Physics of a Fall
The Relationship of the Fall to the Impact
Examining fall distances and impact forces is a worthwhile exercise for any “at-height” operation. In the occupational safety realm the implication of workplace falls above 4 feet becomes quite clear when viewing the figures below. This is in part why States such as Washington have moved away from the federally mandated 6 foot trigger height for fall protection to a more conservative 4 feet.
When looking at impact forces through the lens of rope access or rescue we can substitute the concept of a falling worker with that of a dynamic event resulting from a failure within our rope system. With more than 1 person in the system the impact forces will naturally compound to both the individual(s) and to the anchor.
Its helpful to remember:
With a 6 foot lanyard tied off even with your D-ring you will free-fall 6 feet (the maximum allowable fall distance per OSHA) before your Personal Fall Arrest System (PFAS) engages.
For every 1 foot below your D-ring that your lanyard is tied off you will free-fall 2 additional feet before PFAS engages. OR, for every 1 foot above your D-ring that you tie off you will free fall 2 feet less.