3.2 Fall clearance and swing falls

1 What has to fit under your feet

Fall clearance is the vertical distance required below the anchorage for the system to stop the worker before anything else does. It is a sum, and every term in it is real.

OSHA sets two of those terms — 6 feet of free fall and 3.5 feet of deceleration — and leaves the others to the equipment maker, which is why the required clearance figure printed on the label of one manufacturer's lanyard differs from another's. Use the instructions that came with the equipment you are actually wearing. Any number in a training course, including the worked example below, is illustrative.

2 A worked example, with the assumptions labeled

Take a worker of average build with a 6-foot shock-absorbing lanyard, tied off to an anchor at the level of the dorsal D-ring — a common real-world arrangement, and not a good one.

Seventeen and a half feet. That is the number that makes the whole exercise worthwhile, because it explains three things at once. It explains why a 6-foot lanyard on a scissor lift platform 12 feet up is a fatal combination. It explains why steel erection sets its trigger at 15 feet rather than 6. And it explains why self-retracting lifelines exist.

3 Anchor height changes everything

The single largest term in that sum is free fall, and free fall is set almost entirely by where the anchor is relative to the dorsal D-ring.

Anchoring at foot level with a 6-foot lanyard is not a marginal choice — it exceeds the 6-foot free fall limit in 1926.502(d)(16)(iii) on its own, before you consider anything else. If the only available anchor is at or below your feet, the fixed-length shock-absorbing lanyard is the wrong connector for that job.

4 Self-retracting devices: different arithmetic, not zero arithmetic

A self-retracting lifeline pays out and takes up like a seat belt and locks when it accelerates, so the free fall term collapses to whatever slack existed plus the distance the brake needs to engage. 1926.502(d)(12) recognizes devices that automatically limit free fall to 2 feet or less and requires them to sustain 3,000 pounds; (d)(13) covers devices that do not, and requires 5,000 pounds.

The clearance still has to be calculated. An SRL's arrest distance depends on the device, the worker's weight, and where the device is mounted, and the required clearance is stated in the manufacturer's instructions — often substantially less than a shock-absorbing lanyard needs, but never nothing. Two situations demand extra care:

• Mounted below the D-ring. Many SRLs are rated for overhead mounting only. A device clipped at foot level allows a free fall the brake was never designed to catch, and the required clearance grows sharply. Some devices are specifically rated for foot-level or leading-edge use and say so on the label; most are not.
• Over an edge. A cable or webbing line pulled across a slab edge or deck flute during arrest sees loading and abrasion no ordinary SRL is tested for. Leading-edge-rated devices exist for exactly this. 1926.502(d)(11) requires lifelines to be protected against being cut or abraded, and this is the case it was written for.

5 Swing fall

If the anchor is not directly above you, a fall becomes a pendulum. You drop, then swing, and the two hazards are additive: you can strike a wall, a column, a stack of material or the structure below at speed, and the swing also means your lowest point is below where the vertical calculation put you, because you are moving along an arc.

There is no OSHA number for swing fall — no maximum angle in the standard. What there is instead is the requirement in 1926.502(d)(16)(iii) that the employee not contact any lower level, and the general duty to plan the work. The practical control is geometry:

1. 1
   Keep the work close to plumb under the anchor. The further you move sideways, the larger the arc.
2. 2
   Move the anchor, not the worker. Two anchors and a re-tie beats one anchor and a 30-foot side reach.
3. 3
   Use a horizontal lifeline or a rail where the work is genuinely linear — designed under the supervision of a qualified person with a safety factor of at least two, per 1926.502(d)(8).
4. 4
   Add clearance for the swing. The arc puts you lower than the straight-line sum; if the vertical figure is tight, a swing makes it insufficient.
5. 5
   Clear the arc. If a swing is unavoidable, know what is in it and remove what you can.

6 Lifts, low heights and the honest answer

Aerial and scissor lifts are where clearance arithmetic most often produces an uncomfortable conclusion. On a scissor lift 12 feet up, no fall arrest arrangement anchored to the platform has room to work: the required clearance exceeds the working height. That is precisely why 1926.453(b)(2)(v) frames lift protection as a tether — a body belt and lanyard attached to the boom or basket, keeping you inside the guarded platform — rather than as fall arrest. The guardrails of the basket are the fall protection; the tether stops you being ejected.

The same conclusion appears in building work at modest heights. Between roughly 6 and 18 feet, a fixed-length shock-absorbing lanyard often has nowhere to work, and the honest answers are a guardrail, a net, a self-retracting device with a documented short arrest distance, or a different way of doing the task. What is not an answer is issuing the harness anyway so that everyone is wearing something.

That is the whole point of this chapter. Clearance is the term that decides whether a compliant system is also a working one, and it is the term you can only settle before the work starts, on paper, with the instructions for the equipment you own.