I cave dive on a regular basis with two other guys. We've dived together as a team for nearly 10 years. I'm late 60s and single, the second guy is 50s and has a partner but no children, and the third is early 40s with a six-year-old, who he has every intention of seeing grow-up into adulthood.
We often dive in a system comprising a complex maze of 8kms of underwater tunnels. Some are large, and would fit several divers across, but some are small, and you can barely squeeze through. The only entry to and exit from this system is a small pond, about 6 feet across and 4 feet deep, just big enough for one person to get in at a time. Then you scrunch yourself up, and drop down through a slot to enter the system.
We'd generally go about 700m into this system, making up to 13 seperate navigational decisions (left? right? straight ahead?) which we have to reverse precisely to get back out at the end. This is all completely underwater, there's no air anywhere except for two air pockets hundreds of meters apart. As I like to say, in cave diving there is no UP – there is only OUT!
It all sounds pretty dangerous, right? Wrong.
NAVIGATION. The whole system is set up with fixed lines, each of which has a numbered marker every 50m or so. Before each dive, we consult the map, and plan exactly where we're going to go. I commit that plan to memory, write it down on a wrist slate, and also in a notebook which I take underwater. All three of us do this independently. Underwater, when we come to a junction, each of us checks the direction to go, then marks the exit direction with a personal marker. If anyone makes a mistake, for example, turns in the wrong direction, or forgets to leave a personal marker, the other two pick that up immediately. On the way back, when we get to each junction, each of us checks that it's the junction we expected, and we can see our personal markers. Each individual's markers can be distinguished by feel alone, so we could get the whole way back, separately, in total darkness, if we had to. So the odds of us getting lost in the system are very low.
LIGHT. These caves are absolutely pitch black, so naturally you need a torch. In fact, nine torches! Each of us individually has a multi-thousand-lumen canister battery light, plus 2 backup torches, each of which would last the whole dive. I could also navigate by the light of my dive computer screen, and I'm considering carrying a cyalume chemical lightstick as well. So then I personally would have five different sources of light, and we'd need 11 sources of light to fail before the team would be left in the dark. The risk of this happening is basically zero.
GAS. Each of us has two tanks in a fully redundant setup. If one side fails, we just go to the other and call the dive. In fact, our gas planning allows one diver's entire gas supply to fail, at the point of maximum penetration, and either one of the other two divers could get that guy back, plus himself, without relying on the third diver at all. However, gas is certainly a limited resource underwater, so it's always on our minds, and all three of us will turn the dive as soon as anyone hits their safety limit.
There's lots more equipment involved, but let's leave it there for the moment, and turn our attention to...
DRIVING! Each of us lives >400 km away from that system. So there and back is a five hour drive. During that drive, you could fall asleep and run off the road; have local fauna run out in front of your car; get head-on crashed by drunken drivers, and so on. Several of those are external risks that are not under our control.
So the simple fact of the matter is this. Our cave dives are almost certainly SIGNIFICANTLY SAFER than driving to and from the dive site! The cave dives carry significant potential risks, but most of those are mitigated with proper training and equipment. Whereas there's not much I can do to stop a drunken driver running head-on into me.
Certainly there are risks like tunnels collapsing and blocking the exit. But statistically, I'm sure that those are orders of magnitude less likely than having a heart attack, or falling over and breaking your neck.
Hope that helps :-)