Recompression Chamber Under The Boat?

Hi All,

Okay, so far, when I've asked this question, the answer I received is, "technically you're right but we don't do that." End of story. So I'm going to ask it here:

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. So rather than risking a trip, to the closes hospital with a deco chamber that evening, you decide to take a second dive at, say 35 feet, re-compress and breathe off all of the residual nitrogen for 30 minutes or more.

I know that there's risk involved with this scenario, but given safety factors that all no-deco algorithm use, how risky is it?

One more thing, let's say e.g. that you didn't exceed the deco limits on your first dive but you exceed your ascension rate. Would re compression at a shallower depth, say 35 feet again, give you a better chance of avoiding the bends?

I believe this is one of those questions that instructors are obliged to tell their students, "Don't even think about it Buddy!" but something that many might do, if they found themselves in a similar situation.

Am I totally wrong on this one? If so, why?

debajo agua:

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. So rather than risking a trip, to the closes hospital with a deco chamber that evening, you decide to take a second dive at, say 35 feet, re-compress and breathe off all of the residual nitrogen for 30 minutes or more.

I know that there's risk involved with this scenario, but given safety factors that all no-deco algorithm use, how risky is it?

One more thing, let's say e.g. that you didn't exceed the deco limits on your first dive but you exceed your ascension rate. Would re compression at a shallower depth, say 35 feet again, give you a better chance of avoiding the bends?

I believe this is one of those questions that instructors are obliged to tell their students, "Don't even think about it Buddy!" but something that many might do, if they found themselves in a similar situation.

Am I totally wrong on this one? If so, why?

Click to expand...

Under the scenario you describe if I was not symptomatic, I might breathe off of some O2 or Nitrox on the boat and continue to monitor myself for signs of DCS. I would not do a second dive, period. Rather I would wait at least 24 hours before diving again.

First lots of computers have different algorithms, some more of a margin of error than others.

The problem I see is that if you get yourself in the situation where you may have a bubble or 3 floating in your system and you go back down for a "deco" there is the possibility of passing out( or others problems) and that is a very bad thing even at 35'. Much safer to thumb the next dive and make sure your ok before continuing.

I'm not a medical expert by any means, but this is something that's probably hard to quantify. However, there are possible reasons as to why redescending might actually be making things worse.

First of all, do a search here on ScubaBoard for the term 'bubble pumping'. Bubbles, once formed, are harder to get rid of than dissolved gas. If you've done a fast ascent or anything else to generate bubbles, going back down will shrink them, allowing them to bypass the lung filters into the arterial side of the blood system, where they're much more damage potential. Think 'stroke' or muscular equivalents. Formal in-water recompression protocols, commercial diving do effectively and for that matter hyperbaric chamber treatment all effectively redescend. However, the bottom-equivalent times are measured in hours, not minutes, and divers are warm, hydrated and well-monitored. Remember, a typical hyperbaric chamber ride is at least 3-5 hours. If you're potentially treating the same problem, were you planning to stay under water that long?

OTOH, some if not all deco diving protocols include provisions for missed mandatory decompression stops when not showing symptoms. Similar issues of warmth and what not apply though, since the recompression times are typically at least several times longer than the bottom times or missed stops. Also, you wouldn't want to arbitrarily graft an NDL dive schedule onto a deco missed-stop protocol generated with a different mathematical model and set of assumptions, since the assumptions of how you're diving that went into the table or computer model might be not be compatible. Re-analyze the dive series using the deco protocol's model, and fully understand the limits of the missed-stop protocol and whether you've done anything where it's not appropriate.

debajo, on the first it all depends on if you were sucking up air fast and took in a bunch of nitrogen, and missed 20' foot stop, that also means you missed 10' stop. Instead of waiting an hour, change tank out and go down and complete deco, you could go to 35' and slowly ascend to deco. Memorizing the navy tables of the dive your doing will allow you to do deco as your computer would be locked out more than likely.

Exceeding ascension rate is different and how fast, you may not feel anything for days then go to altitude or fly and then the next day KABOOM your feeling pain. So yes go back down and let the bubbles shrink then very slowly come up breathing as calm as can be and do a few stops, this also depends on what depth, if you were really deep you were lucky you felt nothing right away, and how long, close to deco as you stated no deco.

debajo agua:

Hi All,

Okay, so far, when I've asked this question, the answer I received is, "technically you're right but we don't do that." End of story. So I'm going to ask it here:

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. So rather than risking a trip, to the closes hospital with a deco chamber that evening, you decide to take a second dive at, say 35 feet, re-compress and breathe off all of the residual nitrogen for 30 minutes or more.

I know that there's risk involved with this scenario, but given safety factors that all no-deco algorithm use, how risky is it?

One more thing, let's say e.g. that you didn't exceed the deco limits on your first dive but you exceed your ascension rate. Would re compression at a shallower depth, say 35 feet again, give you a better chance of avoiding the bends?

I believe this is one of those questions that instructors are obliged to tell their students, "Don't even think about it Buddy!" but something that many might do, if they found themselves in a similar situation.

Am I totally wrong on this one? If so, why?

Click to expand...

There is no simple answer to your question ... which is why most instructors will tell their students "Don't even think about it Buddy!"

