Fall clearance calculator
Short answerRequired fall clearance is free fall plus deceleration distance plus the height from the harness D-ring to the feet plus a safety margin. With a 6 ft lanyard anchored at D-ring height that is 6 + 3.5 + 5 + 2 = 16.5 ft (about 5.0 m) below the anchor. Less space means that system must not be used.
What the fall clearance calculator works out
Fall arrest equipment only works if there is room for it to stop the worker before they hit the ground, a lower level or an obstruction. The calculator gives the minimum clear distance needed below the anchor.
Choose a shock-absorbing lanyard or a self-retracting lifeline (SRL), then enter lanyard length, how far the anchor is above the D-ring, D-ring to feet height and a safety margin. The calculator works in metres.
The fall clearance formula
- Clearance = free fall + deceleration distance + D-ring to feet + safety margin
- Free fall (lanyard) = lanyard length minus anchor height above the D-ring
- Deceleration used by the tool: 3.5 ft (1.07 m) for a lanyard; 2 ft (0.61 m) for an SRL, which also uses 2 ft (0.61 m) of free fall
- Typical inputs: D-ring to feet 5 ft (1.5 m); safety margin 2 ft (0.6 m)
Worked example
Shock-absorbing lanyard, 6 ft long, anchor level with the D-ring: 6 + 3.5 + 5 + 2 = 16.5 ft (about 5.0 m). In metres, the calculator's defaults give 1.8 + 1.07 + 1.5 + 0.6 = 4.97 m (about 16.3 ft).
Move the anchor 2 ft above the D-ring and free fall drops to 4 ft: 4 + 3.5 + 5 + 2 = 14.5 ft (about 4.4 m).
With an SRL: 2 + 2 + 5 + 2 = 11 ft, or 0.61 + 0.61 + 1.5 + 0.6 = 3.32 m in the calculator.
How to read the result
Compare the result with the clear distance actually available below the anchor. If the space is smaller, change the system: move the anchor higher, switch to an SRL, or remove the fall hazard. OSHA limits that frame the inputs:
- Free fall no more than 6 ft (1.8 m), and no contact with any lower level (29 CFR 1926.502(d)(16)(iii) and 1910.140(d)(2)(ii)).
- Deceleration distance no more than 3.5 ft (1.07 m) (1926.502(d)(16)(iv) and 1910.140(d)(1)(ii)).
- Maximum arresting force 1,800 lb (8 kN) with a body harness.
- Anchorages rated 5,000 lb (22.2 kN) per worker, or designed with a safety factor of two under a qualified person (1926.502(d)(15)).
What the calculation does not tell you
- It uses typical deceleration values. The figures on your device label override them.
- It has no separate line for harness stretch and D-ring shift, often taken as about 1 ft (0.3 m). Add it to the margin or D-ring height.
- It ignores swing fall. Working to the side of the anchor adds a pendulum swing and can mean striking structures.
- It does not check anchor strength, rescue arrangements or suspension trauma. Plan rescue before work starts, and follow site procedures and a competent person.
Questions people ask
How do you calculate fall clearance?
Add the free fall distance, the deceleration distance of the energy absorber or SRL, the height from the D-ring to the worker's feet, and a safety margin. For a 6 ft lanyard anchored at D-ring height: 6 + 3.5 + 5 + 2 = 16.5 ft. Use the values on your equipment label.
What is the OSHA maximum free fall distance?
A personal fall arrest system must be rigged so the worker cannot free fall more than 6 ft (1.8 m) or contact any lower level (29 CFR 1926.502(d)(16)(iii)). General industry rules in 1910.140 allow longer free fall only where the manufacturer has designed and tested the system to keep arresting force at or below 1,800 lb.
What is the maximum deceleration distance?
OSHA limits the deceleration distance to 3.5 ft (1.07 m) in construction and general industry. Energy absorbers and self-retracting lifelines state their own maximum on the label, and that figure is the one to use in a clearance calculation, even when it is shorter than the regulatory limit.
Why does an SRL need less clearance?
A self-retracting lifeline stays short and locks within a short distance once a fall starts, so free fall and deceleration are both small. The calculator uses about 2 ft (0.61 m) for each. A shock-absorbing lanyard allows free fall up to its full length before the absorber starts working.
Does anchor height matter?
Yes. Every foot the anchor sits above the D-ring cuts free fall by a foot. An anchor below the D-ring, such as foot-level tie-off, increases free fall, and only lanyards rated for that use may be used there. Anchor overhead where you can.
What safety margin should I use?
A margin of 2 to 3 ft (0.6 to 0.9 m) is common practice. It covers harness fit, a taller than average worker and small measuring errors. Where your site procedure or the equipment manufacturer specifies a larger margin, use that figure instead.
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