To ensure the safety of workers at height, it is essential that fall arrest systems are correctly set up with enough clearance to stop a fall safely without the user making contact with the ground or other obstacles. The required clearance varies depending on the type of fall arrest equipment in use, and calculations must take into account several factors.
Key elements to consider:
The height of the user, which is generally taken as 2 metres from the connection point to the feet, to allow for the user’s actual height and potential harness stretch.
A minimum safety clearance of 1 metre must always be included.
The type of equipment being used—fall arrest lanyards and self-retractable lifelines (SRLs) require different calculations.
The position of the anchor point, which affects the potential fall distance and fall factor.
Fall arrest lanyards
To calculate the required clearance when using a fall arrest lanyard:
A = Length of the lanyard under tension
B = Length of the deployed shock absorber (if applicable)
C = 2 metres to allow for the distance between the anchor point and user’s feet after a fall
D = 1 metre recommended safety clearance
Formula:
Clearance required = A + B + 2m (C) + 1m (D)
Self-retractable lifelines (SRLs)
SRLs operate similarly to a car seatbelt, locking off quickly—typically within 400mm—to minimise the fall distance. These are particularly useful in workspaces with restricted height where a full-length lanyard cannot be used safely.
When calculating clearance for SRLs, you must add:
- Free fall distance (up to 400mm before braking begins)
- Braking distance during deceleration
- Harness stretch and user height (assumed 2 metres)
- 1 metre safety clearance
If the SRL includes an integrated shock absorber, the deployed length of this absorber must also be included in the clearance calculation.
Key points:
- Always include 2m for user height and harness stretch, and an additional 1m for safety.
- For lanyards: clearance = device length + shock absorber length + 2m + 1m.
- For SRLs: consider free fall, braking distance, harness stretch, and safety clearance.
- SRLs can be more suitable where available fall clearance is limited.
- Anchor point height and location influence fall distance and must be considered.
If you need further support, please contact our Technical Support Team using the email: technical@jspsafety.com or contact us via WhatsApp.