Swim throughs - what could possibly go wrong?

[victorzamora]

it is safe to assume that you have a buddy and both have suitable qualifications to be diving in the environment.

I know this isn't the answer you're looking for, but:

You've been a stickler to agency rules and guidelines in other threads, so I'll answer in that same vein. If a diver has overhead qualifications (as is considered suitable for the overhead environment) then there's no reason that diver shouldn't be expected to answer that question himself.

 

[Foxfish]

I know this isn't the answer you're looking for, but:

You've been a stickler to agency rules and guidelines in other threads, so I'll answer in that same vein. If a diver has overhead qualifications (as is considered suitable for the overhead environment) then there's no reason that diver shouldn't be expected to answer that question himself.

That would depend. Have you done any overhead training? What type? Do you think it prepared you well for assessing the risks associated with diving the environments I described in the OP.

 

[DivemasterDennis]

There are so many variables involved in the question that are not covered by any of the assumptions that risk analysis is not possible. Any overhead environment presents dangers, not limited to getting lost or "stuck." Lack of buoyancy control may result in hitting a tnak valve or first stage or bcd on the ceiling or wall of the swim through and damaging it, creating an emergency not otherwise anticipated. Configuration of the swim through may or may not permit sharing of air without substantial additional stress or difficulty. Bottom composition is important too. Even sand can be kicked up and limit the visibility, particularly if something other than an event-free swim thorough occurs. Debbie and I do a lot of swim throughs, and we pass on some that aren't "right" because when we dive together we are no usually equipped with the "overhead environment gear" that one should have if that is part of a dive plan. A 20 meter swim through open at either end, spacious, with a non-silty bottom will still present potential danger not present in a non-overhead environment. That awareness is important.
DIvemasterDennis

 

[TSandM]

• There is only one clear path and no chance of getting lost;
• The floor is course sand that won't silt even with a group of divers swimming through the cavern;
• It is so spacious that many divers can pass through at the same time;
• The cavern has multiple large entries and exits; and
• It is well illuminated.

You've eliminated many risks of overhead diving in your assumptions. If you can't silt out the viz, and you can't get lost, and there are lots of places to get out, and you could easily share gas with another diver, then the remaining factor of overhead diving is simply that you can't panic and bolt. The Ginnie Ballroom meets many of your criteria, apart from multiple exits and light, but a woman died there because she got stuck to the ceiling and couldn't sort her buoyancy out to leave the cavern. I believe she drowned with gas in her tank.

You will read many discussions of diving risks, and some of them are what a good friend of mine calls Little House on the Prairie scenarios. I never watched the show, but apparently every episode would involve situations where many implausible things went wrong. Any of us can posit a situation where so many failures occur that the dive is not salvageable, but those situations are (thank God) not often seen in reality.

If you are swimming through a huge, well-lit space like the Cathedrals, that you can't silt out and you can't get lost in, it's highly unlikely anything bad will happen unless someone has a problem and panics. Panic kills in diving, but it particularly kills in overhead environments.

Most of us who have a fair bit of diving experience are going to be able to cope with a flooded mask, or a freeflowing regulator, or a lost fin, or some other fairly normal malfunction, without deciding that the only option is a direct and frantic bolt for the surface. We are unlikely to get into trouble in the Cathedrals, or swimming through the aft section of the Rhone. But I have read a hair-raising account of a man whose wife almost died in Devil's Throat, by mistaking a crack that admitted light for a route to the surface, and getting stuck, and panicking. So even in well-lit and reasonably commodious swim-throughs, risks remain, especially at significant depth.

Did I do swim-throughs before I had overhead training? Yes, I did. Did I consider each situation carefully, knowing that overhead environments are in general inadvisable? Yes, I did. Did I get in any trouble? No. Do I think the likelihood of trouble was high? No. The problem with taking those examples and running with them, though, is the slippery slope concept. If it's okay to swim the Cathedrals, is it okay to swim the cavern at Hole in the Wall in Florida? A family of three almost lost one of their members by answering that question in the affirmative.

I think overheads, even simple ones, up the ante on the risk of the dive. They are appropriate for experienced divers who have some familiarity with their reaction to stress or malfunction. They should be chosen carefully to meet the criteria listed in the original post. And they should not lie at depths where narcosis is a major factor.

