This thread is prompted by a number of accidents, but the most recent was yesterday, when four people died in a sea cave in Italy, because they followed a guide into an environment where they didn't have the training to cope with the complications that ensued.
This is not a diatribe about "don't dive in any overhead environments without appropriate training." That's an easy answer, but it isn't the reality of what people actually DO out there. LOTS of OW divers dive, or are led through sanitized wrecks or "benign" overhead environments like the Cathedrals off Lanai. One really doesn't hear about incidents from those dives, and that's probably due to the relatively benign nature of the challenge. Thousands of divers do the cenote dives in MX each year, and except for a single recent accident, one doesn't hear about incidents there, either. That's probably due to the careful (but voluntary) rules that have been developed for those dives.
But one DOES hear of people dying in overhead environments. People get trapped in wrecks or lost in caves . . . All too often, those people are following guides. So how is the OW (or just purely recreationally trained diver) to assess whether he should or should not do a given dive that's proposed to him?
The BIGGEST risk in overhead diving is getting lost. If you can find the exit, you will almost certainly survive the dive -- but if you can't, you will drown. Overheads are complicated for two reasons: One, there can be complex navigation, with multiple choices of path, of which only one or a few will result in a successful exit. Two, one has to be able to see to navigate, and overhead environments often involve conditions in which the visibility can rapidly decrease to low or zero.
So this offers a few ideas for assessing the risk of a proposed dive. If the overhead environment has complex ramifications (multiple navigations choices) you don't belong in there. That requires a guideline, and the ability to follow the guideline in the dark. If you can't do that, don't go in.
If the overhead environment has significant silt or other unstable sediment (or material on the walls or ceiling -- you don't have to have bottom sediments to blow the viz) then you require a guideline, and the ability to follow it in the dark. If you can't do that, you don't belong in there.
If the overhead environment involves ANY kind of restriction -- defining that as a place where two divers can't swim comfortably side-by-side -- you don't belong in there. If you have any problem beyond the tight spot, you won't be able to negotiate your exit with anybody assisting you, whether that's air-sharing or just calming you down. The only overhead spots appropriate for untrained divers are generous ones.
A place like the Cathedrals, where there are multiple exits, with a coarse sand bottom and tons of light, is pretty benign. "Sanitized" wrecks, like the Cape Breton in Nanaimo, are reasonably benign (yeah, the CB is not because it's deep, but it's the idea). If you can easily see your exit from your entry, straight across, it's likely not to be too bad.
If you are following someone into the dark, and you don't know what the topography is of where you are going, and you don't know the composition of the bottom sediments, and you can't run a guideline or follow one blind . . . be very cautious about your decisions to follow someone into an overhead environment. They can, and do, kill.
This is not a diatribe about "don't dive in any overhead environments without appropriate training." That's an easy answer, but it isn't the reality of what people actually DO out there. LOTS of OW divers dive, or are led through sanitized wrecks or "benign" overhead environments like the Cathedrals off Lanai. One really doesn't hear about incidents from those dives, and that's probably due to the relatively benign nature of the challenge. Thousands of divers do the cenote dives in MX each year, and except for a single recent accident, one doesn't hear about incidents there, either. That's probably due to the careful (but voluntary) rules that have been developed for those dives.
But one DOES hear of people dying in overhead environments. People get trapped in wrecks or lost in caves . . . All too often, those people are following guides. So how is the OW (or just purely recreationally trained diver) to assess whether he should or should not do a given dive that's proposed to him?
The BIGGEST risk in overhead diving is getting lost. If you can find the exit, you will almost certainly survive the dive -- but if you can't, you will drown. Overheads are complicated for two reasons: One, there can be complex navigation, with multiple choices of path, of which only one or a few will result in a successful exit. Two, one has to be able to see to navigate, and overhead environments often involve conditions in which the visibility can rapidly decrease to low or zero.
So this offers a few ideas for assessing the risk of a proposed dive. If the overhead environment has complex ramifications (multiple navigations choices) you don't belong in there. That requires a guideline, and the ability to follow the guideline in the dark. If you can't do that, don't go in.
If the overhead environment has significant silt or other unstable sediment (or material on the walls or ceiling -- you don't have to have bottom sediments to blow the viz) then you require a guideline, and the ability to follow it in the dark. If you can't do that, you don't belong in there.
If the overhead environment involves ANY kind of restriction -- defining that as a place where two divers can't swim comfortably side-by-side -- you don't belong in there. If you have any problem beyond the tight spot, you won't be able to negotiate your exit with anybody assisting you, whether that's air-sharing or just calming you down. The only overhead spots appropriate for untrained divers are generous ones.
A place like the Cathedrals, where there are multiple exits, with a coarse sand bottom and tons of light, is pretty benign. "Sanitized" wrecks, like the Cape Breton in Nanaimo, are reasonably benign (yeah, the CB is not because it's deep, but it's the idea). If you can easily see your exit from your entry, straight across, it's likely not to be too bad.
If you are following someone into the dark, and you don't know what the topography is of where you are going, and you don't know the composition of the bottom sediments, and you can't run a guideline or follow one blind . . . be very cautious about your decisions to follow someone into an overhead environment. They can, and do, kill.
