How the fall clearance calculation works
When a worker falls, the D-ring on their back drops through several distances in a row. Clearance is the sum of those distances, because the worker must stop before reaching the level below:
- Free fall is the drop before the system starts to catch the worker. For a lanyard it is the lanyard length less the height of the anchor above the D-ring, and never below zero. An anchor below the D-ring adds that drop on top of the lanyard length. Section 1926.502(d)(16)(iii) limits free fall to 6 feet.
- Deceleration distance is how far the shock absorber lets the worker travel while it stops them. Section 1926.502(d)(16)(iv) caps it at 3.5 feet. Many lanyards are labelled lower, so use the label. For an SRL, enter its arrest distance from the manual instead.
- D-ring shift covers harness stretch and the D-ring sliding up the back under load.
- D-ring to feet is how far the feet hang below the D-ring once the worker is stopped.
- Safety factor is a cushion on top, so a worker who stops does not stop on the floor below. Teams pick a figure by site rule.
The D-ring starts above the walking surface by the same D-ring to feet distance, so the tool adds that to your surface height before it compares. A SHORT result means the worker could reach the level below or an obstruction before the system holds them. This calculator assumes a straight drop below the anchor. Working off to one side can add a swing, so follow your maker's instructions for that case. Read the full rule set in the OSHA fall protection (Subpart M) guide.
Worked example 1: shock lanyard, anchor at D-ring height
A 6 ft lanyard, an anchor at D-ring height and a 3.5 ft deceleration distance. Free fall = 6 ft. Required = 6 + 3.5 + 1 (D-ring shift) + 5 (D-ring to feet) + 2 (safety factor) = 17.5 ft below the D-ring. The worker stands on a surface 15 ft above the level below, so the D-ring is 15 + 5 = 20 ft above it. Spare clearance = 20 − 17.5 = 2.5 ft.
Worked example 2: the same lanyard tied off at the feet
Move the anchor to foot level, 5 ft below the D-ring. Free fall = 6 + 5 = 11 ft, which is over the 6 ft limit. Required = 11 + 3.5 + 1 + 5 + 2 = 22.5 ft against the same 20 ft, so the worker is 2.5 ft short. An SRL anchored overhead with a 2 ft arrest distance (an example figure) needs 0 + 2 + 1 + 5 + 2 = 10 ft. These are original arithmetic examples, not exam questions.
Fall clearance questions
Is the 3.5 feet in OSHA the clearance I need?
No. It is the most a system may let the worker travel while it stops them. Clearance adds free fall, D-ring shift, the hang below the D-ring and your safety factor on top of it, which is why a 6 ft lanyard can need around 17 ft or more.
What do I enter for D-ring shift and safety factor?
Use the figures in your harness and connector instructions for the shift, and your site or company rule for the safety factor. This tool does not set them for you, which is why they are plain inputs you can change.
When does an SRL need less clearance than a lanyard?
An SRL anchored overhead has little or no free fall and usually a shorter arrest distance, so the stack is shorter. Enter the arrest distance from its label or manual. If the anchor is below the D-ring, the tool adds that drop as free fall.
Falls and fall protection equipment sit in Domain 1 of the CHST blueprint. Working this arithmetic by hand is a good way to learn why anchor height and free fall matter.