Fall Clearance: How to Correctly Calculate


If you or your construction team work at heights, you must understand how to effectively calculate fall clearance. This is the distance needed to prevent a worker from hitting the ground or lower level in case of a fall.  Because even a small miscalculation can result in serious injury or death, accuracy is essential.

Follow these guidelines to effectively calculate fall clearance.



Consider the Length of the Lanyard and Deceleration Device

Include the deceleration device and harness to determine how long the lanyard needs to be when working at a specific height. For instance, because deploying the deceleration device adds 3.5’ to the length of the lanyard, the 3.5’ must be added to the lanyard length. Also, keep in mind that the harness can stretch so that the anchor point ends up a foot or more above the worker’s head after a fall. This is why a worker at a height of 10’ should use a lanyard of 10.5’.

Add in the Length of the Worker’s Body

Take into account the length of the worker’s body below the D-ring. In most cases, you can safely consider it 5’. However, people of different heights may need other considerations to ensure their PFAS is effective.

Include the Length of Anchorage Point Connector  

If the worker is using a fixed anchor point, the only distance you need to add is the length of your snap hook. However, if the worker is using an anchor such as a horizontal lifeline, you must account for sag. To figure out the sag in design, you could pull the lifeline tight to determine the distance. Or, to find the sag from a fall, you may estimate anywhere from 3% of the total length of a high-tension line to 15% of the length of a line that uses shock absorbers.  Keep in mind that the longer the span, the more sag there will be. You may want to shorten your spans and use double lanyards to attain complete fall protection.

Figure in the Safety Factor

Build in a safety factor in case things do not go exactly as calculated. An additional 3’ should be effective. Always err on the side of caution.

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