Nitrox vs. Regular Air?

[mempilot]

I have never liked this silly 'coined' term Triox.

Agree. There is air. There is nitrox. And, there is trimix. You could argue heliox, but really they are all flavors of the core three.

 

[Age]

All the NAUI books are metric-enabled. In fact, they usually write things like, "...still for actual depths from 21 meters (70 feet) to 33 meters (110 feet),..." (p. 55). Examples may be in "U.S./Imperial", but they are usually accompanied by metric examples (or "The procedure is identical in an S.I./metric calculation." for some that are trivial). All the charts are either multi-system (dive tables) or in pairs (figure 4-1a in fsw, with figure 4-1b in msw right below).

(They're called "NAUI Worldwide", so it'd be a crying shame if we couldn't work in meters and bars. On second thought, forget the meters. )
Well, I seem to be flat out of firstborn, for one.

The materials arrived today and as you say, they have metric and Imperial examples and the tables are "bilingual" too. But then I spotted, something I had never seen before; an Oxygen Calculator for EAN. Cool, I thought, I won't need a calculator when the PPO2 reads 33.7%. Then I looked closer, sure enough it was in fsw not msw and I was informed that I have to divide by 3.28 to make it something I can understand. Worldwide, my foot! Still, I have to say that what I've read so far is very informative. I had no idea about the history of Nitrox.

 

[espenskogen]

Recreationally speaking, you are wrong. Run a 120 fsw dive for with 15 minutes of bottom time utilizing ean30 and then trimix 30/10. The END for ean30 is 103, and the END for 30/10 is 83. The NDL is the same, but the narcosis level is 20 feet less. What you speak of comes from He ongassing quickly and offgassing quickly. On decompression dives this is important with much longer and deeper dives, but for recreational dives, it isn't. The only big thing to remember when diving recreational trimix vs nitrox is to utilize a very slow ascent rate, which you should be anyways.

I don't agree with using Trimix for Recreational diving. Narcosis is not a significant problem at depths of 40 meters or less, and if you dive deeper than 40 meters, then it's per definition a tech dive (or a stupid dive, should you try to do it with a single cylinder and no deco). You increase the bend risk significantly by mixing helium into your mix, and should you get a hit, it's likely to be more severe. Sounds like a great idea for the average recreational diver, doesn't it?

Trimix is an extension of nitrox and solves the remaining problem, narcosis. I didn't mix it into the NDL discussion, but merely made an insignificant comment. But thank you for allowing me to show your ignorance on the subject since you would like to expand on the conversation. BTW, Recreational Trimix is a course and is aimed at NDL diving. I'm starting to wonder what level of diving you actual do? You sound like the antagonists of nitrox back in the day.

Trimix does solve narcosis, but narcosis is not a problem within recreational diving limits. There are a number of courses aimed at NDL diving which makes little sense. Recreational Trimix is just one of them. Normoxic trimix does make some sense, but that is aimed for tech diving with a depth limit of 65m, which is still anything but recreational.
So you wonder what kind of diving I do? Not recreational diving on Trimix, that's for sure. The antagonists of Nitrox back in the day said don't use the voodoo gas, you're all going to die!!

I'm saying use the right gas for the job. If you are diving deep enough for narcosis to be an issue, then by all means use trimix. But if you are a recreational diver doing 20 - 30 meter dives, the question is whether to use nitrox 21, 32 or 36. The operative word here is risk management. You use Trimix on deep tech dives because on these dives, the risk of not using Trimix is higher than the risk of using it. Trimix in itself is no goal.

I never said anything about extending NDL by using trimix. Where did you get that from? I said trimix has all the benefits of nitrox without the narcosis. You obviously have a hard time understanding a simple sentence like that. Go get some education on the matter.

The discussion in this thread was related to the benefits of nitrox which is to either reduce the bend risk by reducing the amount of inert gas in your system, or to increase the bottom time by reducing the amount of inert gas in the mix. One can only assume that you'd actually read the thread, and not just threw out a comment about how one should forget about Nitrox, because Trimix is the Rage. Now bare in mind that a considerable amount of recreational divers suffer from questionable buoyancy control - What would the benefit to them be by adding helium in the mix? Not a great deal, I can assure you. As for my education - This might be news to you, but most peoples perception of offensive ba****ds like you is that you might be the one lacking in education. Besides, it's not me who's got the following fitness challenge on his profile: Trying to get past 3rd grade reading level.: ) and counting...

 

[Age]

a little bit off-topic here, but: could someone please explain to me why nitrox is not optimal past 100 feet (or another number close, like 110 feet). i see people always mentioning that you shouldn't use it once you go past a certain depth. why not? and what would you want to use instead? trimix?

You are not off topic at all, but these guys are into serious debate right now, so I'll try and answer. I'm sure somebody will correct me if I'm wrong. Here goes:

Strangely enough O2 is toxic to all living things. If you breath it at 100% at the surface for more than 5 hours you'll start to damage your lungs. Think what it does to a bicycle or a fine wine given enough exposure. It's a destructive force. However, we have evolved to tolerate this toxic substance that gives us life at a PPO2 of .21. That means the 21% of O2 in the air that we breath at sea level. Climb a mountain this reduces (but that's another story) PP means partial pressure and as you descend the PP of O2 increases. However, empirical evidence shows that if the Partial Pressure of O2 reaches about 1.6, there is a strong possibility of Oxygen Toxicity, which causes convulsions and may therefore cause you to spit your regulator out and you will die unless your buddy can save you by keeping your regulator in your mouth and taking to a shallower depth.

