The following article is courtesy of Black Diamond Equipment.
Carabiners are incredibly strong—they meet a minimum
test of 20 kN (4496 lbf or 2039 kg) when properly loaded on their major axis with the gate closed. In an open gate scenario, carabiners still test
to a minimum of 7 kN (1574 lbf or 714 kg).
But when you test a nose-hooked carabiner, it can fail at less than 10% of its rated closed gate strength—that's less than 2 kN (500 lbf or 227 kg),
a load that can be easily generated in even the smallest of climbing falls or even just a light bounce test.
Why is the carabiner's breaking strength so low when loaded in this manner? It's a combination of an open gate scenario coupled with the fact that the
carabiner basket is being cantilevered off of the bolt hanger/sling/Stopper wire, meaning the load is not in line with major axis (i.e., the carabiner's
spine). This off-axis loading causes the carabiner to be excessively torqued and break at an extremely low load.
Black Diamond manufactures a lot of carabiners, and therefore Black Diamond tests a lot of carabiners. We not only understand the loads at which carabiners
break, but also the modes (i.e., location of breakages), depending on the way it was loaded. So it's possible to look at where a carabiner is broken
and have a good idea of how it was loaded.
The photos below show typical failure locations for one style of carabiner tested in four different configurations. As you can see, a nose-hooked carabiner
will most often break at the top of the spine, while open and closed gate failures typically occur at the bottom of the spine, and minor axis failures
almost always occur at the gate.
[Disclaimer: All carabiners are different, and detailed analysis of the particular carabiner's geometry and failure modes is necessary in order to be able to estimate the particular loading scenario with any level of confidence.]
When a carabiner is loaded while the nose is hung-up on a bolt hanger, a leveraging open-gate scenario occurs. Carabiners are significantly weaker in this
configuration—less than 10% of closed-gate strength.
How to avoid this? Always ensure that the carabiner's gate is closed and the carabiner is correctly seated.
Climb safe -
Kolin Powick (KP) is a mechanical engineer hailing from Calgary, Canada. He has over 20 years of experience in the engineering field and served as Black Diamond’s Director of Quality for over 11 years. He is currently their Climbing Category Director. If you have a technical question for KP, please email him at firstname.lastname@example.org and he will TRY to respond.
To help make more climbers safer climbers, Rock and Ice has teamed up with Black Diamond Equipment to present the information here.