Cold shuts are cheap. Available. And relatively easy to modify into bolt hangers - simply bend the eye over, slap on a weld, and you're in business. It's no wonder, then, that
cold shuts are popular replacements for regular bolt hangers, especially on sport climbs, where they let you thread the rope and lower from any point on the climb.
But are these hardware store variety links, designed to repair or join chains, safe for climbing? None of us would climb on a rope that our buddy wove in his garage, but man' of us trust
cold shuts implicitly. After all, we've fallen on the things and they've held. While this observation may satisfy some people, most of us have questions about cold shuts lurking in the back
of our minds.
To resolve the issue, Will Manion, a civil engineer at the University of Maine, and I pull tested 70 cold shuts, both old and new, including 55 3/8 inch and 15 1/2 inch jobs. Here are our
How much should protection hold? Before we get into the nuts and bolts of the testing, let's look at the strength and safety margin that should be built into our gear. For a 176 pound leader
in a hard (factor 1 or higher) fall, the loads simulated in drop tests and verified mathematically are 1200 to 1600 pounds. While those numbers might seem low, you must remember that the protection
will be subjected to an equal counterweight force from his belayer. So, the load on your protection can range from 2400 to 3200 pounds or more.
Using 3200 pounds as the baseline, it is standard-to account for variables such as manufacturing and material defects-to factor in a safety margin of at least two. (For comparison, most bolt
companies use a safety factor of four for their products.) That done, we arrive at 6400 pounds, which is in fact close to the average strength of most commercial bolt hangers.
Are cold shuts reliable? Since all coldshut hangers are homemade, their strengths vary with the metalbending and welding skills of their creator. Coldshut strength also depends on the metal
and manufacturing quality. A glance through the hardware store bins will tell you that coldshut manufacturers have slim, if any, quality assurance programs. Some cold shuts are bent haphazardly;
others have the eye hole off to the side, so the eye is thick in one spot and thin in another. These manufacturing variations are hardly reassuring, and can only make you wonder how the metal
gets treated at some overseas manufacturing plant.
For our tests we used 3/8 and 1/2inch non-heat-treated cold shuts, the type most commonly used for bolt hangers. Heat-treated cold shuts are stronger, harder (they withstand rope wear better),
and generally better made. But, heat-treated cold shuts can cost as much as regular bolt hangers and are difficult to find, negating much, if not all, of their perceived advantages.
We pull-tested the cold shuts in three directions: straight down (0 degrees) to simulate the load on a vertical wall; straight out (90 degrees) for a horizontal ceiling; and in between (45
degrees) for a severely overhanging wall. The cold shuts pulled straight down were the strongest. Indeed, the steeper the wall, the weaker the cold shut, probably because these steeper angles
transmit more of the load directly onto a coldshuts Achilles' Heel, the weld.
Our tests confirmed most fears. The welded 3/8inch cold shuts we scavenged off crags broke at loads as low as 2120 pounds and as high as 8180 pounds. New 3/8inch cold shuts made specifically
for the test were stronger overall, but still inconsistent, holding between 4360 and 7280 pounds. The 1/2inch cold shuts were far stronger, holding between 8550 and 12,550 pounds.
Most cold shuts broke at the weld. The good news is that when most cold shuts failed, they "unwound" gradually, rather than suddenly exploding. Once the weld had cracked, most 3/8inch
cold shuts held around 800 pounds, and most 1 /2inch shuts held 2000 pounds before completely straightening. The bad news is that several cold shuts suffered catastrophic failures, breaking
in two at their "necks," proving again the unreliable nature of these jury-rigged hangers.
To an engineer, handmade welded cold shuts are unacceptable as bolt hangers because they fail a crucial criteria for safety: consistent breaking strengths. The 74% strength variances for
3/8inch cold shuts are horrific. Half inch cold shuts, which have a larger weld, didn't vary quite as much, but they still revealed an unacceptably high 32% variation between the weakest and
To a climber, cold shuts would still seem relatively safe: after all, even the weakest of the test batch held over a ton. Not so fast. To get a clear picture of whether we should trust cold
shuts we need simply to apply their random breaking patterns to other pieces of gear. Take, for example, a carabiner with a rated strength of 5000 pounds. Apply the 3/8inch cold shuts 74percent
strength variation to this carabiner and you now have a piece of equipment that can break anywhere between 1300 and 5000 pounds. Apply the 1/2inch cold shuts 32percent variation and the carabiner
can break between 3400 and 5000 pounds Factor in that carabiners can twist on a cold shut and unclip themselves, and you can only draw one conclusion - cold shuts may be cheap, but they aren't
worth the risk.
Reprinted from Climbing Magazine