How to Correctly Calculate Fall Clearance for Your Fall Protection System

How to Correctly Calculate Fall Clearance for Your Fall Protection System

10th June 2020

When working on a plant platform, boom lift, or any other raised surfaces, falls can occur and your fall arrest system will be useless if it allows you to strike the lower level before stopping you. Therefore, you need to correctly calculate fall clearance for a specific system to prevent possible consequence: injury or death. Fall clearance refers to the minimum vertical distance required between the feet of the worker and a lower level to prevent them from hitting the level in the event of a fall. This lower level can be the ground level or any lower working platform.

Usually, the calculated fall clearance of a particular fall protection system may never be equal or higher than the clearance between the victim’s level and a lower platform. This means that the worker might still hit a solid level when using the fall protection system even when the distance from the working platform to the lower level is lower than the fall clearance of that system.

Please read on to learn more about how you can correctly calculate fall clearance for your system.

Factors to Consider When Calculating Fall Clearance

  1. Free Fall Distance

This is the distance which a worker falls before the fall protection system begins to slow them down. This distance is usually based on the length of the lanyard and the location of the point of attachment. You also need to consider the placement of the anchor point and the activation distance of your fall arrester. For shock-absorbing lanyards:

  • The free fall distance for a system with an anchor point above the attachment point equals:

Lanyard length less the distance between the anchor point and the attachment.

  • For a system with an anchor point below the attachment point, free fall distance equals:

Lanyard length plus the distance between the anchor point and attachment.

  • And for a system with an anchor point that’s level with the attachment point, free fall distance equals the lanyard length.

 

  1. Harness Stretch

Your safety harness will likely stretch in the event of a fall and the attachment point, such as the loop or D-ring, is likely to shift. This variable depends on the elasticity of your harness webbing.

 

  1. Arrest Distance

This is the distance it takes for your personal energy absorber to activate and slow you down. This distance can hardly exceed 3.5 feet in the event of a fall - a typical personal energy absorber usually extends about 2.6 feet.

 

  1. Safety Factor

Safety factor has to be included in the calculation to provide a buffer zone. You’ll need to consider an additional distance before the feet of the worker, about 2.5 feet, to ensure there’s enough clearance between the victim and a lower level.

 

Some of the values above may vary depending on the manufacturer or situation at hand. For instance, horizontal lifelines tend to sag during a fall event and it’s important to consider this sag or else the protection system may be of no use. You’ll also need to consider the length of the user’s body below the D-ring.

You can use the following formula to correctly calculate fall clearance for your personal protection fall system:

Fall Clearance = Free fall distance + Harness stretch + Arrest distance + Safety factor

 

DO NOT proceed to use the system if you do not have the necessary fall clearance to prevent avoidable severe consequences.