A harness and lanyard do not stop a fall at once. They stop it over a distance. If the worker would hit the ground, a beam or a machine before the system has finished doing its job, the equipment is useless. Fall clearance is the free space you need below the anchor point to make sure that never happens.
Enter the figures below, and the calculator will show the clearance needed. If you add the space you have, it will tell you if it is enough.
What is fall clearance?
Fall clearance is the total vertical distance a person will travel from the moment they fall until they come to a full stop, plus a safety margin. It is measured from the anchor point downwards. If there is anything solid within that distance, such as the floor, a lower roof or a pipe, the worker could hit it.
Many people think a harness protects them as long as they are tied off. That is not enough. You also need to know how far the fall will go.
The fall clearance formula
Required clearance = Free fall + Deceleration distance + Harness stretch and D-ring shift + Worker height + Safety margin
It is just five distances added together. All are in metres.
What each part means
- Free fall distance: how far the worker drops before the system starts to slow them down. With a lanyard that is clipped to an anchor at the same level as the D-ring, this is about the length of the lanyard.
- Deceleration distance: the distance the shock absorber stretches out as it slows the fall. This comes from the equipment maker.
- Harness stretch and D-ring shift: the harness stretches and the back D-ring slides up the body as it takes the load, so the worker drops a little further.
- Worker height: the distance from the D-ring on the back to the feet. This is how far the feet sit below the attachment point.
- Safety margin: extra space left as a buffer, because real falls are never exactly like the figures on paper.
Worked example
A worker is using a lanyard with these typical figures:
- Free fall (lanyard length): 1.8 m
- Deceleration distance: 1.07 m
- Harness stretch and D-ring shift: 0.61 m
- Worker height, D-ring to feet: 1.5 m
- Safety margin: 0.9 m
Required clearance = 1.8 + 1.07 + 0.61 + 1.5 + 0.9 = 5.88 m
Now check the space that is actually there. The anchor is on a beam, and the floor below is 5 metres down. Available clearance of 5 m is less than 5.88 m, so it is not enough. The worker could hit the floor.
The team has a few options. They can fit a shorter lanyard, use a self-retracting lifeline that stops a fall in a much shorter distance, move the anchor higher, or use a different system such as work restraint, which stops the worker from reaching the edge at all.
Use real figures, not the typical ones
The example above uses typical values. They are a good guide, but your equipment may be different. Always take the free fall, deceleration and stretch figures from the maker’s instructions for your harness, lanyard and anchor. If a number is missing, do not guess. Ask the supplier.
Where you put the anchor makes a big difference
- Anchor above the shoulders: keeps the free fall short and gives the lowest clearance requirement
- Anchor at foot level: the worker can fall much further before the system catches them, so you will need a lot more clearance, and the equipment must be rated for it
- Anchor off to the side: a fall can swing the worker sideways into a wall or a machine, which is called a swing fall
Step by step
- Find the position of the anchor and the nearest obstacle below it.
- Take the equipment figures from the maker’s instructions.
- Enter free fall, deceleration, stretch and worker height, and set a margin.
- Read the required clearance.
- Enter the available clearance if you know it.
- If the space is not enough, change the system or the anchor point.
Other things a fall arrest plan needs
- A strong anchor: it must meet the strength your standard asks for, and it should be chosen by a competent person
- A rescue plan: a person hanging in a harness can suffer serious harm in minutes, so you must be able to get them down quickly
- Inspected equipment: check harnesses, lanyards and connectors before each use, and have them checked by a competent person on a schedule
- Trained workers: people must know how to fit the harness, connect it and what to do after a fall
- The right system: if you can prevent access to the edge with a guard rail or restraint, that is better than catching a fall
Common mistakes
- Forgetting the worker’s height, which is easy to miss
- Using typical figures when the equipment label says something else
- Measuring the clearance from the ground to the worker’s feet and not from the anchor
- Skipping the safety margin
- Tying off low, and then having too little space
- Having no plan to rescue a person after a fall
- Using a lanyard that has already been used in a fall
Linking it to your wider plan
Preventing a fall is always better than arresting one. Start with the risk matrix calculator to score the work at height, and use the residual risk calculator to show how much safer the task is after you add controls. If your team uses leaning ladders, check the ladder angle calculator for the correct setup.
Frequently asked questions
What is fall clearance?
It is the free space needed below the anchor point so that a falling worker is stopped before hitting anything below.
How much clearance does a typical lanyard need?
With typical figures it is around 5 to 6 metres. Your own equipment may differ, so always check the maker’s instructions.
Why is worker height included?
Because the anchor is on the back D-ring. The feet hang about 1.5 metres lower, and they are the part that could hit the ground first.
What if I do not have enough clearance?
Change the system. Use a shorter lanyard, a self-retracting lifeline, a higher anchor, or a restraint system.
Is fall arrest the first choice for work at height?
No. Avoid work at height if you can, then use guard rails or other edge protection. Fall arrest is a later step.
Learn this properly
Work at height and fall protection are covered in NEBOSH, IOSH and OSHA courses. ISH Institutes teaches these in Peshawar. Chat with us on WhatsApp and we will help you pick the right course.