Risks in Cave Diving

[Gary]

I took some simple assumptions an looked at risk involved in choosing a safe air reserve. The results were fairly sobering... I realize this could be bashed and twisted in any number of ways but the idea is still worth considering.

I took a rough estimation on cave diving risk is 1 death per 10000 events. And for the risky end a rough guess on the order of a 50% chance of surviving a dive to half gas (whether or not an accident/silt out or whatever may or may not occur).

In the range of gas reserve from 2/3s to 1/2 we are looking at a factor of 5000 times the chance of dying on a per dive basis. 2/3 of 3000 = 2000 psi, 1/2 of 3000 = 1500 psi. For every hundred pounds difference might increase or decrease risk by a factor of 10 times!

I ran the theory over a fitted normal distribution curves and it seems to agree with this general theory. With these assumptions the risk factor is predicted closer to 15 times per 100 psi in the vicinity of 2/3 reserve.

In the graph the 2/3's reserve being the assumed basis for the 1 in 10000 ratio we get the predicted 50% chance of death after 10000 dives. But the cumulative effect of additional risk or safety is clearly evident in repetitive diving as any 10 times risk is multiplied over a larger number of dives.


Whatever the assumptions used for the comparison the risk factor of 10 times per 100 psi would seem to be fairly universal. The cumulative effect of additional risk/safety over multiple dives could well decide your lifetime as a cave diver (or lifetime in general). Even over as little as 10 to 100 dives the tiniest violations of 1/3s has a noticeable effect on survival chances. And for those planning for a long career in cave diving additional safety margins might be worth considering.

<disclaimer: I'm neither a mathematician nor a dive instructor but figured this was interesting enough to share>