stupid question

[divebag]

If a diver ascends too quickly or enters deco by staying at depth too long and doesn't realize it until surfacing, why couldn't you just get back in water and descend to 15 to 30 feet and and to a prolonged safety stop or deco stop as long as sufficient air was available. Wouldn't that help reduce the risk of DCI?

 

[LUBOLD8431]

You could...

Its called inwater decompression, or ommitted deco procedure. It will help, sometimes. It depends how much deco the person blew off. Obviously, if a technical diver blew off over an hour or more of deco, did a polaris ascent, it isnt going to help him very much (he is most likely toast).
If a recreational diver omits a deco obligation based on what their computer is telling them (yes, I am assuming some things here), then yes, it would help...

Fast ascents are something that need to be avoided. Going back down and staying there for a safety stop is not going to have a significant effect on an embolism. If someone has symptoms of an air embolism after a fast ascent, they need to go to a chamber asap.

 

[divebag]

The above question is predicated that there were no obvisous symtpoms of DCI upon surfacing, yet.

 

[SeaCobra]

If you are on the boat and alive, stay that way. As far as recreational diving goes, if you miss a deco stop, get on the boat (or whatever), breathe O2 and monitor for signs of DCS.

If symptoms occur, then you know the drill.

 

[Padipro]

Another good reason a recreational diver should not get back into the water for a missed deco is gas supply. If you've been down long enough to incure a deco obligation then most likely you are nearly out of gas and unless you have good surface support to send tanks down to you at your stop depth chances are you'll run out of gas before you finish your deco. Most recreational dive boats do not have the kind of support that is needed to do this and trying would, most likely, only make things worse.

Another reason not to do in water recompression is if a diver should loose consciousness due to DCS, again unless you have good support from other divers on board, you would likely drown.

As others have said it's better to stay on board and watch for symptoms.

 

[DA Aquamaster]

PADI had an omitted decompression procedure in the mid 80's when I took my AOW course. It assumes a maximum surface interval of 5 minutes, no symptoms of DCS and specifies stop depths of:

40 feet for 1/4 of the 10 ft stop time
30 feet for 1/3 of the 10 ft stop time
20 feet for 1/2 of the 10 ft stop time
10 feet for 1 1/2 of the 10 ft stop time

The procedure was obviously self limiting as if a 20' stop was required the procedure was not valid any longer. I think in more extreme cases with large amounts of missed deco, it is far less likely you will be symptom free after surfacing and going down again would just make things worse so is not an option. In that situation you are far better off staying on the boat waiting for evacation to a chamber and breathing 02 if it is available.

Oxygen was not normally on dive boats at the time so an in water procedure was the only option other than hoping and praying. The more likely possibility today of having oxygen on the boat would present you with the option of staying on the boat and breathing 100% O2.

But in my case the local chamber is a plastic tube good to only 60' and will not be much help in treating a case of DCS. Given that it would take several hours to get me to the nearest chamber capable of adequate treatment, I would opt for the missed deco procedure using Nitrox 50 or Nitrox 80 in the water followed by 100% 02 on the boat.

On my boat during deep dives the nitrox is suspended at 20 ft below the boat and rigged as a stage bottle. It prevents a diver from having to surface and miss the deco in the first place, assuming they can navigate back to the anchor line. Alternatively it also reduces the surface interval for a diver who may surface away from the boat as all they have to do is return to the boat and if symptom free decend and clip on the tank and continue to 40 ft. for the first stop.

In practice a diver has to be really clueless to just forget that he has a deco obligation. It is more likely to be missed due to poor gas management on the part of the clueless diver and that is also preventable with proper planning and technique.

 

[iainwilliams]

Breathing 100% O2 at 6 meters would also help considerably as the O2 creates a pressure differencial between the N2 and O2 elliminating N2 far faster than without O2. Oxygen toxcity would need to be considered.

This actually happened on a dive trip a few years ago - not to me but to another diver. He dived to 18 m for 65 minutes and bolted to the surface (accidently). Upon surfacing he felt very tired and his arms ached. We decended him back to 5 m on 100% O2 for a period of time slowing working him to the surface. Safety divers were always present and as it occurred in a remote area of Papua Nui Guinea, hypthermia was not an issue.

He felt 100% on surfacing and did not attend a chamber - nor did he dive for the remainder of the trip.

Note that this was on dive trip that was very remote away from any form of transport and emergency evacuation. ....Iain

 

[fins wake]

Breathing 100% O2 at 6 meters would also help considerably as the O2 creates a pressure differencial between the N2 and O2 elliminating N2 far faster than without O2. Oxygen toxcity would need to be considered.

While breathing pure oxygen at a shallow decompression stop is a regular event for technical divers, this is not recommended procedure for recreational divers. Oxygen toxicity is a very real risk and many recreational divers who read this board cannot be expected to have the training or skills to handle hyperbaric oxygen in the water. Indeed, a diver who ascends to quickly or overstays his time at depth only realizing this upon surfacing (as in the actual example given) could certainly not be trusted to automatically handle omitted decompression procedures on pure oxygen.

The earlier advice, to stay on-board the dive boat, breathe oxygen and monitor for symptoms is the best. Emergency IWR upon the onset on symptoms (whether on oxygen or not) at very distant dive sites (such as PNG) fall out of the general realm for this particular thread.

Incidentally, there's a slight mixing up of the effect of descending to depth (forcing nitrogen or other inert gases back into the tissues) and the effect of oxygen on off-gassing in your first paragraph. There's an interesting discussion on this right now at The Deco Stop. The point being that many recreational divers with minor decompression obligations due to overstaying their time at depth by a small degree or by somewhat fast ascent rates would benefit from surface oxygen without risk of CNS toxicity.

Also, the PADI recreational emergency decompression procedures listed on the RDP are very useful. The interested reader can compare the stop times at 5 metres here with similar times spent at depth on Bühlmann, DCIEM or BSAC tables.

 

[WaterDawg]

I ran into a situation that required us to back down to about 15 ft for 1/2 hr this weekend. I belive that if you have the gas (hopefully higer o2 than air) and you didnt have any symptoms you should do it. I belive it saved us.