Recompression Chamber Under The Boat?

[Mark Michaud SELAUSAR]

I know this supposed to be a friendly (ask anything you like) forum but what a complete "Scuba Snob". It was a simple question, and you not only insult me, but the other members of this forum. I can't think of a better group of people to ask, than the scuba divers here. Obviously, you think they're incompetent to answer questions... but you are.

I would ask you more questions about your reply concerning a second ascent and CNS toxicity, but it's obvious by your arrogant response, you have your head buried up your own... well, you know where. Don't reply to any more of my post, as your type of help is not needed.

FWIW, Doppler has forgotten more than most on this forum have ever learned. He does not post much (look at his join dates and number of posts) but when he does we would all take care to listen. The question you asked is not really simple and could have dire implications. Learning deco procedures and theory is not that difficult, hence referring you to said book. Learning deco procedures and theory is necessary if you are going to dive, alot, as all dives are decompression dives. Please don't take this as a scolding or anything. The written word generally comes across without emotion unless you are a novelist. This is only written to give you a perspective of the caliber of persons on this board. There is a lot of great information that can be obtained here from people who have tons of experience in what they post about. I generally will not post about things I have no first hand / hands on knowledge about. In this case I don't know Doppler personally but I know a ton of people who do and his words are definitely worth a listen. Don't stop asking questions, the whys are important, the whats are necessary. We need both if we want to master this discipline. Too many only learn the whats and never really know why. Mark

 

[TSandM]

I know this supposed to be a friendly (ask anything you like) forum but what a complete "Scuba Snob". It was a simple question, and you not only insult me, but the other members of this forum. I can't think of a better group of people to ask, than the scuba divers here. Obviously, you think they're incompetent to answer questions... but you are.

Oh, my goodness. There aren't very many people in the Internet world on diving who have my undiluted respect, but Steve is one of those people. If he gives you an answer, it's best to read it carefully and reflect on it, whether you find it palatable or not.

You're thinking and asking questions, and those things are good. But considering hypotheticals can sometimes push you into contemplating things that border on the absurd. In the scenario you posit, where we need to start is why the diver exceeded their NDLs by so much to begin with . . . because that just shouldn't happen. And if it does, and the diver makes it onto the boat in good condition and can be put on oxygen, that's the answer. The boat is stable, and dry; CPR can be done there, oxygen can be provided there safely, and a helicopter or rescue boat can retrieve the victim easily there. Put that person in the water, and you have an unstable and much more difficult environment to monitor.

People who do dives with planned decompression obligations, do a lot of planning to avoid ever being on the boat with a lot of omitted decompression. There are omitted decompression schedules, and boats which are supporting such divers carry supplies to support those types of treatments, if chamber availability is remote or unreliable. Such dives are very high risk, and the people who do deep diving in remote places do a lot of heavy-duty thinking about what they are doing, and the possible consequences, and they spend an enormous amount of time trying to set everything up so that they will never face the scenario you describe.

So, it's good to do intellectual exercises, but that's what they are. Your scenario needs to be addressed at the prevention step, beginning with planning and continuing with situational awareness in the water, long before one might address any questions of in-water recompression.

 

[Akimbo]

I compliment you for asking this question. I concur with most comments so far and am usually among the first to take issue with “take more classes” and “you have no business thinking about this” types of advice (not that this dominated in this thread). I do find a couple factors in your scenario improbable.

…
Let say for example, for what ever reason, on the first dive you exceed your no-deco limits and don't have enough air to make the proper deco stop at 20 feet. During a short surface interval, say one hour, no signs or symptoms of the bends manifest, but you're still worried. …

Exceeding no-D limits enough to require a 20' stop, rather than just a 10', is pretty significant. It is marginally likely a recently-trained recreational diver could without carrying unusually large gas supplies. Second is one hour isn’t a short surface interval when you are worried.

Missing 10 minutes at 10' and returning in less than 10 minutes for your omitted decompression might elicit different opinions — depending on your expertise, support, and proximity to a treatment facility. I personally find it egregious that this discussion isn’t part of any certification that sanctions unsupervised diving beyond 40'. There have been a number of discussions on this board that examines the trade-offs and is a good primmer for continued exploration of the subject.

