A 6-foot shock-absorbing lanyard needs roughly 17 feet of open space below the anchorage — not 6, and not 10. The lanyard is only the first of four distances that stack up while a fall is being arrested. Get the total wrong and the harness works exactly as designed while the worker still hits the deck.
What fall clearance actually means
Fall clearance is the vertical room a personal fall arrest system needs to do its job: the distance from the anchorage connection point straight down to the first thing a falling worker could hit. Not the ground, necessarily — the nearest obstruction. A stack of block, the bed of a truck, a scaffold plank, the boom of a lift parked underneath.
OSHA does not publish a clearance number, because there is not one to publish. What the standard says is the outcome you have to achieve. Under 29 CFR 1926.502(d)(16)(iii), a personal fall arrest system must be rigged so an employee can neither free fall more than 6 feet nor contact any lower level. The second half of that sentence is the clearance rule, and it is where the arithmetic comes in.
It matters more than most crews assume. Fall protection — general requirements (1926.501) has led OSHA's list of most frequently cited standards for years, and a harness that arrests a fall two feet above a concrete slab is a paperwork pass and a field failure at the same time.
The four distances that stack up
Manufacturers all draw the same picture, and 3M states it as a formula in its published clearance chart: the required distance below the anchorage connection point is RD = LL + DD + HH + C. Each term is a real distance the worker's body travels or occupies once the fall is over.
| Term | Distance | Common value | Where the number comes from |
|---|---|---|---|
| LL | Lanyard length | 6 ft | Printed on the lanyard. This is its length before the energy absorber deploys. |
| DD | Deceleration distance | 3.5 ft | How far you keep travelling while the energy absorber stops you. 3.5 ft (1.07 m) is the maximum OSHA allows under 1926.502(d)(16)(iv); your label may say less, and some manufacturers publish more in their charts to stay conservative. |
| HH | Height of the suspended worker | 6 ft | Back D-ring down to the soles of the boots. Your feet are the part that hits first. |
| C | Safety factor | 1.5 ft | Covers D-ring slide and harness stretch during arrest, plus the error in your own tape measure. Plenty of employer programs use 3 ft. |
Add them: 6 + 3.5 + 6 + 1.5 = 17 feet. 3M's own worked example on the same chart lands at 17.5 ft because it allows 4 ft of deceleration distance rather than 3.5. Neither number is a rule — they are what these four inputs produce, and the ones on your equipment govern. The fall clearance calculator runs the same arithmetic against the clearance you measured and tells you whether it fits.
Free fall, total fall, and the 6-foot limit
Two different distances get called "the fall," and mixing them up is how crews end up with the wrong answer.
- Free fall distance is how far you drop before the system starts to slow you down: the lanyard length, plus however far your back D-ring sits above the anchorage. This is the distance 1926.502(d)(16)(iii) caps at 6 feet.
- Total fall distance adds the deceleration distance on top. Appendix C to Subpart M is explicit that the stretch of the lanyard and the stopping distance of the deceleration device "must be added to the free fall distance to arrive at the total fall distance before an employee is fully stopped," and that enough distance must be kept between the worker and the obstructions below.
- Required clearance adds the worker's own body and the safety factor to that, because the fall is not over until the boots stop moving.
The free fall limit exists because of force, not distance. A longer free fall means more energy for the absorber to soak up, and 1926.502(d)(16) caps the arresting force at 1,800 lb with a body harness. Appendix C (k) asks you to keep free fall to a minimum rather than simply staying under the cap.
Where you tie off changes the free fall — not the clearance
This is the part that surprises people. Raising the anchorage shortens the free fall dramatically and cuts the arresting force with it. It does not reduce the room you need below the anchor, because after arrest you are still hanging a lanyard, an absorber and a body length beneath it.
| Setup | Free fall | Clearance needed below the anchorage |
|---|---|---|
| 6 ft lanyard, anchorage level with the D-ring | 6.0 ft | 17.0 ft |
| 6 ft lanyard, anchorage 2 ft overhead | 4.0 ft | 17.0 ft |
| 4 ft lanyard, anchorage 2 ft overhead | 2.0 ft | 15.0 ft |
| 6 ft lanyard tied off at the walking surface, D-ring 5 ft above it | 11.0 ft | 17.0 ft |
The last row is the one to stare at. Appendix C (k) works through exactly that case: with a 6-foot lanyard tied off at the working level, the free fall is the 6 feet of lanyard plus the distance from that level up to the attachment point on your back. Around 11 feet, against a 6-foot limit. The clearance may well be there; the rigging is still not acceptable.
And the only line in the table where the required clearance drops is the one where the connecting device got shorter. That is the lever worth pulling when the room underneath is tight.
One more thing the arithmetic does not see: swing fall. Anchor off to the side and a falling worker pendulums, travelling further than the vertical numbers suggest and arriving at whatever is beside them. Appendix C (m) tells you to choose tie-offs that minimize it. Directly overhead is the answer to several problems at once.
Five ways crews run out of clearance
- Measuring to the ground instead of to the obstruction. The scaffold platform, the material stack or the parked lift is the lower level for this calculation.
- Forgetting the worker's own height. Six feet of body hangs below the D-ring. It is the single largest term after the lanyard and the easiest to leave out.
- Using the lanyard's length as the clearance. A "6-foot lanyard" describes the strap, not the fall.
- Tying off low because the anchor is convenient. A foot-level tie-off with a 6-foot lanyard blows past the free fall limit before you get to clearance at all.
- Checking once, at the start of the job. Decking a floor, moving a lift, or stacking material underneath changes the answer while the harness stays exactly the same.
A sixth, quieter one: equipment that has already taken a fall. A system subjected to impact loading has to be removed from service immediately under 1926.502(d)(19), and inspection before each use is required by (d)(21). Our harness and lanyard inspection form lists the defects to look for and prints on Letter paper.
What to do when the room is not there
Do not shave the safety factor. Change the system — in roughly this order of preference:
- Eliminate the exposure. Guardrails, a hole cover meeting 1926.502(i), or a floor system need no clearance below and no rescue plan.
- Use travel restraint. A connecting device short enough that you physically cannot reach the edge means there is no fall to arrest.
- Shorten the connecting device. A 4-foot lanyard removes 2 feet from the requirement; a self-retracting lifeline with a short arrest distance removes considerably more, and its clearance comes from its own label.
- Raise the anchorage. It will not reduce the clearance you need, but it cuts free fall and arresting force, and it is usually the cheapest change on site.
- Change the work. Do the task from a lift, from the ground, or from a platform with guardrails.
Whatever you land on, write it down where the crew will see it. Record the anchorage, the device and the measured clearance in the pre-task plan or the job hazard analysis for that task, so the next shift is not re-deriving it from memory.
Two duties sit alongside the clearance check and are separate from it. The anchorage must be independent of any anchorage used to support or suspend platforms and capable of supporting at least 5,000 lb per employee attached, or designed by a qualified person with a safety factor of at least two — 1926.502(d)(15). And the employer must provide for prompt rescue — 1926.502(d)(20). A worker hanging in a harness is not a resolved situation.
Bottom line
- Required clearance = lanyard + deceleration distance + worker height + safety factor, measured below the anchorage. Roughly 17 ft for a 6-foot lanyard.
- Free fall is capped at 6 ft in construction, and the system must also keep the worker off any lower level — 1926.502(d)(16)(iii).
- Anchoring overhead cuts free fall and arresting force. Only a shorter connecting device cuts the clearance you need.
- Measure to the nearest obstruction, in the worst position on that anchorage, and re-check when the space below changes.
- The label on your own equipment beats every generic number in this article.