Calculating Free-Fall Distances: HIGHER = BETTER!!!
Use of a connecting device that is designed to arrest a fall requires that the user do some basic calcula- tions before working at height. If the clearance (free, open space) between the user and next lower level is not sufficient, it is possible that a user could still contact a lower level even if the device operates as designed. The type of connecting device used is often dependent upon the amount of clearance availa- ble - and calculations for Energy Absorbing Lanyards differ from those used for a Self-Retracting Device. Energy Absorbing Lanyards Personal fall arrest systems used with this equipment must be rigged to limit the free fall to a maximum of 6’ per ANSI Z359.1-2007. OSHA also requires free falls to be limited to 6’ or less & not to contact lower levels. Fall Clearance:
There must be sufficient clear - ance below the user to arrest a fall before the user strikes the ground or other obstruction. The clearance required is dependent on the following factors: • Elevation of anchorage • Connecting subsystem length • Deceleration distance • Free fall distance • Worker height • Movement of harness attachment element
Anchorage Connector
Free Fall - (6' Max)
Total Fall Distance (Free Fall + Deceleration)
Deceleration Distance
Walking/Working Surface
CALCULATE THE FALL CLEARANCE FOR EAL'S! 1) Determine the lanyard length: Usually 6’
2) Add the maximum shock absorber extension: Limited to 42” (3.5’) by regulations, so [6’ + 3.5’ = 9.5’] 3) Add the height of the anchorage above the user’s feet : If the anchorage is at shoulder height that is about 5’, [6’ + 3.5’ + 5’ = 14.5’] 4) Add a Safety Factor: 1.5’ - 3’ is recommended, depending on system configuration. Consult with a Competent Person to determine the appropriate factor of safety distance for your application. This brings the total clearance needed to 16.5' below the anchorage
Lower Level Obstruction
The 16.5’ figure is the total clearance distance required below the anchorage point, and the distance required below the walking/working surface is 11.5’. For anchorage points that are located below the position of the dorsal D-ring, consider the use of an adjustable-length lanyard to limit free-fall to less than 6’, then re-calculate the fall clearance to ensure that the lanyard can be used safely. The standard adjustable-length lanyard can be adjusted from a 4.3’ to a 6’ length.
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