Critical drop heights in feet for uncompressed materials, by source and material depth
| Depth (inches) | Source | Gravel | Sand | Wood chips | Wood fibers |
|---|---|---|---|---|---|
| CPSC = Consumer Product Safety Commission. | |||||
| 6 | CPSC2 | 6 | 5 | 7 | 6 |
| This study | 6 | 10 | 8 | 8 | |
| 9 | CPSC2 | 7 | 5 | 10 | 7 |
| This study | 5 | 10 | 11 | 10 | |
| 12 | CPSC2 | 10 | 6–9 | 11 | >12 |
| This study | 5 | 8 | 12 | 12 | |