Well depends on what you mean by fragile and what type of cable. A typical plastic (PMMA) cable has a pull strength to 5% elongation of like 40 lbs. That is tough stuff and can be flexed (quarter bend) 10,000 times for a loss of 1 dB. But if you bend a large single core fiber over a sharp corner you will have trouble. 1mm fiber has a bend radius of about an inch for a half dB (10% more or less) loss in signal. For bigger core fibers the diameter gets bigger (2 mm has a bend radius of 45 mm) for the same 10% loss. The big advantage of the multi-core fibers is that they can be bent over a 1mm radius and still transmit 95% of the light. I haven't put any of my fibers into an Instron machine to see how hard it is to pull one apart, but I suspect it will be very difficult. I have never broken a cable in half in more than 1500 dives, but I have seen cables get pinched so that they stopped transmitting. if that happens cut off the pinch part and you should be good to go.
Even if they are tough, Dave's advice is correct, always carry a spare and if you roll your own carrying a few spares doesn't cost much.
Bill
