Blow-n-go emergency ascent question

[Deac in the Wake]

Fantastic info; thanks folks. As always, the "it happened to me" stories are the ones that seem to stay foremost in the mind.

Like I said, this discussion is as close as I plan to ever get to DCS/DCI. I was struck by an author in a recent issue of Dive Training who said he was a research and lecturer on DCI and had never himself had it or dived with someone who had. Something poetic in that.

Thanks again.

 

[Dr Deco]

I would say that the researcher is cautious and keeps an eye on his buddies.

 

[Thalassamania]

I don't think the OP's question has been answered.

First let me make note that even if you drop your weightbelt, with a flare you can slow your ascent to under 60 FPM. So if you do so, you arrive at the surface inside of the No-D limits with a normal ascent and nothing more should be required (oxygen never hurts, so go ahead).

Now ... what if you had overstayed your no-D limits and surfaced (at less than 60 FPM)? Within 5 minutes of surfacing, if nonsymptomatic, "Omitted Decompression" protocols are available and re-immersion might well be the best plan. Oxygen rich deco mix would be a real plus.

If the diver surfaces and is symptomatic, that's a whole 'nother question ... but that was not the OP's question.

 

[Tom Winters]

Why would you drop the weight belt if you're properly weighted and not in a near-panic situation? If you recognize that you have just screwed up but you're still in control of things, start the emergency ascent.
If you're at 60' in a thick wetsuit, maybe a little overweighted with some air in your bc to compensate and you ditch the weight belt, you are not going to be able to control much of the event.
Here you have to do the best that you can - if at say 25', you're feeling like you're just not going to make it, well then you maybe have to pull/ditch the belt and hope for the best.
If you have a competent 'nother person in the water with you when you pop up and you're not twitching or glitching, go ahead and do a nice relaxed safety stop for a while. Some O2 back in the boat couldn't hurt either.
And if you do get bent, hit the chamber.
I've done OOAs from 80' and 60' decades apart from each other. They are not fun at all, but I kept the belt on both times. I would have ditched it in a second if I thought that I needed to.
Recently though, I went back down for a safety stop after I ran out of gas at the end of a long deco session.
I would have been better off skipping that - I had my wife throw her rig in do I could go back down. She dives a steel tank with a steel plate, so it's nice and negative. Plus the air was turned off. I had to swim 10' on the surface over to where she had dropped the rig and start chasing it down. I got it at 17' and counting when I stuck the reg in my mouth and got nothing.
I was at 20'+ when I got the damn valve turned on, and geez, did that stuff taste good. If her tank had been dry, that would have been it for me. You gotta just know when to leave that last lobster down there!
So watch the gas management stuff and keep the OOA stuff purely academic and discussed in bars, taverns, and public houses where OOB (out-of-booze) is the order of the day.
Hope that helps.

 

[lamont]

Assuming they have sufficient air, is there any benefit to getting their octo and descending to 15 feet for a safety stop?

Let's say you emergency ascend right next to the boat and another diver immediately gets with you as you surface. Should you proceed to exit onto the boat or is there anything gained by securing another air source and returning down the safety line/bar to 15 feet?

Recreational divers do not get sufficient gas loading to require IWR. All you've done is shift your *chances* of DCS from something like 1-in-10,000 to 1-in-100 or so. And if you do get DCS you're most likely to get subclinical DCS or a 'fatigue hit', you might get a type 1 hit and have joint pain, but you are unlikely to get type 2 DCS and neurological symptoms. There is almost no chance that any DCS from a recreational blow-and-go will be life-threatening.

The bigger problem is the recreational diver who doesn't really understand anything about DCS, doesn't have any IWR training, and often doesn't have a buddy with them, who descends to attempt IWR and in state of anxiety/panic manages to drown.

This also applies to recreational divers who 'pop' to the surface due to poor buoyancy control during or at the end of a dive. If the diver starts to panic over DCS and over their lack of control and winding up at the surface when they didn't mean to, that can easily start an accident chain. Its better at that point to take a deep breath, accept you screwed up a bit, accept that you might have some risk of mild DCS symptoms and to end the dive and get out of the water -- and chances are the worst symptom you're likely to get is taking a long nap on the ride home.

