For a two-rope anchorage system, which statement correctly summarizes the minimum MBS requirement?

For a two-rope anchorage system, which statement correctly summarizes the minimum MBS requirement?

• A. 12 kN (2700 lbf)
• B. Twice the maximum arrest force of the backup system
• C. The greater of 12 kN (2700 lbf) and twice the maximum arrest force of the backup system
• D. 24 kN

Answer: (C)

In a two-rope setup, the anchor must be strong enough to handle the load from both lines during a fall arrest. There’s a baseline minimum strength of 12 kN to ensure a safe floor, and there’s also the possibility that the backup line could arrest a fall with a maximum force Fmax. Since two rope legs could load the anchor, the worst-case combined load can reach twice that arrest force. Therefore the required minimum MBS is the greater of 12 kN and 2 × Fmax. If Fmax is 6 kN, both values are 12 kN, so 12 kN suffices; if Fmax is higher, the needed MBS rises accordingly. That’s why the correct statement is the greater of 12 kN and twice the maximum arrest force of the backup system.

In a two-rope setup, the anchor must be strong enough to handle the load from both lines during a fall arrest. There’s a baseline minimum strength of 12 kN to ensure a safe floor, and there’s also the possibility that the backup line could arrest a fall with a maximum force Fmax. Since two rope legs could load the anchor, the worst-case combined load can reach twice that arrest force. Therefore the required minimum MBS is the greater of 12 kN and 2 × Fmax. If Fmax is 6 kN, both values are 12 kN, so 12 kN suffices; if Fmax is higher, the needed MBS rises accordingly. That’s why the correct statement is the greater of 12 kN and twice the maximum arrest force of the backup system.