Not caving rope related but...
In a report on dynamic climbing ropes Pitt Schubert, President of the UIAA safety commission found the following....
1. Ropes cannot break in the tie in knot, or at the running belay.
2. Use of twin ropes has cut down on breakage's.
3. There have been no known rope failures in sport climbing
4. Petrol, Diesel, WD40, Coke and sea water do not damage ropes.
5. Autan (insect repellent), although damaging to plastic, was not found to damage ropes...in fact strength was slightly increased.
6. UV radiation does not damage ropes. Nylon is UV stabilised and only the colour will be lost.
7. Standing on a rope loaded over a right-angled metal edge with three times body weight did not reduce a ropes strength.
8. Standing on a rope in the snow with crampons did no damage. Neither did standing on it on rock with a 75kg body weight. In a further test crampon points were forced right through the rope with no strength reduction/damage occurring!
9. The suggested life span of 10 years which has been given for ropes is to help the user determine life span . However, after contact with ICI it was found that although after 10 years there was a measurable degradation in nylon (not just in ropes, but all nylon textiles) ageing itself would not cause a rope to break, unless it was loaded over a sharp edge.
10. Top roping damaged ropes, but the damage was visible and could be felt. The same applied to damage from stonefall.
However, lest we become complacent...
1. Any rope can break when loaded over a sharp edge. It is not possible to produce a rope that is strong enough not to break when loaded over a sharp edge, however, the maximum chance for survival is with a new rope.
2. Car battery acid damages ropes and cannot be visibly detected.
3. Ropes soaked overnight in urine (!) had their strength reduced by 30%. However, this was only relevant when the rope was loadedover a sharp edge.
4. The strength of frozen and wet ropes was reduced but again, unless the rope is loaded over a sharp edge, it would not matter.
The 10 years life span mentioned is for an unused rope. As soon as that rope is used the clock starts ticking. Five years is given as the working lifespan unless the 10 year time period comes sooner... so in effect you have three years life left (the rope that is - taking advice off the internet could possibly reduce yours considerably
!!).