Also, attempts by OW divers to go back down for "missed decompression" may also simply cause shunting of bubbles and create a DCS problem that didn't exist before the IWR attempt. An OW diver coming up from a 100 foot dive who misses their deco stop, has bubbles form on the venous side of their circulatory system and then bounces back down for only a few minutes of a safety stop and then shoots back up to the surface may simply shunt bubbles and by attempting IWR may give themselves a case of type 2 DCS. Better to just stay on the surface, monitor and breathe O2 if symptoms develop.

 

[Thalassamania]

Recreational divers do not get sufficient gas loading to require IWR. All you've done is shift your *chances* of DCS from something like 1-in-10,000 to 1-in-100 or so. And if you do get DCS you're most likely to get subclinical DCS or a 'fatigue hit', you might get a type 1 hit and have joint pain, but you are unlikely to get type 2 DCS and neurological symptoms. There is almost no chance that any DCS from a recreational blow-and-go will be life-threatening.

The bigger problem is the recreational diver who doesn't really understand anything about DCS, doesn't have any IWR training, and often doesn't have a buddy with them, who descends to attempt IWR and in state of anxiety/panic manages to drown.

This also applies to recreational divers who 'pop' to the surface due to poor buoyancy control during or at the end of a dive. If the diver starts to panic over DCS and over their lack of control and winding up at the surface when they didn't mean to, that can easily start an accident chain. Its better at that point to take a deep breath, accept you screwed up a bit, accept that you might have some risk of mild DCS symptoms and to end the dive and get out of the water -- and chances are the worst symptom you're likely to get is taking a long nap on the ride home.

Also, attempts by OW divers to go back down for "missed decompression" may also simply cause shunting of bubbles and create a DCS problem that didn't exist before the IWR attempt. An OW diver coming up from a 100 foot dive who misses their deco stop, has bubbles form on the venous side of their circulatory system and then bounces back down for only a few minutes of a safety stop and then shoots back up to the surface may simply shunt bubbles and by attempting IWR may give themselves a case of type 2 DCS. Better to just stay on the surface, monitor and breathe O2 if symptoms develop.

Lamont, "Omitted Decompression" has nothing to do with bouncing, "back down for only a few minutes of a safety stop." Safety stops are obsolete and rather foolish in this day and age anyway. Omitted Decompression is just that ... a new schedule to make up for the fact that a diver did not make a REQUIRED decompression stop(s). Bubble pumping has not been shown to be an issue with this procedure, likely due to the increased stop time(s).

Here's the current recommendation of the U.S. Navy, as expressed by the NOAA Diving Office:

Should a diver realize that they have exceeded the nodecompression limits prior to reaching the surface, and they do not have access to USN decompression tables to determine required in-water deco time, they should:

• Stop at 10 to 15 fsw for a minimum of 15 minutes or until they reach 300 psi in their cylinder, which ever comes first.
• Once on the surface they should be placed on oxygen for a minimum of 30 minutes, observed, and restricted from diving for 12 hours.
• If symptoms occur during or after breathing oxygen for 30 minutes, they should be transported (on oxygen) to the nearest medical facility for treatment.

Should a diver not realize that they have exceeded the nodecompression limits prior to reaching the surface, or they have insufficient gas to perform in-water decompression, they should:

• Proceed to the surface at a normal rate of ascent
• Once on the surface they should notify the divemaster of their omitted decompression.
• If asymptomatic, and the diver can be returned safely to the water within 5 minutes after surfacing, they should dive to the depth of the missed decompression stops and remain for 1Ž½ times the required decompression stop time.
• If the diver cannot be returned to the water within 5 minutes, they should be placed on oxygen for a minimum of 60 minutes. If asymptomatic after breathing oxygen for 60 minutes, they should be observed for a minimum of 12 hours for signs and symptoms of DCS and restricted from diving during this observational period. If symptoms occur during or after breathing oxygen for 60 minutes, they should be transported (on oxygen) to the nearest medical facility for treatment.

Note: If a diver is asymptomatic and unable to return to the water to complete omitted decompression, and a recompression chamber is available within 1 hour travel, the diver should be transported to the chamber for possible treatment using USN TT5 or 6.