Strength Soapbox

As the manufacturers push for higher standards to sell more expensive gear to the "infinitely rich" rescue and industrial equipment purchasing agents (many of which can't use the gear they buy), cavers and climbers continue to move toward lighter ropes and smaller ascenders. Who gets the better gear?

I believe that low failure probability is important. I don't know if there has ever been a failure of an 11 mm. climbing or caving rope due to overloading in normal use. All the failures I know of involve cuts or chemicals. Thicker rope wouldn't have helped. Years of practical experience shows that 9 to 11 mm. rope is fine for caving and climbing, and 11 to 13 mm. should be plenty for most light rescue use, if used properly. History has spoken.

Needless to say, I don't take "bigger is better" seriously. If we really need a 3/4" rope because it is stronger, why not use 6-inch ship hawser - or even battleship anchor chain and climb on pelican hooks?

Have you looked up the tensile strength of glass lately? Would you trust a glass descender that held 10000 pounds?

High strength is not the same as low failure probability. They are usually related, but only in an imperfect way. Anyone with basic statistical understanding can easily postulate simple, realistic scenarios where item #1 has a mean breaking strength that is higher (with a standard deviation that is lower) than item 2, yet has still a much higher probability of failure at low loads. Do the math!

Rules of thumb like "the safe working load is 1/10th (or 1/15th) the breaking strength" have no general statistical basis; they may be valid for some things and not for others.

I believe that sometimes there are some arbitrary strength requirements determined by people who couldn't explain a chi-squared distribution if their life depended on it. Most engineers (and even some mathemeticians) cannot explain why a normal distribution is NOT appropriate for predicting failure probability several standard deviations from the mean.

Black Diamond had an excellent editorial in one of their catalog a few years ago. They pointed out how CE certification was preventing manufacturers from selling their highest-quality equipment in Europe. Fortunately, we don't have that nonsense over here (we have lawyers though, that can be worse). I applaud Black Diamond for their efforts to make superior equipment available to those of us who are not impressed by the occasionally ill-conceived industrial and international standards.