Required Fall-Arrest Clearance (ANSI Z359)
The clearance a personal fall-arrest system needs below the anchor so the worker does not strike the level.
Example
You enter
- Free-fall distance (ft) 6
- Deceleration distance (ft, <= 3.5 lanyard) 3.5
- Worker height, D-ring to feet (ft) 5
- Safety margin (ft) 3
- Available clearance below anchor (ft, optional) 20
You get
- Required clearance below anchor 17.5 ft
- Margin vs available 2.5
Details, formula, and sources
RFC = free-fall distance + deceleration distance + worker height (D-ring to feet) + safety margin. A 6 ft free fall, 3.5 ft deceleration (the Z359 lanyard cap), 5 ft worker, and 3 ft margin needs 17.5 ft. Enter each explicitly - free-fall depends on the anchor position; an SRL cuts both the free-fall and deceleration. Per ANSI Z359.1 / OSHA 1926 Subpart M; the equipment instructions and a competent person govern.
required_clearance = free_fall_distance + deceleration_distance + worker_height (D-ring to feet) + safety_margin; margin = available_clearance - required_clearance; adequate when margin >= 0.
ANSI Z359.1 (Fall Protection Code) and OSHA 1926 Subpart M fall-clearance calculation, by name.
The additive fall-clearance model is public (ANSI Z359 / OSHA 1926 Subpart M); OSHA standards are free at osha.gov, the Z359 standards are licensed.
Estimate. AHJ and licensed fire protection engineer govern.
Field names used by the API: free_fall_distance_ft, deceleration_distance_ft, worker_height_ft, safety_margin_ft, available_clearance_ft, required_clearance_ft, margin_ft
- Additive model RFC = free fall + deceleration + worker height + safety marginANSI Z359 / OSHA 1926 Subpart M
- Deceleration cap 3.5 ft max energy-absorber stroke for a shock-absorbing lanyard; an SRL is much lessANSI Z359.1
- Free-fall basis depends on the anchor position relative to the D-ring and the connector lengthfall-protection practice