3M DBI-SALA 1246518 User Manual page 10

CALCULATING CLEARANCE (EXACT VALUES)
There are two common methods for calculating clearance requirements. The "Working Surface Method" finds Required Fall
Clearance (FC), which is measured from your working platform to the next obstruction below. The "Anchorage Method" finds Total
Fall Distance (TFD), which is measured from one's anchorage point down. Both methods are acceptable for finding your clearance
requirement. Select whichever method you are more comfortable with.
WORKING SURFACE METHOD
1. Find your Free Fall (FF). See "Measuring Free Fall".
2. Find your Deceleration Distance (DD). See "Energy
Absorber Tables".
3. Add it up to get Required Fall Clearance (FC):
• Free Fall (FF)
• Deceleration Distance (DD)
• Harness Stretch (HS): 1.5 ft. (0.45 m)
• Safety Factor (SF): Minimum of 1.5 ft. (0.45 m).
• If you did not measure Free Fall while standing: If
crouching, add 3 ft. (0.91 m). If lying prone, add 6 ft.
(1.52 m) instead.
FF
DD
DD
HS
SF
MEASURING FREE FALL
You must never exceed the Maximum Free Fall for your lanyard. See Figure 2
for the Maximum Free Fall for your lanyard. To ensure you are not exceeding
this limit, you must determine the amount of Free Fall (FF) in your system.
;
Free Fall (FF) must be measured from a standing position. Crouching or
lying prone reduces effective user height.
1. Find Free Fall (FF). Free Fall (FF) varies with where your anchorage point
is located. Select the option that applies to your situation.
Anchorage How to Find
Point Location Free Fall
Above D-ring Subtract DP
from LL
Below D-ring Add DP to LL
FF
DD
HS
FC
Legend:
DP = Distance to Anchorage Point
LL = Lanyard Length
ANCHORAGE METHOD
1. Find your Lanyard Length (LL). See Figure 1.
2. Find your D-ring Height (DH). This is the height of your
D-ring above the working surface. This is typically 5 ft.
(1.52 m) for a user who is 6 ft. (1.83 m) tall.
3. Find your Deceleration Distance (DD). See "Energy
Absorber Tables".
4. Add it up to get Total Fall Distance (TFD):
• Lanyard Length (LL)
• D-ring Height (DH)
• Deceleration Distance (DD)
• Harness Stretch (HS): 1.5 ft. (0.45 m)
• Safety Factor (SF): Minimum of 1.5 ft. (0.45 m).
5. Confirm your Free Fall (FF) does not exceed the limit
for your lanyard. See "Measuring Free Fall".
DH
LL
DD
DD
HS
SF
DP
LL
FF
FF = LL - DP
10
LL
DD
HS
TFD
DH
DP
FF
LL
FF = LL + DP