Not diving to greater than 30m/100ft unless with helium

[1978davidw]

well scrubbing co2 out of the breathing air makes more of a difference than you might think.. Most shop air has between 200-400ppm C02. Our bodies discard C02 in the same way we absorb nitrogen by partial pressure gas exchange.. so at 150 feet for instance our bodies have to load to an equivalent of 1200-2400 ppm in order for c02 to be exchanged in the lungs. This in turn lowers the blood ph and causes the breathing rate to increase. i personally know of no one that has or does use a co2 scrubber in their compressor system except for me. I know once i changed my setup and added the scrubber my air consumption on deep dives went way down.i can easily do a 45 min dive at 100feet on a single steel 72 and always come back to the boat with close to 1kpsi. My dive buddy when i fill his tanks we have very similar profiles and when he uses one of our local shops he is always thumbing the dive for low air. I think this has a significant effect after experimenting with it.

 

[scubadada]

I've done about 225 of my dives to below 100 feet on air or nitrox. Only 13 have been below 130 feet, deep 161 feet. I understand narcosis is individual, for some of us, this nothing below 100 feet without helium makes no sense at all.

 

[wedivebc]

well scrubbing co2 out of the breathing air makes more of a difference than you might think.. Most shop air has between 200-400ppm C02. Our bodies discard C02 in the same way we absorb nitrogen by partial pressure gas exchange.. so at 150 feet for instance our bodies have to load to an equivalent of 1200-2400 ppm in order for c02 to be exchanged in the lungs. This in turn lowers the blood ph and causes the breathing rate to increase. i personally know of no one that has or does use a co2 scrubber in their compressor system except for me. I know once i changed my setup and added the scrubber my air consumption on deep dives went way down.i can easily do a 45 min dive at 100feet on a single steel 72 and always come back to the boat with close to 1kpsi. My dive buddy when i fill his tanks we have very similar profiles and when he uses one of our local shops he is always thumbing the dive for low air. I think this has a significant effect after experimenting with it.

I use a CO2 scrubbing system in my gas delivery system.

 

[Kevrumbo]

Has anyone here ever used CO2 scrubbers in their post compressor filtration system? I have my own compressor set up and i pack my own filters. right after my hopcalite which turns CO to CO2 i have a CO2 scrubber. This has helped a lot with headaches/narcosis as my CO2 levels are less than 10ppm in my air coming off my home compressor. For anyone doing deep dives i recomend this.

well scrubbing co2 out of the breathing air makes more of a difference than you might think.. Most shop air has between 200-400ppm C02. Our bodies discard C02 in the same way we absorb nitrogen by partial pressure gas exchange.. so at 150 feet for instance our bodies have to load to an equivalent of 1200-2400 ppm in order for c02 to be exchanged in the lungs. This in turn lowers the blood ph and causes the breathing rate to increase. i personally know of no one that has or does use a co2 scrubber in their compressor system except for me. I know once i changed my setup and added the scrubber my air consumption on deep dives went way down.i can easily do a 45 min dive at 100feet on a single steel 72 and always come back to the boat with close to 1kpsi. My dive buddy when i fill his tanks we have very similar profiles and when he uses one of our local shops he is always thumbing the dive for low air. I think this has a significant effect after experimenting with it.

Assuming a compliant and standard clean Air fill from a reputable Dive Shop, the actual problem is still with metabolic CO2 generation and physiological limitations of the human respiratory & circulatory system when it comes to Scuba in a immersed wet hyperbaric environment. Having a CO2 scrubbed and a hyper-filtered air source described above can't hurt, but doesn't really offer any practical advantage at all for work at deep depth. . . If you cannot expel metabolic CO2 efficiently because of physical exertion, or inadequate exhalation due to skip breathing, you will develop symptoms of Hypercapnia regardless of how well your source air has been scrubbed or filtered free of CO2 from your compressor.

Under normobaric and hyperbaric conditions, the single factor that limits the ability to increase ventilation is the rate at which gas can be exhaled from the lungs. The ability to exhale gas is reduced during hyperbaric and diving conditions. As gas density increases [with deeper depth], increased effort is required to exhale gas (i.e.,it takes more work to move a heavier gas).
Article: Carbon Dioxide, Narcosis and Diving.
https://www.globalunderwaterexplorers.org/carbon-dioxide-narcosis-and-diving

The point is: You can have an ultra-scrubbed & hyper-filtered air fill source devoid of CO2 at 10ppm, but even that benefit will be swamped-out by the body's own metabolic CO2 production at depth with extreme physical exertion and resulting Hypercapnia, brought on by the increased gas density of air and work-of-breathing. . .

"

Originally Posted by TSandM Overbreathing the regulator MEANS a CO2 hit . . . It means the increased work of breathing of using a regulator is enough, at the current demand, to prevent you from exhausting all your CO2. All regulators can deliver more gas, faster than you can use up oxygen, but the small increase in resistance involved in trigger the inlet valve and opening the exhaust valve can make the difference between being able to keep your CO2 normal under heavy work loads, and not being able to keep up. Panic in the experienced diver?

