A crucial tool to ensure safety when working at height is the personal fall arrest system (PFAS), a multi-component system that stops a worker mid-fall and prevents them from impacting with a surface. A worker, secured in a full-body harness, is tied to an anchorage point via an anchorage connector and a shock-absorbing lanyard or self-retracting lifeline which will arrest a fall. A fall has multiple potential sources of impact, though, and while this system saves lives, it also requires precise calculations to prevent the worker from hitting those points of impact. And even when shock-absorbing lanyards and deceleration devices are being used, they must ensure that the force of stopping the fall won’t injure the worker. This is where fall clearance calculations come in.

The minimum vertical distance required to ensure a worker doesn’t contact a lower level during a fall is the total fall clearance distance. Calculating this requires numerous factors, and when you add these numbers together, you’ll find the minimum clearance distance.

• Free fall distance: the fall distance before the PFAS begins to slow the fall, which must be 6 feet or less to prevent contact. It also depends on two other factors, which will contribute to its own calculation (Free fall distance = Lanyard length +/- the distance from the D-ring to the anchor. Add that distance if it’s above the anchor and subtract if it’s below).

          o Lanyard length

          o The height at which the lanyard is anchored relative to where the other end attaches to the worker’s harness

• Deceleration distance: The distance the worker will travel while the deceleration device is slowing the fall and absorbing its energy
• Back D-ring height: this is often standardized as 5 feet, but for workers over 6 feet tall, adjustments must be made
• D-ring shift: the distance the D-ring moves and the harness shifts while supporting a worker’s full weight; a back D-ring’s height can change 1 foot or more!
• Safety factor: an additional distance, typically 2 feet, added to the total clearance distance to ensure clearance

Another factor in fall clearance is the swing fall hazard. While it’s ideal to have an anchor directly overhead, it’s not always feasible in your workspace. When anchors aren’t directly overhead, a worker whose fall is arrested will swing back and forth like a pendulum. A PFAS set up in the wrong place can mean swinging into beams, walls, or other objects, potentially leading to serious injury.

These are challenging considerations that involve many data points that need to be accurately compiled and calculated, as well as your own evaluation of the workspace and the safest, most secure place to set up a fall arrest system. You can ensure safe clearance, however, with the right fall distance calculator. When using FallTech™ SRLs, you should consider the AXIS® Fall Clearance Calculator. It’s free to register and use, and ensures correct calculations.

1. Precision accuracy to the inch across multiple calculation formats
2. Equipment compatibility with a range of FallTech SRLs, meaning accurate product data on factors like lanyard length and deceleration distance
3. Detailed PDF reporting featuring clearance specifications, visual illustrations, and timestamps
4. Full 3D modeling of your data, including clearance and safe zones

That last feature can be vital. By providing a full 3D representation of the working space, fall arrest system, worker, and all relevant distances, the AXIS Fall Clearance Calculator gives you visibility into safe clearance zones that calculations and even viewing the worksite can’t offer. That visibility can make for crucial understanding about where and how to set up your PFAS to ensure proper safety in a fall.