Copied from an article at Virginia Tech Environmental Health and Safety web page.
The objective of a personal fall arrest system is to not only prevent impact with the lower level, but to minimize the fall forces imposed upon the body in the event of a fall. To understand the basic physics of a fall, take a look at the "Force at Impact" for a 200 pound person at various heights.
|
Elapsed Time |
Distance Traveled |
Velocity (fps) |
Speed (mph) |
Force at Impact |
|
0.00 |
0 |
0 |
0 |
0 |
|
0.25 |
1 foot |
8 |
5.5 |
400 lbs. |
|
0.50 |
4 feet |
16 |
11 |
1,600 lbs. |
|
0.61 |
6 feet |
20 |
14 |
2,400 lbs. |
|
0.75 |
9 feet |
24 |
16 |
3,600 lbs. |
|
1.00 |
16 feet |
32 |
22 |
6,400 lbs. |
|
1.25 |
25 feet |
40 |
27 |
10,000 lbs. |
|
1.50 |
36 feet |
48 |
33 |
14,000 lbs. |
|
1.75 |
49 feet |
56 |
38 |
19,600 lbs. |
OSHA limits the amount of force that a person should experience during a fall to 1,800 pounds. Forces greater than this can result in internal bleeding, damage, or death. When a personal fall arrest system is used, a shock-absorbing lanyard or fall limiter is the only way to keep the fall forces less than 1,800 lbs. Typical force with a shock-absorbing connecting device is 900 pounds or less.
PETZL Article on fall tests and resulting force on climber, belaypoint, and anchor.
Forces at work in a real fall - Petzl USA
Aprox Fall Force calculator
Calculate the force of a fall while using the fall protection force calculator (wilmes.co)