How to calculate required fall clearance
A harness and lanyard only work if there is enough open space below the anchor. If the ground, a beam or stacked material sits closer than the arrest distance, the energy absorber never finishes deploying and the worker strikes the obstruction. This calculator adds up the vertical distance a fall actually consumes.
Required clearance is free fall distance + deceleration distance + worker height from D-ring to feet + safety margin. Using the OSHA 1926.502 ceilings of 6 ft free fall and 3.5 ft deceleration, with a 6 ft worker and a 3 ft margin, you need about 18.5 ft of clear space below the anchor. Where that is not available, a self-retracting lifeline or a higher anchor is the fix, not a shorter margin.
OSHA 1926.502(d)(16) requires a personal fall arrest system to limit free fall to 6 feet, limit deceleration distance to 3.5 feet, and prevent contact with any lower level. Anchoring above the D-ring cuts free fall and arrest forces together, while a foot-level tie-off roughly doubles the fall distance and can exceed the 6 ft limit on its own.
Deceleration distances differ by product, so take the value from the manufacturer label rather than a rule of thumb. Treat the result as a planning check only: anchor strength, swing fall hazards, rescue provisions and the rest of the fall protection plan should be reviewed by a qualified person as OSHA defines the term.
Frequently asked questions
Free fall distance, deceleration distance as the energy absorber deploys, the worker height from D-ring to feet, and a safety margin. If the ground or an obstruction is closer than that total, the worker strikes it.
A personal fall arrest system must limit free fall to 6 feet or less and deceleration distance to 3.5 feet or less, and must not let the worker contact a lower level.
Avoid it. A low anchor increases free fall, arrest forces and required clearance at the same time. Anchor above the D-ring whenever the structure allows it.