Help me to understand what happened

[jadairiii]

....switching gas just for shortening deco times looks unsafe and not worth the complexity and risk.......

The obvious concern is the diver's "fear" of switching gases, would just avoiding it is not fixing the problem. Someday he may have to switch gases for emergency reasons and be in a world of hurt.

And having done quite a few gas switches since my progression into Tech in '94, I can testify to the fact that there is no added "complexity" making it unsafe.

....Air is good. Air is safe......

I think this topic has been hashed out long ago.

 

[helodriver87]

I told you. I am old school...
And that is not "deep air".
Down to 60m is normal range for air. Deep air is BELOW 60m and down to 90m...

Well, again, modern definitions and all. Most people consider a 200ft air dive to be deep these days.

 

[happy-diver]

I unexpectedly silted myself out which was pretty stupid, the unexpected part, considering I was
diving a silted out wreck, and had just squeezed through an unsqueezable opening through silt.
Panicked for a few seconds with all vitals elevated, as I was telling that part of the brain to STFU.

So after diving all these decades, you just gotta deal with it, whatever comes new or old, done it
before done it not, experienced or not, as every dive is a new one like a buddy waiting to get you

Dive went off without a hitch

No buddy no team no body!


Better check my mask attached poorerlens and see if I can find the footage for any embellishment
You see the poorerlens is there to remember what my brain was doing during my embarrassments

 

[1atm]

Hi,

Group of us (6 recreational divers) did PSS Decompression procedures and PSS Accelerated decompression course this July. Two of us are sidemount divers that are feeling comfortable diving in SM configuration (50+ dives prior to tech course). Others are intermediate recreational divers that used tech configuration for the first time during course, so that fact made it more difficult for them.

We were doing our planned course dive which was 20 min. @ 40 meters with planned decompression using EAN 50 that we would switch to @ 21 meters.

When doing switch to EAN 50, one of the guys signaled that he has problems and is not ok. He went in a mild state of panic, but instructor managed to calm him down. Finally he made switch to EAN 50, did his decompression and finished the dive successfully.

At the debriefing he informed us that he felt convulsions when he switched to EAN 50 and couldn't breathe normally. We all assigned that to mild panic because he is a diver who is somehow pushing himself too hard and his skill level is not following.

Next day our planned dive was 20 minutes @ 50 meters using air in our doubles, and again EAN 50 for decompression.

When switching to EAN 50, he again signaled that he has problems, but now he wasn't panicking, just clearly signaling problem. Again, instructor managed to fix things and he finished his dive. At the debriefing, he basically told us story from day before. This time instructor stated that probable cause is bad stage regulator which could give him harder WOB. He gave him other regulator to try on next planned dive, which was shallow dive (15 m max) aimed only at practicing skills.

On that shallow dive, he managed to switch his regulator without any issue and everything was fine, but i am not satisfied with that solution because he was already practicing switching to stage regulator prior to first dive and using "bad" regulator and also everything went fine.

Anybody with similar experience? What could be other causes?

was he taking any medication? Sometimes there can be strange side effects or interactions between medications and high pO2. I know of some anecdotal evidence for instance of this happening with phenyl ephedrine (aka Sudafed, a drug that helps against swollen sinuses).

 

[KenGordon]

No one, as far as i remember, but himself. First dive prior to "real" deco dive was practice dive max. 20 meters where we were practicing switching from backgas to stage regulator which he did without any problem. Of course, on that dive he didn't have deco obligation.

Oh dear. Not very progressive.

90% he was, quite sensibly, shitting himself.

 

[Latenight]

was he taking any medication? Sometimes there can be strange side effects or interactions between medications and high pO2. I know of some anecdotal evidence for instance of this happening with phenyl ephedrine (aka Sudafed, a drug that helps against swollen sinuses).

No medications. After that incident, he event went to his phisician for a check, and to see if there is possibility that he is somehow sensitive to high ppO2, but that all came out negative.

 

[PfcAJ]

was he taking any medication? Sometimes there can be strange side effects or interactions between medications and high pO2. I know of some anecdotal evidence for instance of this happening with phenyl ephedrine (aka Sudafed, a drug that helps against swollen sinuses).

Phenylephrine and pseudoephedrine are not the same thing.


Iirc there is some limited support to the idea the taking pseudoephedrine can increase your oxygen toxicity risk. I am unaware of anything looking at phenylephrine.

 

[rddvet]

Phenylephrine and pseudoephedrine are not the same thing.


Iirc there is some limited support to the idea the taking pseudoephedrine can increase your oxygen toxicity risk. I am unaware of anything looking at phenylephrine.

that’s correct info. I had this conversation with DAN a year or two ago.

 

[beester]

just anxiety... too fast progression. The nasty thing is, this happens in a lot of courses, and the people earning their certs get out of the course not feeling comfortable. Having that itchy feeling that they are not yet ready for the dives they have now been certified for.

 

[beester]

My opinion, very old school.
I did hundredths of deco dives.
Down to 60m max.
All in air with doubles, and using back gas for deco. Sometimes also with a pony for added safety in caves, but also the pony with plain air.
Never used Nitrox. Never switched gas for deco. Never a problem.
I was not convinced on those theories about accelerated deco thanks to higher ppO2. Those theories are based on over-simplified models (such as Haldane or Bulhmann) of what happens inside our body.
Albeit these models were tuned so that they fit with large data series of dives without DCS (the same data series used for compiling the US Navy or the PADI deco tables) there is no proof that the same theories work well in the anomalous conditions of accelerated deco breathing highly oxygenated mixtures.
Personally I decided that these techniques involving gas switching are too advanced and too complex for me.
I have no problem doing a deco dive in air: I did always consider a dive planned just beyond NDL limits to be actually safer than a dive planned on the edge of NDL.
The deco dive will be done with more gas, with more redundant equipment and more strict procedures.
From this I scaled up to more serious dives where the limit is usually given by narchosis.And this can be done entirely in air, for example 20 min at 60 m.
Going further requires He mixtures.
Too much for me.
Making a dive to less than 60 m and switching gas just for shortening deco times looks unsafe and not worth the complexity and risk.
Air is good. Air is safe.
So I would warmly suggest to your colleague who suffered of problrms when switching gas, simply to avoid doing it again. There is no need to switch gas for deco when doing a dive in air at 40 or 50 m....

Heya, you are a scientist... so read up on some science on gas density (not even touching narcosis). Mmmm let me make it easy for you, watch below video. A presentation of Dr. Simon Mitchell, one of the foremost scientists working on scuba and rebreather related diving theory.


The density of air = 1.293g/L at 1 ATA, at 60 m it's above 9gr/L. All good if you are very relaxed and calm, but the moment you have a problem and your breathing rate increases you will be in trouble.

Finally, you must really like doing deco? The deco on air doubles to what you do if you switch to an efficient deco gas. It's not complicated, it's not dangerous.

Do agree with you that a dive just on the edge of NDL is potentially more dangerous than a real deco dive, specially if you "ride the NDL up". Meaning if you ascend just a bit when you reach NDL to gain 3-5 minutes, then when you reach NDL again ascend again just 3-5m and repeat..

I'm reacting not to you... in fact you do whatever you want. But advising other people with not so much experience that diving deep on air is safe... is irresponsible.

I'm a technical diver and instructor but also a CMAS instructor, and while I've done my share of deep air dives, and deco on air (in fact my CMAS card has an air depth limit of 90m). ... I would NEVER advice anybody to do deep air dives. There are just better ways.