Over nearly 30 years of scouting, the rules got nuttier and nuttier. I'm an expert in vertical rope work: rappelling, ascending rope, high angle and vertical rescue. So the scouts decide, against the recommendations of the cavers and climbers they asked to help write BSA rappelling rules, to require a second rope to be attached to each boy who is rappelling. There is no doubt in our collective minds that the insurance companies and lawyers insisted on this. The second rope is handled by a "belayer", a person who is supposed to stop the rappeller from falling. There's only a few problems with this. One, you can't see the kid that's on rope. Two, one of the most common issues with beginners is feet slipping out from under them. When that happens, the person on rope can twirl a bit. Guess what? Now the two ropes are twisted. This guy isn't going anywhere like down. You sure can't haul them back up. And of course, the kid is scared, and generally not able to help themselves. The second rope just compounded a very minor problem. The only solution is to have another rope rigged for rappel beside the main rope, and you send an experienced person down on this rope to unwind the mess.
OK, you say, but a second rope seems like a good idea! What if the rope breaks? What if (and if you know rappelling, you know this is another common mistake) the rappeller lets go of the rope - now they have no control. First issue I have is this. I've been doing vertical work since I was 14 years old. I've climbed and rappelled thousands of feet with many, many different people. We use 7/16" (11mm) kernmantle rope (special rope designed for climbing and rappelling). I've read every issue of American Caving Accidents. This is an annual publication detailing every accident in the caving world that can be documented, even if only through news or anecdotal reports. Guess how many times a broken rope has figured in an on-rope accident? None that I can find. Zero. The ropes are very strong. People take care of them. Regular inspection reveals flaws that cause ropes to be retired and turned into short pieces used to teach knot tying. Here's the answer to the second issue. Bottom belay. A person on the bottom of the drop who has the rope wrapped behind their thighs. Rappeler lets go of the rope, belayer puts some downward tension on the rope. A hundred and ten pounder can stop an adult. It's that simple.They don't stand directly under the rappeller. They wear protective gear. And they pay attention to the person on rope. It works.
There is no foolproof way to totally protect someone rappelling, but when you go 35 years doing it and teaching it, and no one in your charge has done anything worse than a pair of wet pants and a slightly sprained ankle, that's not chance, that's adherence to the rules that matter, not the artificial ones. Anyone who doesn't will pay the price, and even useless rules won't be useful!