 

[Foxfish]

Lynne, I think we're on the same page with this one - there is a first time for everything

. Experience and common sense go a long way in assessing the risks associated with this kind of diving. Discussions like this can help highlight some of the less obvious risks.

Our local waters can get very rough and the currents in some areas around the island we dive are so strong that diving is unsafe. Boats do capsize and people drown. The more important consideration for me is understanding local conditions and knowing when not to venture out for a dive.

The skippers on the charter boats are experienced locals who know and understand the conditions. They can tell at a glance where the visibility is poor or where the currents are too strong or the swell and surge is going to be too high. They know the best places to dive for the prevailing wind conditions. They know the limits for safe diving and will choose locations taking into consideration the experience of divers. They make assessments of the conditions both before they arrive at the site and on arrival at the site. If they consider a planned site unsuitable they will move on to the next.

I was out on the weekend doing my solo course in conditions I wouldn't normally dive. It was more a case of being uncomfortable than unsafe. Winds ranged from 20 to 35 knots and even in the protected areas the seas were running at around 1.5 m. The skipper pulled up to the first site he had in mind and then at the last moment pulled away because of poor visibility.

We anchored at the next site and there was some surface current. We were advised to plan the dive so that we were initially swimming into the current. The boat had a long mermaid line out the back. Most of us had no problem with the current. We dove to about 20 m and there was little surge. There were no caverns. The dive was okay if a little boring. We were on a course after all. At the end of the first dive a group of about 7 tourist divers were seen floating out the back away from the boat. They evidently could not fin back to the boat. The skipper had to jump into the small rescue inflatable and pick them up. He managed to just get them all on board in one trip. The inflatable was full of water on return. That could have easily turned into a disaster.

The point being that understanding local conditions and the limits for safe diving is the important consideration here. What some divers find relatively benign can be a disaster for others. For the caverns we dive, being able to lay lines and learning special finning techniques are irrelevant on a good day and of no benefit on a rough day.

Frankly if I thought it was necessary to lay a line to make entering a cavern safe, or needed a torch to find my way I wouldn't enter the cavern. I've been swimming through these caverns on charters with 40 other divers and have had no problem with visibility. I'd guess that if you tried to enter the cavern with a 4 m swell running visibility would be a problem but that would be the least of your worries.

 

[victorzamora]

Have you done any overhead training?

Yup

What type?

Full Cave.

Do you think it prepared you well for assessing the risks associated with diving the environments I described in the OP.

In literally every way I could imagine.

 

[Foxfish]

Yup


Full Cave.


In literally every way I could imagine.

Did you learn anything on identifying and mitigating the diving risks associated with environmental factors like wind, waves and ocean currents.

 

[fbk]

Those swimthroughs constitute the majority of dives I do here. Is there potential for things going pear shaped and ending badly? Absolutely. I have been stuck in one, wedged in a hole, and had reg and mask ripped off my face by massive surge. My occy (on my shoulder strap at the time) was also swept away behind me somewhere inaccessible. For a few seconds (it seemed like much longer) I thought this is how I'm going to die. It was in about 4m of water. I doubt I would have been the first. From that day I switched to wearing a bungeed backup.

I have been stuck in other places, albeit briefly, but enough to make me think "if I went OOA at this very second, it wouldn't be good. To be honest my biggest fear in the really tight spaces is the reef shifting or collapsing. Extremely unlikely, but when you see the structure, its not like it has been that way forever. Maybe it won't move for a million years. Maybe the day it moves is the day of my next dive. The risk of getting lost, or silted out, or zero vis due to light failure, is practically nil.

I am cave trained, but these are single tank dives usually hunting crays. I am aware of the risk, no matter how small, or how deceptively safe these dives are.

 

[Foxfish]

Ahah. Someone who speaks the same language. Have you found the cave training helpful in diving these swim throughs. Would you consider it essential training before entering one?

I dive mostly off the charter boats around Rottnest. What areas do you like to dive?

 

[fbk]

I dive all around Rottnest, usually on private boats. I was going into those swim throughs long before any cave training. Regardless of whether they are overhead environments or not by definition, I personally wouldn't consider them as such in terms of training or equipment required, any more than swimming under the boat. The hole I got stuck in... I probably had open water over my head. The main dangers (as I've already experienced) are getting wedged/stuck, and having no access to air while stuck.