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3.5
SELECTING A CLEARANCE CHART: Users should begin by selecting their connecting subsystem type. The user should
then follow the instructions specific to that connecting subsystem to determine what fall clearance chart to use.
;
All Required Fall Clearance values in these instructions include a safety factor of 2 ft. (0.6 m) plus an additional
10-percent of HLL deflection. 1 ft. (0.3 m) of additional fall clearance is included for harness stretch and D-ring slide.
;
All Required Fall Clearance values in these instructions were calculated using the maximum free fall distances stated
in Table 1. Greater free fall distances will require more fall clearance.
;
When using connecting subsystems made by a different manufacturer, 1 ft. (0.3 m) of additional fall clearance must
be added to the values in the fall clearance charts to account for unknown variation in product performance.
3.6
FALL CLEARANCE FOR ENERGY-ABSORBING LANYARDS: Fall clearance is the measure of distance between a user
and the next obstruction below them. Required Fall Clearance (FC) is the amount of fall clearance needed to safely arrest
the user during a fall event. Fall clearance is always measured from the top of the working platform to the top of the next
obstruction below. To determine Required Fall Clearance for energy-absorbing lanyards, refer to the following sections:
A. FREE FALL DISTANCE: The user should determine how much free fall is present in their system before using the fall
clearance charts. Lanyard length and system placement (anchorage height, setback distance) are the primary factors
affecting free fall distance. When a lanyard is anchored below the user's D-ring, free fall distance will exceed lanyard
length, up to as much as twice the lanyard length.
Figure 7 illustrates the amount of free fall associated with common system applications. However, the user must still
verify the amount of free fall present in their intended application.
Free fall is measured from the top of the user's D-ring before a fall to the top of that same D-ring when the lanyard
tightens during a fall. 3M Fall Protection shares the following method for measuring free fall in a system:
Measuring free fall distance for an HLL:
1.
Connect one end of the lanyard to the HLL. Extend the free end toward the edge of the working platform and let
it hang over the fall hazard.
2.
Measure how far the hook on the free end hangs below the working platform.
3.
Add the initial height of the worker's D-ring above the working platform to the measurement from Step 2. The
sum of these two numbers is the free fall distance for your application.
B. FALL CLEARANCE CHARTS: See Figure 8 for reference. Required Fall Clearance (FC) is determined by Maximum
Free Fall (FF) of the system application, HLL System Span (B), and the number of users connected to the HLL System.
To determine Required Fall Clearance (FC) using Figure 8 for Energy-Absorbing Lanyards:
1.
Identify the amount of free fall distance that could occur given the specific anchorage height, setback distance,
and lanyard used in your application. Select the chart that meets or exceeds your Free Fall Distance (FF). It is
recommended that free fall distance be kept to a minimum.
2.
Select the table column that matches your number of users. Ensure the combined weight of each user
(including clothing, tools, etc.) does not exceed the maximum capacity listed.
3.
Find the row in the column to the far left that matches your System Span (B).
4.
Find the corresponding Required Fall Clearance (FC) where the column for your number of users and the row for
your System Span (B) intersect.
6.0 ft.
FF =
(1.83 m)
Figure 7 - Free Fall in HLL Systems
6.0 ft.
FF =
FF =
(1.83 m)
6.0 ft.
FF =
(1.83 m)
(2.44 m)
8
8.0 ft.
12.0 ft.
FF =
(3.66 m)
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