Fall Arrest System — Free Fall, Deceleration & Clearance

Fall Arrest System

Free-fall distance 1.20 m

Worker + gear mass 90 kg

Absorber deceleration distance 1.07 m

Anchor height above lower level 6.0 m

Live Readouts

Set parameters, then Drop

Impact velocity (v)

0.0 m/s

Avg. arrest force

0.0 kN

Required clearance

— m

Available clearance

— m

How it works

A personal fall-arrest system has three stages: free fall (gravity only, until the lanyard/lifeline goes taut), deceleration (the energy absorber tears or the SRL brake pays out webbing, converting kinetic energy into heat/friction), and arrest (the worker stops, suspended).

Impact velocity:     v = √(2·g·FF)
Avg. arrest force:   F = m·g + m·v² / (2·DD)
Required clearance:  RC = FF + DD + 0.3 m (harness stretch) + 1.0 m (safety factor)

FF — free-fall distance before the device engages. OSHA 1926.502 caps this at 1.8 m (6 ft).
DD — deceleration distance: how far the absorber is designed to deploy while bringing the worker to a stop.
F — the average force transmitted to the body during arrest. OSHA caps this at 8 kN (1,800 lbf) for a full-body harness.
RC vs available anchor height — if the required clearance exceeds the height of the anchor above the ground or the next lower level, the worker strikes it before the absorber finishes deploying, even though the math above "arrests" the fall on paper.

A shock-absorbing lanyard typically allows more free fall (rigged overhead, ~0.6–1.8 m) but has a long, low-force deceleration webbing (up to ~1.07 m). A self-retracting lifeline (SRL) locks almost immediately (FF ≈ 0.3–0.6 m) but decelerates over a much shorter internal brake distance — both must still satisfy the same clearance and force limits.

Ready

Lanyard / lifeline Energy absorber Required-clearance zone

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