Originally Posted by TSandM CO2 in the bloodstream is completely determined by minute ventilation, assuming the gas you are breathing does not contain additional CO2. Bailing to open circuit definitely makes it POSSIBLE to reduce the blood CO2 level, assuming you can achieve a higher minute ventilation than what's required to keep the CO2 where it is (which is in part related to level of exertion). It may not, however, be possible to reduce CO2 fast enough to clear your head and get rid of the panicky feeling, in part because the natural tendency when panicky is to breathe as fast as possible. On scuba, this means reducing the efficiency of the ventilation, because too much of it is just going to exchange gas in the trachea and large bronchi, which don't exchange gas. That's why we are taught in OW that, if we begin to "overbreathe our regulator" (meaning the diver feels short of breath despite breathing as much as he can), we are to STOP, hang onto something (reduce exertion) and breathe SLOWLY and DEEPLY. It is then possible to reduce CO2. What may not be possible is to stay rational long enough to do it. Panic in the experienced diver?

 

[Akimbo]

The point is: You can have an ultra-scrubbed & hyper-filtered air fill source devoid of CO2 at 10ppm, but even that benefit will be swamped-out by the body's metabolic CO2 production at depth with extreme physical exertion, caused by the increased gas density of air and work-of-breathing.

Agreed, in fact you don't have to go that far. Normal execration for a diver at 66+' on air/Nitrox swamps the 200-400ppm CO2 in a normal fill. You can't blame it all on the regulator either. Most people notice substantial increased breathing resistance at 50M/165'/6 ATA in a dry chamber. I have had chamber newbies tell me it was like breathing whipped cream. Obviously an exaggeration but it is significant.

It is much harder to notice the density with all the distractions underwater, and then it is easy to blame it on the regulator.

 

[MXGratefulDiver]

I've done about 225 of my dives to below 100 feet on air or nitrox. Only 13 have been below 130 feet, deep 161 feet. I understand narcosis is individual, for some of us, this nothing below 100 feet without helium makes no sense at all.

For you, perhaps. It varies from person to person, but I think it makes sense for some people. I draw my personal line at 120 fsw ... below that I tend to get out of my comfort zone without some helium in my mix ... and that's just not a place I want to be underwater ...

... Bob (Grateful Diver)

 

[Rooster59]

This article was very sad to read, but it did have some information that really made me think about scuba and depth:

Diver deaths result in changes to Navy Dive Manual, equipment | WTKR.com

 

[Akimbo]

This article was very sad to read, but it did have some information that really made me think about scuba and depth:

Diver deaths result in changes to Navy Dive Manual, equipment | WTKR.com

The manual change was to specifically state that "there is no such thing as an operational necessity in training" -- which was used to argue that it was OK for them to exceed the 130' Scuba limit for this dive. It should be noted that Trimix would not have made this dive "within operational limits" either.

Here is a Scubaboard thread on the dive: http://www.scubaboard.com/forums/ac...s-1-year-ago-finally-released-under-foia.html

 

[Kevrumbo]

Another example of the insidious and overwhelming nature of CO2 Retention with a novice diver at depth:

. . .. The ER Doctor who treated me was a former dive instructor and I explained what occurred. I learned that because of my panic and task loading I was was over breathing my regulator and breathing back the CO2 I was exhaling which was displacing oxygen. This gave me the sensation of “not having air”. After getting released, I left the ER and called it a day. I was so disappointed with myself I really thought I was going to walk away from diving for good.

In hindsight, there was so many errors with this dive starting from poor planning and lack of discussion about the dive site to lack of enough training on handling issues. I was very fortunate that I didn’t end up getting bent or worse drowning due to errors that were made. Its true what they say about “What doesn’t kill you… “ I did gain much insight from the experience but definitely would have rather read this on Scubaboard.com if it had existed back then.. ha!..

Thanks for reading.

http://www.scubaboard.com/forums/near-misses-and-lessons-learned/516915-my-lesson-learned.html

And so again, any planned overhead diving requiring a clear head or expected physical exertion at deep depth, should be utilizing the narcosis mitigating benefits of Helium.

Unfortunately with the high price of He these days (and getting Trimix trained & certified as well), it's a tough cost versus risk decision with many divers choosing to take the risk of breathing Air or Nitrox instead.

 

[Akimbo]

... Unfortunately with the high price of He these days (and getting Trimix trained & certified as well), it's a tough cost versus risk decision with many divers choosing to take the risk of breathing Air or Nitrox instead.

Or eliminate the risk entirely and just don't go there. It's not like recreational divers (which includes the vast majority of technical divers) are being paid or have a job to do.

There's always something deeper we "would like to see", but there is nothing that we "need" to see. "Would like to see" isn't worth exceeding your limits to have a little fun. Find, set, and stick by your limits. Sure there is a gray area, but that is why you need to slowly and carefully find your limits over time rather than just arbitrarily accepting some else's.