In any case, I suggest keeping your DAN insurance paid up. Staying in no-D limits isn’t a guarantee of avoiding DCS and unforeseen problems, as your question suggests, do occur.

 

[debajo agua]

When I purposed this question to my instructor, I saw a stressed response... I picked up on it, and decided not pursue the line-of-questioning anymore, for the time being.

From what I've gather here in this forum, it can be done; although, it's a really bad idea, due mainly to the fact of a risk of air embolism/stroke underwater and not knowing the parameters of a successful re-compression and subsequent decompression. My make-believe scenario was meant to illustrate meaning, but probably served more as a distraction from intent of my question.

Once again, I gain some knowledge; learned some new terms; and found a really good case study to drive home the point (see Mia Tegner Incident). Good stuff

 

[Bubbletrubble]

Once again, I gain some knowledge; learned some new terms; and found a really good case study to drive home the point (see Mia Tegner Incident).

The Tegner incident was a very sad one that occurred here in San Diego. She was a Scripps research scientist and very experienced diver who was conducting a fish survey at the Yukon dive site. She was essentially solo-diving. After other divers had exited the water, they witnessed Mia surface. She stated that she hadn't had enough gas to conduct a safety stop. She was given a tank with 800 psi connected to a reg and BCD. She re-descended and was later found on the bottom. The rest of the details are contained in a 2001 ScubaBoard thread about the tragedy:

More info from Marc (a member of Seadeucers):

Mia Tegner had completed a 30 min dive with a max
depth of 70' on the Yukon. I believe there was about
a 90 min surface interval and then the 3 person dive
team did a dive on the El Rey. Mia was doing something
related to her research on the dive and the dive
buddies were not in constant contact. The other 2
divers surfaced after 35 minutes. Mia surfaced 5
minutes later indicated she did not have enough air
to complete a safety stop. A tank with 800 psi and
BC and regulator attached was handed to her and she
descended holding the rig in her hands. After a
few minutes this tank floated to the surface. Her
husband descended with 800 psi to search for her. At
200 psi he surfaced, asked if she had surfaced and
descended again using the remaining air in the tank.
The radio on the boat was not functioning
so flares were shot and another boat responded and the
Lifeguards were contacted.

The Lifeguards responded pretty quickly but the
regular patrol boat only contains a minimal scuba
rig which limits the Lifeguards search to a maximum
depth of 40 feet. The Lifeguards did search to a max
depth of 40 feet and found nothing. A bit later (15-20
min ??) a second lifeguard boat arrived and a deeper
search was performed. The lifeguards descended the
anchor line of the boat to a depth of 15 feet and then
dropped straight down and found Mia close to that
spot.

Mia was wearing a drysuit and an Atpac style BCD.
The Atpac was a very popular BCD with back mounted
wings. The backplate is hollow with a trap door at
the bottom. Lead shot is normally stored loose inside
the backplate. Over a period of time it was pretty
common for the lead shot to form into a big clump
which made it difficult to fall out when the trap door
was opened.

With no air in her own tank positive buoyancy could
likely only be obtained by orally inflating the BC.
The autopsy ruled found the cause of death to be
drowning.

All of this for a safety stop.
It makes one wonder how often this kind of recklessness occurs without incident.

 

[MXGratefulDiver]

The Tegner incident was a very sad one that occurred here in San Diego. She was a Scripps research scientist and very experienced diver who was conducting a fish survey at the Yukon dive site. She was essentially solo-diving. After other divers had exited the water, they witnessed Mia surface. She stated that she hadn't had enough gas to conduct a safety stop. She was given a tank with 800 psi connected to a reg and BCD. She re-descended and was later found on the bottom. The rest of the details are contained in a 2001 ScubaBoard thread about the tragedy:

All of this for a safety stop.
It makes one wonder how often this kind of recklessness occurs without incident.

Several mistakes were made ...

- allowing herself to get that low on air
- redescending
- redescending without securing her air supply
- diving a rig that wasn't functioning properly

As frequently occurs in diving accidents, it wasn't one mistake that led to a tragic conclusion ... it was a series of poor decisions and responses that led to a chain reaction. Had she broken the chain at any point, the accident would not have occurred.

