Bent at Devils?

[PfcAJ]

It seems that there have been quite a few people getting bent (to some degree)
at Ginnie. I have heard of at least 6 people, and I personally know a few of
them. What is so special about Ginnie that causes this high number of incidents?

Improper decompression? Obviously. But even when people are within the
parameters of their tables or computers, it's still happening.

Lack of proper hydration or nutrition? Maybe. But wouldn't we see a similar
frequency at other caves?

Lack of diver skill? Once again, possible. However, we would still see divers
unable to hold stops and stay true to a schedule getting bent at other sites,
which just isn't happening nearly as often.

So what could it be? Brian (Litehedded) and I have been doing some thinking
(and consulting with other local cave divers) about what is so specific to
Ginnie compared to other places. We have determined that the first few hundred
feet of the cave is the most likely culprit.

The cave will be referenced from the exiting diver's point of view:

The depth change from the Junction Room area to the breakdown room past the
Keyhole is about 15-20ft. This is a rather high percentage change that occurs
quite quickly. Divers with longer bottom times may have more drag associated
with them (stages, scooters) that increases their exertion on exit to reduce
their speed through this restrictive area. Strike one.

The Gallery passage is the other problem area. Divers have a choice: Either ride
the ceiling, or ride the floor. If a diver rides the ceiling, he/she must descend
to the bottom (another 15-20ft) to exit into the Eye/retrieve deco bottles. I
personally feel that riding the ceiling is a poor choice. While a dive might be
'off gassing' across this shallow section, bubble formation is probably occurring.
The drop down to the Eye passage or to retrieve deco bottles will temporarily
compress those bubbles which would allow them to bypass the body's most
efficient bubble filter: the alveolar capillary bed in the lungs. Strike two.

Another potential issue is the amount of exertion required for entering the
cave. While techniques can be employed to reduce this effort (reading the cave,
using eddy and staying out of the flow, strategic pull and glide, streamlined equipment), lets face it, this isn't a no flow cave. Exertion may result in increased inert gas loading. Couple this with the factors I listed above, and we have a recipe for
DCI. Strike three.

Divers are often in a rush to get on the 20ft bottle. A slower ascent with stops between the Cornflakes and the Keyhole, plus the usual at 50ft, 40ft, and 30ft could make a marked difference in DCI incidents (both clinical and sub clinical). A slow (6 minute minimum) ascent on oxygen from 20ft to the surface is also cheap insurance.

While a diver might be reasonably hydrated at the beginning of the dive, thick undergarments needed to manage long exposures and deco times can contribute to overheating and subsequent sweating and increased fluid loss in the beginning portion of the dive. Divers with long dive times should consider some form of in-water hydration. Some divers are having success with deco or stage mounted camelbaks with either water or a sports drink such as Gatorade or PowerAde.

I understand that the plural of anecdote is not data, but we have limited
resources to draw from. I hope that this makes you consider your profile and
resulting decompression.

To make some concluding remarks, excellent hydration, nutrition, fitness, and a
smooth ascent using all the available research as a guide is the secret. We have
to use all the tools available to us to stay safe and not get injured. While the only sure-fire way to prevent DCI is to not dive, if we stay current and constantly evaluate our practices, we can only hope to remain as safe as possible.

 

[siikik]

Interesting hypothesis. But the biggest variable is still the diver's own physiology. There's just no absolute formula...



Ken

 

[SuPrBuGmAn]

...and the dive profile itself. Its possible to have long exposures in that cave, with the amount of passage available, and now depths up to 150' way the hell in the back of the cave... its possible to soak up a good bit of nitrogen.

There are a ton of variables, and just as many assumptions would have to be made to come to any conclusion.





Dive conservatively and follow what you've been taught/learned about decompression.

 

[DA Aquamaster]

I think Ginnie also sees a lot of diver traffic - it would be interesting to see the hit rate per hundred thousand dives. I am not 100% sure there would be any difference between Ginnie and other locations once you correct for traffic numbers. 6 sounds like a lot, but 3 somewhere else with only 1/3rd the number of dives over the same period of time would statistically be a lot higher.

It is also open all night long making it much easier to do multiple deco dives per day than other areas that close earlier and or are farther from fills and I think a third deco dive per day greatly increases the risk.

And it is high flow, at least on the mainline and many dives at Ginie are what are considered "working dives" with more potential risk. It also impacts deco and doing deco in the ear is not my first choice, especially if it is busy with the potential for multiple teams doing deco at the same time as a nice slow ascent to the 20' stop is a bit of a PITA there and there are limited places where you can relax out of the flow on deco. I much prefer the eye for deco.

Otherwise I generally agree that it offers an interesting combination of high flow/high exertion, saw tooth depth changes on exit and some factors that make a slow and smooth ascent potentially more difficult.

 

[ucfdiver]

Dive conservatively and follow what you've been taught/learned about decompression.

I'm starting to think that conservatism goes further ABOVE the water than an extra few minutes below the water. I've talked to 7 people who have been bent here recently (as in, we talked recently, some were bent a while back), and ALL of them blame dehydration.

 

[SuPrBuGmAn]

That'll do it... at any site.

Just so happens that Ginnie is probably about the most visited cave in the world. I wonder if statistically, its not one of the sites with the least amount of bent divers, with somewhat comparable profiles.

 

[ucfdiver]

That'll do it... at any site.

Just so happens that Ginnie is probably about the most visited cave in the world. I wonder if statistically, its not one of the sites with the least amount of bent divers, with somewhat comparable profiles.

Out of 9 cases that I'm aware of in caves last month, 5 were Ginnie. The other 4 I'm unaware of, they could be Ginnie as well. I seriously doubt that Ginnie dives are THAT disproportional to all other caves. Manatee, Little River, Peacock, Telford, Madison, are all in the nearby area, and at the time, weren't flooded. I'm guessing they at least combine to equal Ginnie's traffic, realistically more.

 

[SuPrBuGmAn]

Little River and Peacock get alot of traffic. Tons of people have gotten bent at Little River, but its also one of the first sites to blow when things get nasty. Peacock is shallow(aside from a couple spots), it doesn't have profile to bend people easily. Peacock probably gets nearly as much traffic as Ginnie, but at a much friendlier dive profile its not as big of a problem. Nor is the flow.

Madison limits teams. Manatee limits teams and rarely hits its limit. Telford is only river accessible and its shallow.

 

[DA Aquamaster]

Exactly, a 2 hour dive in Peacock is still often a no deco dive, even if you go up the Olsen side and upper orange grove is essentially the same, but with very easy deco opportunities in the basin. And no significant flow so they are only light to moderate dives in terms of physical exertion.

The profile is significantly different at Little River - you get fairly deep pretty quickly and are in deco by the time you get through the Florida room - but then you are also close to thirds anyway if you swam in , so anything farther puts you into stage territory.

I suspect that statistically - number of hits per number of dives - Little River is worse than Ginnie since:

1. Many divers come up from 90 ft to 40 ft a lot faster than they should
2. Many divers again probably ascend in the cavern from 40ft to 10ft faster than in many other systems, and
3. It is tempting to haul yourself out of the sink and up the steps too soon after a deco dive and that post dive exertion can cause problems that might not otherwise surface.

 

[LiteHedded]

IMO it's easier to have a smooth curve on deco at LR
it doesn't have the sharp sawtooth action on exit you can get at ginnie