Setting the safety criteria

Soon afterwards, research in America established the medical criteria needed to prevent brain injuries in falls. The crucial factor was found to be deceleration.  If the deceleration of a child’s head as it struck the ground could be limited to 50 g (fifty times the force of gravity), permanent brain injury was very unlikely.  This became the basis of new British and then European Standards for impact-absorbing playground surfacing.

From then on the performance required of a playground surface was clear. It must have just the right elastic properties, neither too soft nor too hard, to maintain deceleration below 50 g.  And it must be thick enough to go on deforming progressively until the child’s head was safely brought to rest.

Achieving the performance was relatively easy. But the considerable thickness of resilient material required under high play equipment – typically 150 mm for a fall height of 3 m – made the first products very expensive.