Since loose-fill material (sand, pea gravel, wood products) is more likely to erode or become displaced, it is vital to maintain its depth on playgrounds because thicker loose-fill surface depths cushion falls and help prevent injuries. The required depth of loose-fill surfacing depends on both the surface material used and the potential fall height of installed equipment, so it is not possible to offer a simple recommendation.

Loose-fill surfaces require frequent maintenance to maintain optimal performance, which is decreased due to age, usage, erosion, and weathering. The lack of maintenance may lead to unintended injuries as children fall onto surfaces that do not provide appropriate cushioning. 

The National Program for Playground Safety conducted field testing on wooden loose-fill surfacing material (engineered wood fiber, wood chips, and wood mulch), as well as sand and pea gravel.

Wood products are the most widely used type of loose-fill material, and require the most shallow depth of material to protect against injuries from a given fall height, including the best performance at fall heights above 9 feet. Wood products’ ability to cushion a fall is less affected by erosion than sand and pea gravel.

Sand was found to require the most surface depth to cushion falls, while pea gravel displayed the greatest tendency to disperse and yield inconsistent surface depths. Both effectively cushion falls below 9 feet, but performance was found to decrease above 9 feet.  

Due to the expected degradation of impact-absorption performance for loose-fill surfaces (due to age, usage, and weathering), we recommend extra depth of surfacing materials in high-traffic and high-erosion areas. Additionally, maintenance intervals should be monitored and adjusted according to periods of high playground use, or harsher weather, particularly to maintain consistent surface depths. Avoid using equipment if the surfacing is notably eroded or worn, and contact your playground’s facility team (often municipal facilities managers or school officials) to request maintenance.