of this European Standard, i.e. EN 1177:2018;
2. a full description of the product tested;
3. a photograph of the material tested, with an indication of the scale of loose particulate material;
4. the method of fixing used to retain the samples or the internal dimension of the test container used and the layer thickness for loose particulate material;
5. a diagram showing all the test positions;
6. the condition of the surfacing at the time of the test (e.g. temperature and moisture content);
7. the results from each drop test, giving all drop heights used and the corresponding HIC and gmax values for each;
8. the critical fall height for the surfacing tested, expressed in metres to two decimal places and stating an uncertainty of ±7 %;
9. the curves of HIC and gmax vs. drop height from which the critical fall height of the surfacing was determined;
10. the time/acceleration curve of one impact with HIC or gmax.
In addition, it should be noted that the standard is regularly revised and republished. Test reports
used to prove the suitability of the impact attenuating surfacing should therefore always comply with the latest version of the EN 1177 standard.
About the author:
In addition to being a laboratory manager, expert and managing director of the Institut für Sportstättenprüfung ISP GmbH (Institute for Sports Facility Testing), Dennis Frank is also a member of several standards committees. ISP GmbH tests indoor and outdoor playground and sports surfaces for safety. Whether synthetic surfaces, artificial turf systems, sports hall floors or impact walls – they use a certified measuring method to analyse both existing surfaces and the suitability of new products.
Fall protection surfaces vary in terms of cost, minimum installation thickness and cleaning and care requirements. It should be noted that the most important property of these surfaces is the safety-related shock absorption. This is the surface's ability to reduce the impact energy that occurs when a child falls from a piece of play equipment. It prevents a critical, even life-threatening, injury.
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