Yes, he will be safe.
Here is how to calculate total fall distance and free fall distance.
Lanyard length: | 6.0 ft. |
Shock absorber deceleration distance: | 3.5 ft. |
Height to back D-ring: | + 5.0 ft. |
Necessary clearance: | 14.5 ft. |
Connection height: | – 10.0 ft. |
Total Fall distance: | 4.5 ft. |
Shock absorber deceleration distance: | – 3.5 ft. |
Free fall distance: | 1.0 ft. |