$$\text{Free Fall} \le 6\text{ ft}$$

$$\text{Deceleration} \le 3.5\text{ ft}$$

$$\text{Harness Stretch} = 1\text{ ft}$$

$$\text{Safety Factor} = 2\text{ ft}$$

$$\text{Total Clearance} = 6 + 3.5 + 1 + 2 = 12.5\text{ ft}$$