If you have workers at height, making proper use of a fall arrest system is crucial. It can mean the difference between life and death.
The commonly used self-retracting lanyard (SRL) contains a drum-wound line that slowly extracts or retracts. It extends when the worker moves around and maintains enough tension to make sure the line is never slack. If a worker falls, the rapid extraction of the line automatically locks the drum (like your car's seat belt does when you pull it too quickly). It then keeps the user from falling any further.
While SRL manufacturer manuals list the maximum arrest distance for the device, the leading edge (LE) arrest distance is usually expressed the same as all other SRLs in the series and doesn't factor in the additional fall distance, swing-fall distance, maximum payout of the shock pack, or additional rotation of the rotary brake.
If you want to figure out the full payout of the fall arrest components, you'll need to request that information from the manufacturer. We recommend that you request it in writing from the engineer, if possible.
Once you've gathered that information, you can calculate the arrest distance with this equation:
x = (ffmax x w) / (Favg – w)
Where:
x = Total payout of the arrest system in feet
ffmax
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distance in feet (note that the height of the wearer will affect the free fall distance when tied off below the dorsal D-ring)
As you can see, calculating the arrest distance involves many variables. And this formula doesn't even factor in environmental conditions like temperature and moisture. Each situation is different, so it's best to take a conservative approach when calculating the clearance you need to safely use an SRL-LE. When you're in doubt or need clarification, don't be afraid to call the manufacturer.
One final word. Since safety is the name of the game, you might want to consider using multiple safety systems. For example, a horizontal lifeline (a cable attached to two or more anchor points on an elevated work area) can be used in combination with other fall protection PPE. This limits the amount of force transferred to both the worker and the fall arrest system.