Playground Surface Impact Budgets from Local Materials: Minimum Maintained Depths, Degradation over a School Term, and Cost per Child

SIMULATED, NOT MEASURED. A design method modelling head-impact attenuation (peak deceleration and Head Injury Criterion, thresholds 200 g and HIC 1000) for falls of 1.0-2.5 m onto loose sand, wood chips, shredded rubber, grass over soil and compacted earth, calibrated to published ASTM F1292 / EN 1177 / CPSC ranges. Derives minimum maintained depths (at 2.5 m: 230 mm sand, 175 mm wood chips, 110 mm shredded rubber; grass and compacted earth fail at higher heights), degradation and maintenance intervals over a school term (top-up every about 5-6 weeks for sand and wood chips plus weekly raking of displaced material), failure cases (rain-compacted sand, swing-exit displacement, frozen or baked surfaces), and cost per child per year ($3.56 wood chips, $4.66 sand, $7.47 shredded rubber for a 200-child reference school). All numbers are outputs of the accompanying compute.py.