Fall Protection Clearance calculator — how far you need underneath you Teaching tool
British Columbia Module 06 · Forces & clearance Practical item P1

How far do you need underneath you?

A harness only saves you if there is room to stop. Set your anchor, your lanyard and your gear below and watch the fall stack up in 3D — free fall, absorber deployment, harness stretch, safety margin — against the clearance you actually have. Every number names the rule it comes from.

2 mMax free fall with an energy absorber — G11.5-3
1.2 mMax free fall, synthetic lanyard, no absorber — G11.5-3
8 kNBC ceiling on maximum arrest force — G11.6-1
22 kNTemporary fall-arrest anchor, or 2× MAF — OHSR 11.6
Drag to rotate · pinch to zoom

Motion is illustrative — the figures are the static clearance values your gear's labels govern.

GO Required 3.85 m · Available 4.50 m · 0.65 m spare
The clearance chain Z259.16 structure
Total clearance required12.6 ft 3.85 m
You have4.50 m
Spare0.65 m
1 · Your setup
+1.00 m above

Where the anchor sits compared with the D-ring between your shoulder blades.

An anchor below your D-ring makes the free fall longer, not shorter

1.80 m
Energy absorberYes

G11.5-3 — no absorber on a synthetic lanyard caps free fall at 1.2 m

1.75 m

From the absorber's label — check yours

2.00 m

G11.5-3 — 2 m, or the manufacturer's limit when it is lower

2 · You and your harness
1.50 m

Where your dorsal D-ring stands above the surface. Changes the picture, not the sum — the reason is below.

0.30 m

From the harness instructions — the manufacturer's figure governs

1.00 m

ATF house rule — some manufacturers specify more

3 · Where you're working
4.50 m

Measure it. Surface you stand on, down to the first thing you could hit.

Sloped roof over 4:12No

G11.2-1 — over 4:12 you slide before you leave the edge

2.00 m

Added to the chain — G11.2-1

How it is worked out

Four lengths, measured from your boots.

Everything is measured down from the surface you are standing on, in that order. That is the same way it is done on the scenario card you are handed at the practical assessment.

  1. 01Free fall

    How far you drop before the system starts stopping you: lanyard length, minus however far the anchor sits above your dorsal D-ring. Anchor below the D-ring? Subtracting a negative makes the free fall longer.

    G11.5-3 — 2 m with an absorber, 1.2 m without

  2. 02Deceleration

    How far the energy absorber pays out while it brings you to a stop. Read the number off its label — never off memory. No absorber means nothing pays out, and the arrest force lands on you instead.

    Manufacturer's label governs

  3. 03Harness stretch and D-ring shift

    The webbing gives a little and the D-ring rides up your back. The harness instructions state the figure.

    Manufacturer's instructions govern

  4. 04Safety margin

    What is left between your boots and the deck below when everything has stopped moving. A margin is required; the metre used here is our own house figure, and some manufacturers call for more.

    ATF house rule — labelled, not law

Why your height is not in the sum

The length of your body hanging below the D-ring is about the same as the height of that D-ring above the surface, so the two cancel out. That is why the chain is measured from the walking surface, and why changing the figure's height in the scene moves the picture without moving the answer.

Working off to one side? Add swing.

This tool assumes you are directly below your anchor. Step sideways and a fall becomes a swing: you travel further, you can strike the wall, the structure or the ground on the way, and the clearance you need grows. The fix is to move the anchor over the work, not to recalculate.

G11.5-2 · G11.6-2 — minimize swing fall

Force is the other half of the story

This tool works in distances. Force is what the absorber is for: BC caps the maximum arrest force at 8 kN, and an anchor rated under 22 kN needs an absorbing system unless an engineer says otherwise. A temporary fall-arrest anchor is 22 kN, or twice the maximum arrest force.

G11.6-1 · OHSR 11.6

Read this before you use a number

What this tool is not.

Standing note

This is a teaching tool. Your equipment's labels and instructions govern. Your employer's site-specific plan governs.

The free-fall limits and the arrest-force ceiling come from the BC OHS Guidelines and are named on screen. Deployment and stretch come off your own gear — the defaults here are example figures, not specifications. The safety margin is an ATF house rule: a margin is required, the exact metre is ours and it is labelled that way everywhere it appears.

Some setups have no correct number at all. A device used outside its instructions — a plain self-retracting lifeline anchored at your feet, for instance — cannot be made acceptable by arithmetic. The right answer there is to stop and ask for different gear.

WorkSafeBC does not approve or certify fall protection courses or tools. Under Guideline G11.2(6)-1, no course on its own is enough: your employer must also give you site-specific instruction before you enter an area with a fall risk.