Critical heights in feet for loose-fill materials, by compression status, Fahrenheit temperature, and material depth
| Depth (inches) and compression status | Gravel | Sand | Wood chips | Wood fibers | Rubber | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 30° | 72° | 120° | 30° | 72° | 120° | 30° | 72° | 120° | 30° | 72° | 120° | 30° | 72° | 120° | |
| Uncompressed | |||||||||||||||
| 3 | 4 | 3 | 5 | 7 | 6 | 6 | 4 | 4 | 4 | 5 | 5 | 4 | 4 | 3 | 4 |
| 6 | 8 | 6 | 7 | 12 | 10 | 9 | 8 | 8 | 6 | 9 | 10 | 8 | 12 | 12 | 12 |
| 9 | 6 | 5 | 8 | 11 | 10 | 12 | 10 | 11 | 9 | 12 | 12 | 10 | 12 | 12 | 12 |
| 12 | 9 | 5 | 8 | 12 | 8 | 10 | 12 | 12 | 12 | 12 | 12 | 12 | 12 | 12 | 12 |
| Compressed | |||||||||||||||
| 3 | 5 | 5 | 4 | 7 | 6 | 6 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 5 | 3 |
| 6 | 4 | 4 | 4 | 8 | 12 | 10 | 8 | 6 | 6 | 8 | 7 | 7 | 12 | 12 | 12 |
| 9 | 8 | 6 | 5 | 10 | 12 | 10 | 10 | 9 | 8 | 11 | 9 | 10 | 12 | 12 | 12 |
| 12 | 9 | 8 | 6 | 12 | 11 | 12 | 12 | 12 | 12 | 12 | 12 | 12 | 12 | 12 | 12 |