Fall clearance calculator
- Free fall = lanyard length − anchor height above the D-ring
- Free fall: 6 − 0 = 6 ft (6 ft limit met)
- Clearance = free fall + deceleration distance + harness stretch + D-ring to feet + safety margin
- Put in the numbers: 6 + 3.5 + 1 + 5 + 2
- Answer: 17.5 ft of clearance below the working surface
Starting values are examples only. OSHA sets the 6 ft and 3.5 ft limits; stretch, D-ring height and margin come from the equipment maker and the worker.
Formula and sources
- Free fall = lanyard length − anchor height above the D-ring (≤ 6 ft)
- Clearance = free fall + deceleration (≤ 3.5 ft) + stretch + D-ring to feet + margin
The formula comes from
29 CFR 1926.502(d)(16)(iii)-(iv)(opens ecfr.gov in a new tab)“(iii) be rigged such that an employee can neither free fall more than 6 feet (1.8 m), nor contact any lower level; (iv) bring an employee to a complete stop and limit maximum deceleration distance an employee travels to 3.5 feet (1.07 m); and,”
The formula comes from
29 CFR 1926.502(d)(16)(ii)(opens ecfr.gov in a new tab)“limit maximum arresting force on an employee to 1,800 pounds (8 kN) when used with a body harness;”
Formulas and calculators on the BCSP exams
- BCSP gives you no formula sheet, and you can't bring one.
- When a question needs a formula, the formula is written into the question, unless the question is testing whether you know that formula.
- You get an on-screen calculator that works like the TI-30XS, plus a whiteboard. You can't bring your own calculator.
- On the ASP, Mathematical Calculations is its own domain, worth 10% of the exam (ASP11 blueprint).
BCSP on formulas
BCSP, What to Expect When Sitting for a BCSP Exam (item 7)(opens bcsp.org in a new tab)“For any question requiring a mathematical formula, the formula will be included within the exam question (unless the question is specifically testing your knowledge of a formula). You will not be provided or permitted to bring a formula sheet.”
BCSP on calculators
BCSP, What to Expect When Sitting for a BCSP Exam (item 6)(opens bcsp.org in a new tab)“You will be provided an on-screen calculator, emulating the TI-30XS scientific calculator. You will also have access to a white board and dry erase marker. The testing center will not provide a physical calculator or permit candidates to bring their own.”
FAQ
How do you calculate fall clearance?
Add the free fall distance, the deceleration distance, harness stretch and D-ring shift, the distance from the D-ring to the worker's feet, and a safety margin. The total must be less than the distance to the level below.
What are OSHA's limits for a personal fall arrest system?
In construction, 1926.502(d)(16) says the system must keep free fall to 6 ft or less, keep the worker from contacting any lower level, limit deceleration distance to 3.5 ft and, with a body harness, limit arresting force to 1,800 lb.
How do you find the free fall distance?
Free fall is the lanyard length minus how far the anchor is above the D-ring. A 6 ft lanyard anchored at D-ring height gives 6 ft of free fall. Anchoring 2 ft below the D-ring gives 8 ft, which is over the limit.
Where do the stretch, D-ring and margin numbers come from?
1926.502 doesn't set them as numbers. Use the figures from the equipment maker's instructions and the worker's own height. The starting values in the calculator are only examples.
This tool is for study and estimates. Follow the equipment maker's instructions and a competent or qualified person's review. It doesn't cover swing falls, horizontal lifelines or self-retracting lifelines.