Simplification and transformation of ASTM F1292 measurement procedure for fall accident injury criteria

Shock-absorbing aggregates beneath playground equipment: grain properties and moisture content

OBJECTIVES

To assess the influence of grain size distribution and moisture condition on aggregates'Setting and methodsImpact attenuation of sands and gravels was tested using a guided headform with a uniaxial accelerometer inside. The result for impact attenuation was the acceleration value of the headform measured from four different drop heights and the Head Injury Criterion (HIC) calculated from it. The acceptable HIC value of a shock-absorbing layer is <1000, that is, less than the critical fall height. Tests were conducted with both dry and wet materials.

RESULTS

The impact attenuation of a shock-absorbing layer made of loose aggregate is determined mainly by the following material factors: maximum grain size, median grain size, uniformity coefficient, fines content, grain shape and moisture content. In addition, the moisture content of aggregate, especially sands, has a major impact on its impact attenuation capacity. Of the studied sands, coarse and gravelly ones had the best impact attenuation properties. Most of the examined sands were uniformly graded. None of the grain properties of gravels proved more significant than the others. Yet, open-graded gravel (dominant grain size 4-8 mm) containing a small amount (about10%) of sand fraction 0.06-0.6 mm, but with hardly any coarse sand (0.6-2 mm), was found to have good impact attenuation.

CONCLUSIONS

This study shows that the aggregates for shock-absorbing layer should always be tested wet in laboratory conditions corresponding the most critical situation. Standards should include a procedure for wet testing of aggregates.

Accelerations relevant to blunt trauma: theory and data

Maximum acceleration and the head injury criterion (HIC) are both used as indicators of likely head injury severity. A dataset has previously been published of impacts of an instrumented missile on four ground surfaces having a layer of between 0 and 16 cm of sand. The dataset is compared with recently-developed theory that predicts power-function dependence of maximum acceleration and HIC on drop height. That prediction was supported by the data. The surfaces differed in respect of the exponents estimated.