Going back down to stop deco

[knobber]

sorry, this has surely been asked before. However, I'm getting frustrated at not getting an answer, so I'm going to try here.

WHY are you not allowed to go back down to decompress if you know you came up too fast and will most likely get bent? I asked that in my open water class and the answer was "noooooo, never never never never go back down", and that was it. The books say "never go back down to stop decompression". The DAN medical book I just got says it can only be done with highly trained professionals. It just seems the normal thing to do, and I can't figure out the physiological reason not to.

Let's say I'm 80 miles offshore swimming a rig with a buddy, came up fast for some strange reason from 70, 80 degree water, and had plenty of air in my tank leftover. Why couldn't I go back down to 60 and slowly return?

thanks for all the help so far guys!

 

[rmediver2002]

Most agencies are recommending only no decompression SCUBA diving, there would be no real advantage to swimming back down to depth and coming up slower, or for that matter going back down to complete a non-required stop (safety stop) on a no decompression dive.

Of course the diver should be observed closely on the surface as the chance of developing some symptom tentially related to pulmonary over-inflation is greatly increased...

Jeff Lane

 

[HammerNoMore]

knobber once bubbled...
WHY are you not allowed to go back down to decompress if you know you came up too fast and will most likely get bent? I asked that in my open water class and the answer was "noooooo, never never never never go back down", and that was it. The books say "never go back down to stop decompression". The DAN medical book I just got says it can only be done with highly trained professionals. It just seems the normal thing to do, and I can't figure out the physiological reason not to.

Let's say I'm 80 miles offshore swimming a rig with a buddy, came up fast for some strange reason from 70, 80 degree water, and had plenty of air in my tank leftover. Why couldn't I go back down to 60 and slowly return?

thanks for all the help so far guys!

There are two issues here. One is the completion of a missed deco stop in the case where DCI has not (or not yet) occured. You are asking in the wrong places in your open water class. Open water training is all about non-deco diving so asking questions about missed deco stops is not likely to get a real answer.

Say in your example that your buddy passed out at depth and was not breathing, but you have a mandatory deco stop. You have the choice of not helping your buddy because it would put you in danger. If you do decide to help your buddy to the surface do you jump out and grab the 02 for yourself or do you let the boat crew deal with your buddy and immediatly resubmerge and complete your deco? Personally, I would complete the deco.

The other issue is what to do when you have DCI symptoms. Most people do not recomend in water recompression. This is because it delays professional treatment and it would be very difficult to duplicate the recompression you would get in a chamber. Also, in most cases you would be recompessing on air, instead of 02.

Read http://www.daneurope.org/eng/iwr.pdf for information on actual case studies of IWR. This is not a DAN article but I do find it fascenating that DAN europe has it posted on their website. Makes me wonder if DAN is reconsidering their position on IWR.

 

[DA Aquamaster]

In the early 80's when I got my PADI AOW training deco diving was covered and procedures for omitted deco were actually taught.

Assuming a surface interval of less than 5 minutes and no signs of DCS, the PADI "Special Procedure" for omitted deco called for a 40 ft stop for 1/4 of the 10 ft stop time, 30 ft for 1/3 the 10 ft stop time, 20 ft for 1/2 the 10 ft stop time and 10 ft for 1 1/2 the 10 ft stop time.

In water recompression with signs of DCS is another matter entirely. It is workable only if you have access to adequate 02 (normally surface supplied), a full face mask, a saftey diver who can moniter you and a bar to sit or hang off during the long schedule and slow ascent rates involved. Most in water recompression procedures are long (90 minutes or so) and require very slow ascent rates that essentially require a bar to sit hang on while you are slowly hauled up at the specified rate.

In my opinion it would be worth doing only if you have all the required elements in place, are not able to get to a chamber for a considerable period of time, and are not in water too cold to preclude a 90 minute dive while you sit and do nothing.

In water recompression is limited in the depths and pressures that are practical (30-60ft.) You are not going to be able to go to 165 for a table 5 schedule and you are not going to be able to use the same high PO2's and air breaks you would get in a chamber. The way bubble mechanics work, you have to go substantially deeper than where the bubble formed to get the bubble to even reduce its size by half and getting it back into solution entirely is not going to happen. Depending on the situation, the pressure available for IWR may not be adequate and in some case you may just be aggravating an already bad situation and further delaying treatment.

It could have applications on an expedition type dive in the middle of the nowhere, but in that case it would be smarter to plan for the eventuallity and bring along one of the newer lightweight recompression chambers.

In a recreational situation where the NDL were unintentionally exceeded, the stop missed and no signs of DCS are present I would personally consider the old PADI procedure, but I would follow it up with 100% O2 on the boat for at least half an hour. That is however not to say I would recommend it for anyone else - it is a dated procedure.

Current treatment calls for 100% 02 administration at the surface for a suspected case of DCS while on your way to a medical facility. 100% O2 by itself can in many slightly over the edge cases prevent the onset of DCS, and in a few cases 100% O2 at the surface can resolve minor DCS symptoms. In the event that occurred, I would still continue on the way to the ER and still consult with a physician trained in diving medicine for possible treatment.

 

[rmediver2002]

I did not realize PADI ever taught that DA, it looks like a modification of the Navy ommitted Decompression procedures but I would personally advise against traveling to 40 fsw for your first stop unless the first stop missed was 30 fsw...

Good description of the procedure DA, especially making the distinction apparent between ommitted decompression and attempts at in water treatment (two very different animals here)... There are several out there but I would like to stress your comment about the availablity of a recompression chamber, the common recommendation is if the chamber is more than 12 hours away then consider attempting inwater treatment.

In almost any case in this day and age it would be better to transport on 100% O2 to the nearest chamber...

