# Additional Criteria for Playground Impact Attenuating Sand
## 1 Introduction  
Traditionally sand has been employed by engineers as select fill and used effectively as a compacted sub-base beneath pavements such as roads. This role for sand is opposite to what is required in children's playgrounds. For children's playgrounds, sand that is employed as an impact attenuating surface (IAS) must not compact and should remain uncompacted for its usable life. Moreover, IAS sand should remain uncompacted during and after rain or after the irrigation sprinklers have inadvertently doused it. It should not require raking to break a hard crust or compaction in high usage areas of the playground. Ideally, it should be self-levelling and maintenance-free except for periodic topping up and removal of litter and organic matter. There has been very little research into the parameters that are required for IAS sand used to reduce fall-related injuries within children's playgrounds. In 2004 [PERSON] and [PERSON] published a discussion paper on playground IAS [1]. More recently [PERSON] et al. published a paper on the dynamic behaviour of high performance sand surfaces used in the sports industry [2]. IAS sand is used within children's playgrounds to reduce the likelihood and consequences of death and serious injuries resulting from falls at height from playground equipment. There are standards around the world for the measurement of the performance of the IAS [3; 4; 5; 6; 7]. These standards are effective in the measurement of the IAS performance but do not provide guidance on the selection of what makes a good IAS sand. It is important that the IAS sand is fit-for-purpose andthat it meets the minimum safety requirements and is maintained to these standards for the life of the playground equipment [8]. [PERSON] et al. [9] showed that the amount of energy dissipating away from or returned to a child impacting onto a playground surface will influence the risk of sustaining a fracture. Up to 45% of accidents to children in playgrounds lead to serious injuries including concussions and bone fractures [10]. Furthermore, it is estimated that 67% of recorded playground injuries are due to falls from the equipment to the ground [11]. [PERSON] et al. [12] suggest that two key risk factors for playground related injury are the height of equipment from which children fall and the type of surfacing they land. Therefore, it seems appropriate that action needs to be directed at reducing the potential for children to fall from playground equipment and reducing the severity of these falls given the likelihood that they will occur. In preparation for this research, we undertook a literature review to consider different types of impact attenuation methods used in industry. The most widely applied test method for evaluating the impact attenuating performance of a playground surfacing material is to employ the methodology contained in the Australian Standard AS 4422:2016 [6], and its equivalent overseas standards [3; 4; 5] particularly the recently published ISO Technical Specification [7]. This process involves dropping an instrumented metal headform onto a sample of the material, with performance measured in terms of g-max and head injury criterion (HIC) parameters. [PERSON] et al. [13] highlight the inadequacies of this method for loose fill materials (including sand) on the basis of the inconsistency in the results that are achieved. Following the investigation of a variety of loose fill materials, they conclude that reproducibility of the process was a key problem. Despite these inadequacies, the method remains at the forefront of material selection processes for IAS materials used in playground safety. An objective of this research is to propose an accelerated aging test method to allow a quantitative assessment of how the sand will deteriorate over time, subject to use and external factors, in the context of children's playgrounds. A key industry to consider is the construction industry as it has a strong tradition of materials testing and supporting laboratories to conduct such testing.