What is Total Fall Distance?
Total Fall Distance = Free Fall Distance + Maximum Shock Absorber Extension + Harness Effects + Height of Person + Safety Factor
Knowing total fall distance is vital to any height safety risk management plan. The total fall distance provides insight into what fall protection equipment is appropriate for each job. In fact, knowing total fall distance is just as important as having the proper equipment.
Free Fall Distance = Length of Lanyard – (Distance Between Anchor Point and Working Surface + Distance Between Worker’s Lanyard Attachment and Working Surface)
Free Fall Distance
Free fall distance is the amount of vertical free fall experienced by the worker between the initial start of the fall and the point where the shock absorbing system kicks in. Free fall distance equals the length of the lanyard, minus the straight line distance between the anchor point and working surface, plus the distance between the worker’s lanyard attachment point and the working surface. As per Australian regulations, free fall distance must not exceed 2m.
TIP: To decrease free fall distance always keep the anchor point as far above the attachment point on the harness as possible.
Maximum Shock Absorber Extension
The maximum shock absorber extension is the vertical distance traveled between when the shock absorbing mechanism is activated and the final arrest. Check each individual shock absorber for this distance. For shock absorbing lanyards the maximum extension permitted is 1.75m. A self-retracting device has a maximum extension of 0.7m.
The harness effects takes into account the stretch of the harness during an arrest. In most circumstances this can be estimated to be approximately 0.3m.
Height of Person
You need to be aware of the workers’ height to approximate clearance distance. The height of person is the total height of the worker, minus the distance between the top of the worker’s head and the lanyard attachment.
To ensure that there is adequate clearance between the worker and the below working surface, always include a safety factor to your total fall distance. It is recommended that your safety factor allow for at least 1m. Once the total fall distance has been calculated, it must be ensured that this fall distance is less than the distance between the working surface and the next closest object in the fall path.