Jeff Lane

 

[Dr Deco]

Dear Scuba Board Readers:

Omitted Decompression

As has been mentioned many times in the FORUM, the dive table are designed in such a fashion that a considerable margin of safety exists for most divers. For a few, that margin will be very large, and for another few at the opposite end of the bell-shaped curve, that margin will be smaller. There does not exist a "bends"/ “no-bends" line. Thus, unless you definitely have a DCS problem, I would not really see the need for reentering the water for decompression at the ten-foot stop.

Deeper stops will be another question. There is not any way to tell whether you are a resistant diver or a sensitive diver, and, as responders have indicated above, completion of decompression is certainly a wise consideration.

In-Water Recompression

In reading the report for DAN in Europe, it is definitely possible to see all types of responses. I must say that, when working with animal test subjects, the individual responses are “all over the map” and good conclusions about any one animal are difficult to make. I can add a few comments, however.

• The 165-foot depth was added to the Table 5 [I ] because it already existed in the US Navy. [/I] The researchers found that bubbles passed through tissues and into the venous system at about 100 fsw, but it would require a rewriting of Navy regulations to go to 100 fsw whereas 165 was already a procedure (air treatment).
• The old air treatment tables were replaced with the oxygen table because the air tables failed so often. Air is not really a good gas for treatment of DCS.
• Gas bubbles cause neurological problems by blockage of blood vessels are not round, they are cylindrical. The doubling of pressure reduces the length by one half. A point is reached where the bubbles will eventually be forced through the capillary by the arterial blood pressure (so-called “stick/slip dynamics”)

DCS Process

My comments are those of a research scientist based on physiology. I also follow the results from the field to see how this is playing out.

Dr Deco :doctor:

 

[RichLockyer]

knobber once bubbled...
Let's say I'm 80 miles offshore swimming a rig with a buddy, came up fast for some strange reason from 70, 80 degree water, and had plenty of air in my tank leftover. Why couldn't I go back down to 60 and slowly return?

http://www.wkpp.org/articles/Decompression/why_we_do_not_bounce_dive_after_diving.htm

In short, you can re-descend, but treat it as a repetitive dive and "stay down long enough for everything to reset" (30 minutes?)... don't consider it as "treatment".
You probably aren't going to be able to do that on a single tank unless the ascent was at the beginning of the dive, and in that case, you aren't likely to have enough N2 load to bend you in the first place.

Best thing is to play it safe and keep the surface interval to at least an hour.

As far as the concern over a fast ascent or missed safety stop... how fast? How deep for how long... "mandatory" or not safety stop?
For many years divers did direct ascents at 60fpm and the "hit rate" was acceptably low. Safety has been improved though rate reductions to 30fpm and the safety stop, but that is merely a safety enhancement. A 120fpm ascent rate would be unlikely to bend you from a conservative, shallow rec dive.

 

[knobber]

so it sounds like it isn't as taboo as I was led to believe, but only if you show the signs of DCS and only if you have the air to do it correctly. Not that I want to try it; it just seems weird that if you're out in the middle of no where it's more "logical" to call air transport in when you could seemingly just go down and recompress like the caisson workers did. thanks for the explanations--and hopefully I'll never have to find out!

 

[rmediver2002]

so it sounds like it isn't as taboo as I was led to believe, but only if you show the signs of DCS and only if you have the air to do it correctly

No man, if you have sign of decompression sickness soon after surfacing then it would be a bad idea to go in the water to complete decompression.

At this point it if you went in at all it would be to conduct an in water treatment protocol, and that would not make much sense when you have access to a recompression chamber and medical personnel trained in treatment of diving injuries.

The middle of no-where is being more than 12 hours from the nearest facility...

Jeff Lane

 

[fins wake]

Omitted decompression stops and the like are actually considered by all technical and deeper OW training agencies, but the responses vary widely. I believe the BSAC approach is "never go back down" whereas the contemporary DSAT (PADI TecRec) approach is very rigorous and based on differing time-scales (and yes, you're supposed to know all this by heart to gain the certificate.)

PADI's main - recreational - branch and other recreational agencies certainly don't even mention omitted decompression stops, as everybody has pointed out. You do not do compulsory decompression diving - ever - with the (U.S.) recreational agencies.

As for IWR, it's a highly controversial subject. There were quite a few people - including myself - at a dive medical course I attended who wanted to get some advice on IWR from the medical experts, just the way you do in this thread.

None of the doctors would commit to a firm answer. The basic line was "if you're in Sweden or the Western world or close to a recompression chamber, never go back down. If you're in Papua New Guinea on an expedition, well ..."

There are plenty of opinions on IWR, and indeed some studies, particularly in Australia ( = big distances from civilization). I would recommend you have a look at the standard textbooks by Edmonds et al, and by Bennet & Elliot. There is also quite a lot of information if you google the web.

But the basic line is that in 99% of cases, you'll put the victim or anybody suspected of e.g. omitting stops and likely to get bent on pure oxygen as soon as possible, monitor for symptoms, phone DAN, the Coast Guard or the Navy (depending on country) and prepare for evacuation to the nearest recompression chamber.

You do not put clearly afflicted divers back into the water. The US Navy protocol is too difficult to administer by laymen and without proper equipment, the Australian protocol likewise. That said, there is anecdotal evidence of people whose lives may have been saved even by imperfect IWR. But it's a controversial subject.

(BTW, legal niceties in the U.S, the UK and some other countries may preclude the automatic administering of oxygen, which is both a scandal and a tragedy, so please be aware of these legal niceties. But personally I'd go for the O2 bottle all the same ... First time, every time when there's a high likelihood of DCI.)