It also points to how easy it is for an experienced diver to take basics too lightly ... and get bitten by simple things they knew better than to do ...

... Bob (Grateful Diver)

 

[Akimbo]

debajo agua: As time passes you will see that DCS is highly variable between individuals and even day-to-day, unlike most of the various flavors of barotrauma. You will see variations between yours and your buddy’s computer, decompression algorithms, and published decompression tables throughout the world and over time. Although it is prudent to treat your schedules as minimum mandates, the reality is you could still get bent following them and probably won’t get bent when violating them (within recreational ranges). Obviously, safety stops are just that — optional but a good idea.

I don’t see the Mia Tegner tragedy as decompression related as opposed as a poorly executed reped. It is entirely possible the autopsy missed a medical cause for her loss of consciousness that lead to drowning, hyperbaric or not. It is also possible that she was inadequately skilled at dealing with what should have been a minor inconvenience. As is often the case, there just isn’t enough information to draw reliable conclusions.

 

[Bubbletrubble]

It also points to how easy it is for an experienced diver to take basics too lightly ... and get bitten by simple things they knew better than to do ...

Among the other things that Bob mentioned, I think the Tegner incident highlights the danger of getting locked into the mindset that a safety stop is the sine qua non of safe diving. Many OW students exit class with the "always do a safety stop" mentality...to the extent that other important safety issues are ignored. There are certainly circumstances under which performing a safety stop can actually increase risk of diver injury. Although safety stops can enhance safety when properly applied, it's important to be a thinking diver and know when to forgo a safety stop.

After reading about the incident, I got the impression that the victim didn't have a good understanding about DCS risk, why safety stops are done, and the consequences of omitting a safety stop on a recreational no-decompression dive. Perhaps those issues were overlooked during her basic OW class. Perhaps she just forgot what she was taught.

The most likely series of events: Mia grabbed the additional rig, descended, and began to feel drysuit squeeze. The only way to arrest her descent immediately was to inflate the additional rig. Since it wasn't properly attached to her...it went up and she continued to plummet, separating her from her lone air source. Drysuit squeeze can be a very uncomfortable, painful experience. The squeeze may have hindered her limb movement to the extent that she couldn't react appropriately during the incident. At some point, she may have recognized that ditching her ATPAC BCD was an option, but she might have lacked the flexibility to complete the ditch. It's also possible that the pain from the squeeze affected her mentally, leading to an inappropriate panic-type reaction.

I don’t see the Mia Tegner tragedy as decompression related as opposed as a poorly executed reped. It is entirely possible the autopsy missed a medical cause for her loss of consciousness that lead to drowning, hyperbaric or not. It is also possible that she was inadequately skilled at dealing with what should have been a minor inconvenience. As is often the case, there just isn’t enough information to draw reliable conclusions.

Good point about the autopsy, Akimbo. The autopsy has to be done carefully in order to look for something like arterial gas embolism in the brain. I'm not sure if this was done in the Tegner case. I would think that the majority of cardiac causes would have been appropriately ruled out.

 

[ianr33]

I know this supposed to be a friendly (ask anything you like) forum but what a complete "Scuba Snob". It was a simple question, and you not only insult me, but the other members of this forum. I can't think of a better group of people to ask, than the scuba divers here. Obviously, you think they're incompetent to answer questions... but you are.

I would ask you more questions about your reply concerning a second ascent and CNS toxicity, but it's obvious by your arrogant response, you have your head buried up your own... well, you know where. Don't reply to any more of my post, as your type of help is not needed.

FYI: Steve is one of the most respected tech instructors around. Please don't piss off the few posters that have anything useful to say on this forum.

 

[RonFrank]

As a new diver I think you have enough to keep you busy for a while without getting into theory based DCS scenarios involving deco diving. Likely why your instructor blew off the deco questions if he did in fact have the answers.

I have been diving for a long while and have had just a couple of small deco obligations. Actually Coz is one of the few places I have dove where deco becomes tempting with the massive vis and cool stuff to see deep. Normally I am happy spending hours UW on 20' dives. Little risk and sun drenched coral beds is where it's at.

If is has not become apparent, deco theory is not an exact science. Same dive, one guy gets bent, one does not. I have seen this happen more than once.