For example, if your mix is 32 % O2 then your PPO2 would be 1.6 at 40 metres. Obviously, you wouldn't want to go anywhere near there, so most agencies consider a safety margin of .2 i.e 1.4 PPO2 to be acceptable. That would mean you would limit your maximum depth to 33 metres. Hope this helps, but bear in mind that there are 100+ pages books on the subject and you need to research further. Indeed, so do I.

 

[Blackwood]

You increase the bend risk significantly by mixing helium into your mix, and should you get a hit, it's likely to be more severe. Sounds like a great idea for the average recreational diver, doesn't it?

That's debatable. When helium deco tables first came out, they penalized it because it is light. However since Helium isn't very soluble in our tissues, it's not really a problem.

Trimix does solve narcosis, but narcosis is not a problem within recreational diving limits.

I've been narced enough in cold water at 90-100 feet that I couldn't swim in a straight line (midwater no visual references).

 

[espenskogen]

That's debatable. When helium deco tables first came out, they penalized it because it is light. However since Helium isn't very soluble in our tissues, it's not really a problem.

Maybe so, I'm not an expert on the physiology. In the TDI training I did, the mantra was 'A fast ascent on air and you'll hurt. On Trimix, you will almost certainly die' - Now of course this applied primarily to missed deco and fast ascent, but the point was that Helium is less tolerant to rapid ascents because it bubbles quicker. This would be because it comes out of solution quicker. Blood is also a tissue in terms of the deco obligations, which has similar characteristics to water - We've all seen the coke bottle example, and helium fizzes more than CO2, so you make up your own mind..

I've been narced enough in cold water at 90-100 feet that I couldn't swim in a straight line (midwater no visual references).

Hey, I'm diving in the UK, so know where you're coming from. Midwater free ascents in strong current, bugger all visibility and cold water can be really sucky sometimes... - However, although narcosis can be noticed at 30 m (100ft), it is nowhere near as debilitating as it is on 50 -60 meters, and the impairment at 30 meters don't warrant the increased risk of helium in my opinion. (And certainly not for a type of diving, where the majority of participants have less than 20 dives a year, and less than brilliant buoyancy control)

There are those that argue that narcosis is narcosis, and it's defined by the pressure rather than the environment (dark/poor viz etc), and that the environment just sets the parameters for how it's experienced. I'm on the fence on this one, but it's one point of view. Having said that, I'm happy doing 45 m on air in the UK, but 60m on air in the Red Sea, so I guess the experience is the important thing, not the physiological level of impairment as a result of the narcosis.
Each to their own on this one though - If a diver chooses trimix for a recreational dive it's their business. Just don't think its ever going to be a Nitrox killer - Solves different problems, as mentioned earlier.

 

[Blackwood]

Maybe so, I'm not an expert on the physiology. In the TDI training I did, the mantra was 'A fast ascent on air and you'll hurt. On Trimix, you will almost certainly die' - Now of course this applied primarily to missed deco and fast ascent, but the point was that Helium is less tolerant to rapid ascents because it bubbles quicker. This would be because it comes out of solution quicker.

Yah. That has been re-thought by some. If it isn't soluble, it doesn't go into solution. If it doesn't go into solution, it doesn't have to come out of solution. Breathe in, breathe out.

That said, any gas we breathe under pressure can bend us. Due to the solubility and metabolic properties of oxygen, we tend to treat it as not contributing to DCS. But if it were possible to suck on pure oxygen at 150 feet for an hour, it could bend us. So can nitrogen and helium.

Anyway, as you said, what to believe is up to the individual. Personally, I won't penalize myself for breathing helium.

Hey, I'm diving in the UK, so know where you're coming from. Midwater free ascents in strong current, bugger all visibility and cold water can be really sucky sometimes... - However, although narcosis can be noticed at 30 m (100ft), it is nowhere near as debilitating as it is on 50 -60 meters

In the same water, sure. Narced at 30, more narced at 50.

But many people will operate better at 50 meters in the Red Sea or French Polynesia than they will at 30 meters in cold murky Redondo or UK waters. And, of course, it varies from dive to dive.

I tend to agree that for many recreational dives helium is overkill. However, it may sometimes have merit.

And there is more to it than risk. This is an anecdote that my trimix instructor passed along. Two divers (I can't remember their names) dove the same wreck for years on air. One day, they were convinced to try mix (pun intended ). After the dive, they came up talking about all these things they saw that they had never noticed or remembered before. Portholes, railings, etc.. On a wreck they'd hit a hundred times!

Risk be darned, I dive to see the underwater world. But If I can't remember it, what was point?

Would I dive mix to 90 feet? No. 110? Maybe. Am I penetrating?

 

[RJP]

The owner of one of the shops in town won't even let his employees dive with regular air unless they are just going to be in a pool training.

I guess he also limits the depths of their dives as well?

 

[ianr33]

empirical evidence shows that if the Partial Pressure of O2 reaches about 1.6, there is a strong possibility of Oxygen Toxicity, which causes convulsions and may therefore cause you to spit your regulator out and you will die unless your buddy can save you by keeping your regulator in your mouth and taking to a shallower depth.

Actually it is not recommended to ascend with a toxing diver. During the seizure the airway will be closed so ascending will cause lung damage/ AGE as the expanding gas has nowhere to go. The preferred method is to stay with the diver until the seizure stops and then ascend.
As far as I know there has only been a handful of successful rescues of divers having O2 convulsions. Much better never to get into that situation in the first place.

 

[texdiveguy]

But if it were possible to suck on pure oxygen at 150 feet for an hour, it could bend us.

.....that would be the least of your worries.