Nerve damage is a common problem, but one which is rarely discussed in any detail in most tutorials. Nerve damage can be painless and thus occur without warning; it can also happen in seconds. At worst it can be permanent, although fortunately most bondage injuries recover without any treatment in two to twelve weeks.
Unfortunately individuals are as different inside as they are outside, and vary in their susceptibility, so the following is at best a general guide and certainly no guarantee of safety.
The first method of minimising damage is to stick to the rule of being able to stick at least one finger easily under the rope, since damage is usually caused by excessive pressure. Always be aware how things can change. Pressure from lying on a rope; the effect of a load; or tightness due to a different position, can mean that what was safe a moment ago is no longer.
The second is to learn which are the vulnerable areas, and most importantly, know your partner's body. You can get a good idea of locations, vulnerabilities and sensitivities by gently probing some of the areas that I'll describe. Some will produce a pronounced twinge when you hit the nerve. Familiarity with the sensation is helpful in learning the warning signs of pressure on a nerve.
Starting with the hands, the first area to watch out for is here, in the notch between the hand and arm bones. On the thumb side, you have the radial nerve servicing this part of the hand; on the other you have the ulna, serving this part. Some people, especially if they carpal tunnel build-up, might be sensitive to pressure on the median, here.
Moving up, we have another point that is about three fingers above the point of the elbow. On the inside, where the ulna becomes exposed, about here.
Next we have a relatively unprotected area in the valley between these two muscles, where the radial runs. You might remember that from school, which is where a 'dead arm' is applied.
IMPORTANT NOTE: The radial is generally lower but the advice on placement is generally safer than tying too low. See accompanying notes.
Finally, there is a very sensitive are on the inside of the upper arm. The lower part is the radial again, and more into the armpit area is a big junction of nerves called the brachial plexus.
The main area to watch out for here, is along the knicker line, where the femoral nerve and artery lie.
Avoid pressure on all these points. However sometimes this in itself is not enough, and certain individuals can find nerves trap simply due to a position which doesn't suit their body. For example, some people find cross legged positions cause a problem, especially with their body bent forward. Others find this position might cause entrapment in the shoulder area.
This thing to remember is that we're all different and have varying susceptibilities. It's important to be very aware of any tingling, odd twinges, unpleasant pain, or loss of sensation and ask the rigger to take remedial action. It's always better to be safe than sorry. The most common words after a nerve incident are "it didn't feel right at the time, but I was having such a good time...”. Don't be the next person to say that!