KiloNewtons to Pounds
Jeff's Question:
I climb frequently, but for some reason I can't find the kiloNewton-to-pound conversion. I am debating this with my friends, but we can't seem to find a good resource.
Thanks,
— Jeff
Don's Answer:
Jeff,
As an American, liberal arts major, I wish the manufacturers would go back to old-fashioned pounds—all this physics and metric stuff has me confused too.
Plus, I still go by the adage that gear doesn't break: it pulls out, comes untied, or unbuckled. Human error is a much more significant issue than the strength of this or that piece of gear. If you doubt this, read a few annual issues of Accidents in North American Mountaineering, collected and published by the American Alpine Club. You won't find too many accidents resulting from"failure of equipment." Most are attributed to "failure of judgment."
One kiloNewton (kN) is the force required to change the inertia of a mass of a little over 220 pounds. Simplified, a piece of gear rated to one kN will hold 220 pounds. A carabiner rated to 24 kN will hold about 5,000 pounds.
A good way to think about the strength required in a climbing system is to consider the UIAA drop test for a rope. (The Petzl catalogue is superb in its description of forces in climbing. See it at www.petzl.com). If the worst-case impact force in this unrealistically brutal test is around 2,000 pounds, and if the fall creates a pulley effect on the high carabiner (as in a leader fall), then that point gets about 4,000 pounds. In reality, we can't duplicate this in the field because our system is softened by rope slippage, soft climbers, and belayers yanked upwards. All of these factors reduce the forces. Moreover, a true pulley isn't possible on a carbiner. The friction here reduces it by at least a third.
Based on this oversimplified layman's model, the only kind this liberal arts brain can grasp, 4,000 pounds (excuse me, 18 kN) is considered absolutely strong—what climbers call "bombproof."
Still, remember that there's less impact when the belay is "soft" and when there's a lot of rope in the system.
Hope this helps,
—Don
from Away.com
