Also in: Disaster Response and Recovery
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, 4 for a 6 ft Z359.13 lanyard) 4
- 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 18 ft
- Margin vs available 2
Checked against published worked examples from: ANSI/ASSP Z359.13 / OSHA 1926 Subpart M.
Details, formula, and sources
ScopeRFC = free-fall distance + deceleration distance + worker height (D-ring to feet) + safety margin. A 6 ft free fall, 4 ft deceleration (the ANSI Z359.13 48 in maximum for a 6 ft free-fall lanyard; OSHA caps the system at 3.5 ft), 5 ft worker, and 3 ft margin needs 18 ft. Enter each explicitly - free-fall depends on the anchor position; an SRL cuts both the free-fall and deceleration. Per ANSI Z359 / OSHA 1926 Subpart M; the equipment instructions and a competent person govern.
Formula or tablerequired_clearance below the anchor = anchor height above the D-ring + free_fall_distance + deceleration_distance + worker_height (D-ring to feet) + safety_margin (the first two together are the connector length); below the surface the worker stands on = free_fall_distance + deceleration_distance + safety_margin; margin = available_clearance - required_clearance; adequate when margin >= 0.
Source and editionANSI Z359.1 (Fall Protection Code) and OSHA 1926 Subpart M fall-clearance calculation, by name.
Free accessThe additive fall-clearance model is public (ANSI Z359 / OSHA 1926 Subpart M); OSHA standards are free at osha.gov, the Z359 standards are licensed.
What governsEstimate. AHJ and licensed fire protection engineer govern.
API field namesfree_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 distance up to 48 in (4 ft) for a 6 ft free-fall energy absorber and 60 in for a 12 ft one; OSHA limits the system to 3.5 ft; an SRL is usually lessANSI/ASSP Z359.13-2013; 29 CFR 1926.502(d)(16)(iv)
- Free-fall basis depends on the anchor position relative to the D-ring and the connector lengthfall-protection practice