Why sag matters
A flexible horizontal lifeline deflects under fall arrest forces. Extra sag increases required clearance below the walking surface. A common cable approximation is:
Sag ≈ (w × L²) ÷ (8 × T) where w is line load, L span, and T tension.
Horizontal Lifeline Sag Calculator
Horizontal lifeline · sag + clearance
Estimate midspan sag with a simple cable model and add free fall, deceleration, and safety into clearance. Use manufacturer charts for real systems.
Formula: Sag ≈ (w × L²) ÷ (8 × T) · Clearance ≈ Free fall + Decel + Sag + Safety
- Engineered HLL systems supersede this estimate.
- Respect simultaneous-user limits.
- Anchorage strength is a separate design check.
Frequently asked questions
Is this engineered HLL design?
No. Manufacturer systems and competent design control real installations. This is a teaching / planning estimate.
Multiple users?
Most systems limit simultaneous users — follow the system manual, not this estimate alone.
Energy absorbers?
Inline absorbers change tension and sag — use manufacturer clearance charts when available.
Pair with fall clearance?
Yes — add sag to free fall, deceleration, harness stretch, and safety factor.