The fact is that bubbles will form in your body tissues, even if you do everything right. How those bubbles will interact with your body depends on multiple variables ... each of which will be unique to your physiology, the condition you are in on any given day (e.g. tiredness, hydration, cold, etc), the type of gas you were breathing, and the dive profile. For the most part, your body is designed to eliminate these bubbles through your lungs as you breathe ... but only within certain limits ... and not all of the bubbles will be making it to your lungs until your body tissues have reduced the level of nitrogen to more or less normal levels. That could take hours ... or even more than a day ... depending on the amount and type of diving you've been doing.

Some of what can occur in the meantime is that some of the bubbles can "stick" to the walls of your blood vessels ... much like they do to a glass of water left sitting on a table for a while. This creates a decrease in blood flow through those parts of your body. Blood clotting is also a common result of nitrogen buildup. Bubbles trapped in such a fashion won't get flushed to your lungs in a manner that's typically taught in scuba classes ... it's basically trapped, and can sometimes take more than a day to become "untrapped".

The problem with in-water recompression is that by reducing the size of bubbles trapped in the body you are allowing them to become untrapped and potentially migrate into smaller and smaller vessels ... where clotting or surface tension trapping them there can, when you surface and they regrow, result in blockages that cut off flow to vital parts of your body such as your brain or spinal cord. This is one of the major reasons why in-water recompression is not recommended except when there is no other alternative ... why it's considered a risky emergency procedure.

Your body is pretty robust, and for most recreational divers, the risk of DCS is less than other potential diver maladies like running out of air or neglecting to keep an open airway on an ascent. The best way to avoid all of that is to pay attention ... monitor your air supply and allow an adequate reserve for potential issues on the ascent. Once on the surface, remain there. If DCS symptoms occur, get on 100% oxygen as soon as possible, and remain on it until either the supply runs out or you can be transported to a hyperbaric facility. Do not re-enter the water. Beyond the risk I described above, if symptoms occur while underwater, you risk drowning ... which is never a preferable alternative to DCS.

Risk management is based on the notion that you don't trade off one potentially bad outcome for an even worse potentially bad outcome. DCS is usually fixable ... drowning is not. If you feel symptoms ... or even if you think you "might" be feeling symptoms (denial and typical bodily aches make it difficult to tell sometimes) ... don't go back into the water. All that would do is make the potential outcome even worse than it already is ...

... Bob (Grateful Diver)

bleeb:

OTOH, some if not all deco diving protocols include provisions for missed mandatory decompression stops when not showing symptoms.

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True, although deco diving protocols also call for using EANx or O2 at relatively high PPO2 and being accompanied by a safety diver who can get you to the surface if something bad happens.

VooDooGasMan:

debajo, on the first it all depends on if you were sucking up air fast and took in a bunch of nitrogen, and missed 20' foot stop, that also means you missed 10' stop. Instead of waiting an hour, change tank out and go down and complete deco, you could go to 35' and slowly ascend to deco. Memorizing the navy tables of the dive your doing will allow you to do deco as your computer would be locked out more than likely.

Click to expand...

How fast you breathe has nothing to do with how much nitrogen your body tissues absorb ... that is purely a function of pressure differences between the gas already in your body and the gas you are breathing ... in other words, it's determined by how deep you go, how fast you go there, and how long you remain. It's the PPN2 differential that determines absorption rate ... not how fast you breathe through your gas supply.



... Bob (Grateful Diver)

Yet If I take in very little air on descent to say 6 atm I have very little nitrogen narcosis, I have learned what you have put down there I am not sure this applys to everyone(me) as I have never been bent and I have done in water recompression when I thought I might be. Also I would say every body is different in absorbing, can't confirm just my thought on all the bent divers I have been around and the hyper treatment results.

The ? was missing a little deco and this does happen and divers have been fine, Debajo is wondering if it would help, can't really hurt.

Also is debajo bringing this ? to the table from other thread (GABI) where his friend asked if breathing 100% o2 @ 20' gonna help since hyper treatment is so expensive.

All people react differently to pressure underwater and for the most part out of 7 billion people on the planet, very few have been bent to conclude how each can take a hit.

Akimbo has some great knowledge that I have read on his experiences that have rang a bell or two, and hyp docs have only what works in the past.

debajo agua:

I know that there's risk involved with this scenario, but given safety factors that all no-deco algorithm use, how risky is it?

Click to expand...

You essentially asked one important question... the answer is it is extremely risky.

There are several factors that inform my answer... not the least of which, but perhaps the simplest to convey is: "Why on earth leave the relative security of the surface to undergo an ad-hoc procedure the parameters of which you know almost nothing about?"

The management of decompression is far more involved than jumping into the water, descending to 30 feet (9 metres) and spending 30 minutes there. You could, for example, do damage during your second ascent. You could, for example, risk CNS toxicity (either single dive or 24-hour limits), you could, for example, risk thermal stress, et al. In short, the best option by far... especially for an asymptomatic diver... is to breathe oxygen and super hydrate with fresh water while relaxing and staying warm and safe on the surface.

If you want to learn more about decompression theory and the protocols for in-water recompression, I suggest a little deeper research than a posting on ScubaBoard. As a starting point, why not invest in Mark Powell's excellent book: Deco for Divers. A search on Amazon will turn up ordering details.