Cookie said:
Hi Bob,
interesting stuff but could you make it clear that at this stage this is unofficial advice from Bob Mehew and not approved advice from the BCA. Obviously that might change in the future once it has gone past the E&T Committee.
For my part I agree with your second sentence about retying after a fall but am concerned about the first.
I can see in isolation it make sense but what about the unintended consequences? There are no studies into the increased risk of knots untying themselves at a critical moment on cavers trying to following the advice. We have an example of it all going wrong in Alex's anecdote above.
If I retie my cows-tails once a year I will take care to get it right, if I retie my cows-tails once a week my odds off getting it wrong will increase, compounded by human nature, I'm likely to get lazy.
I will answer your first paragraph separately.
I am uncertain whether to either applaud your brutal honesty or to assume you were being lazy and using the term ?I? to really mean some other person. For the avoidance of accusations that I am getting at you, I will use the term ?this person? and thus not imply it might be you.
The short answer is that such a person would be considered what I would call as a ?walking disaster? and likely to have given up SRT because of either the frightening experiences they have had or else found no one will go with them.
The longer answer is best explained in terms of probabilities and frequencies.
Let us assume this person undertakes ?a? SRT trips per year. (a will thus be one or more in value.) And on each trip there is a probability of ?b? that this person will fall on their cows tail in such a way as to suffer a serious consequence (sever injury or fatality). (b will thus take a value of between zero and one.) The option you raise is that either this person ties their cows tails properly and hence saves them self from the serious consequence when they fall or does not tie them properly and thus suffer a serious consequence when they fall. (Note b includes the probability of this fall.) Let us take the probability of tying them improperly as ?c?. Thus the probability of tying them properly is ?1-c?.
So we have two partial probabilities b * (1 ? c) where this person gets away with the fall and b * c where they do not. Work on human factors usually cites a value for c of around 1 in 10,000 for getting a simple task wrong. So clearly if this person is diligent, then the partial probability of getting it wrong is small compared to the probability of getting it right.
But you were suggesting this person was grossly incompetent so c takes a much larger value. But in such circumstances I would argue that we also need to look at the impact that such a level of (in) competence would have on the other risks that one takes with SRT. So on each trip this person will put their gear on at least ?x? times, tie ?y? knots in rope, and have ?z? other opportunities for getting things wrong. Now x, y and z will all take values of at least one and probably somewhat higher perhaps up towards ten. I will argue that it is appropriate to use the value of c to provide a probability that this person will get any of these acts wrong and thus leading to a serious consequence. So in this case we need to factor the value of a into our probabilities to get frequencies so that:
a * b * (1 ? c) is the frequency that this person gets away with the fall;
a * b * c is the frequency that this person does not get away with the fall; and
a * (x + y + z) * c is the frequency that this person has a serious consequence through some other stupid act.
I trust you can see that as b is much smaller than x + y + z, then the frequency of this person not getting away with a fall is trivial compared to the frequency that this person has a serious consequence through some other stupid act. One might also argue that the value of b rises in the light of the gross incompetence of this person, but it will still be less than one, so there remains a benefit in taking the precaution. Hence my term ?walking disaster?. I trust you have not known too many such characters.
I must admit that I still don't understand how one can effectively clean one's cows tails without partially untying the knots. Leaving dirt in the crevasses of the knots seems like a good way to reduce the life of the cows tail.
