I have recently been told that steel biners on fixed quickdraws do not dissipate the heat well enough and can cause damage to your rope. If I am not mistaken most climbing gyms around the country use steel biners on their fixed draws. What do you think?
Who told you that, the Tin Man? Steel carabiners are great for high-traffic applications, such as those in a gym and for lowering stations on sport climbs. Steel carabiners are durable, strong and won’t melt your rope any more than aluminum ones.
Certainly, aluminum will dissipate heat more quickly than steel, which has more thermal mass, but denser, heavier steel takes longer to heat up. Because of this, aluminum is used for car radiators and computer heat sinks, while steel is used for expensive skillets.
In our world, the differences are insignificant—carabiners made of either material can theoretically get hot enough to damage a rope. Nylon will start to melt or glaze around 250 degrees F. Tests have shown that a 70-meter rappel, at one meter per second, can heat an aluminum brake bar to 300 degrees. I’ve seen ropes get glazed by a hot, aluminum, rappel device. This was on a hot day, and multiple 165-foot rappels on free-hanging ropes with little cool-down time between rope transfers.
But we’re talking about lowering off a quickdraw, not rappelling, and on a sport route to boot. In this situation, any carabiner, steel or aluminum, will be nearly impossible to heat to the point it will cause rope damage. The distance you’ll lower, especially in a gym, is simply too short. If you’re worried about the top carabiner or anchor getting too hot, insist that your belayer lower you at a sane speed (a great practice, regardless), one that will keep heat build-up to a minimum. And when you fall, don’t mad-dash right back onto the wall. Let your gear (and yourself) chill for a minute. Allowing the rope fibers to cool and regain their elasticity will lower impact forces and add life to your rope much more than trifling with a carabiner.