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I haven't read all of the posts so please forgive me if I repeat something that is already mentioned. Does the brand of reg you have make diving safer? Does the brand of BC you dive make diving safer? Unless you're diving something either extremely cheap or old, the chances are that they do not. Same goes for Nitrox, it doesn't make diving any safer. Only the diver makes diving safer by the practices they employ when diving. That being said, Nitrox does extend your NDL bottom time thus allowing you to stay at a certain depth longer than you would for air.

I have noticed that when diving nitrox and not pushing the limits, I feel less fatigued after a dive than I do with air.

Here's another way to look at it, if you want to extend your NDL bottom time limits (within the Maximum Operating Depth for that mix), get nitrox certified. If you are like me and like to increase your chances of observing more marine life, I would recommend it. Just remember you are likely to be just as fatigued diving to the NDL limit of nitrox as you would be diving to the NDL limit of air and all the risk factors remain the same. However, if you exceed the MOD for that mix then you add the risk of Central Nervous System oxygen toxicity.
 
Remember most divers are limited by the amout of as in ther tank. Not how long the dive tables say you can stay down. Divers are usually long out of air (or Nitrox) before they hit that max time.

While this is true at shallow depths, you don't need to be very deep to easily run out of NDL before you are out of gas.

For example an SAC of about 0.5ft^3/min will allow you to max out the PADI RDP by spending 40 minutes at 70 ft using an AL80. Plenty of divers have an SAC that low. To max out your 20min. NDL at 100 ft, you only need an SAC around 0.8, pretty much all but the newbies can manage that.
 
If you are only talking about one dive at a time, then most divers probably are limited by the amount of gas in their tanks, not by nitrogen loading.

However, when considering multiple dives per day on consecutive days, nitrogen can become a limiting factor. In such circumstances, Nitrox can help to mitigate this.

Of course, using Nitrox to gain more bottom time over multiple dives on multiple days can offset any arguable safety benefits one might have gained.

Yes and no on the multiple dives.... Most people I see diving on vacation do two dives in the morning between 40-60 ft with 1-2 hrs surface time between. The gas is almost aways their limiting factor. Then they don't dive till the next day. By then they are only an A diver (no matter whos dive tables you use) so there is only a few minutes of RNT. Not enought to make a difference.....

Now for divers that are doing more dives and nite dives.... I would agree with you.
 
While this is true at shallow depths, you don't need to be very deep to easily run out of NDL before you are out of gas.

For example an SAC of about 0.5ft^3/min will allow you to max out the PADI RDP by spending 40 minutes at 70 ft using an AL80. Plenty of divers have an SAC that low. To max out your 20min. NDL at 100 ft, you only need an SAC around 0.8, pretty much all but the newbies can manage that.


I agree 100%. It just seems everytime I go on vacation the rec divers I see are the ones who are only diving once (maybe twice) a year. Their SAC rate sucks... (No pun intended).... Just seems like everyone is peeling off after only a few minutes bottom time, and when I get back on the boat and ask them they say they sucked their air down..... Oh well more space for me down there then :blinking:
 
Oh yeah I forgot... The gas is more limiting if you are doing multi-level dives (either with tables or computer)... Guessed that would have made a little more sence the first time.. Sorry
 
I agree 100%. It just seems everytime I go on vacation the rec divers I see are the ones who are only diving once (maybe twice) a year. Their SAC rate sucks...

I agree, vacation only divers often have a pretty high SAC, and they'll need to watch their SPG closer than their bottom timer, breathing air or nitrox.

Oh yeah I forgot... The gas is more limiting if you are doing multi-level dives (either with tables or computer)...

If a divers SAC is low enough to break the NDL when deep then multi-level doesn't make much difference. A common profile for me is to dive air to 90 feet to within a few minutes of NDL, and then ascend to 50, 40, 30 feet. When I start my final ascent, my computer often indicates a few hours of NDL remaining, so you could say my dive was gas limited. But, I did build up a significant nitrogen load while deep and nitrox could provide some additional safety or time deep on this profile.
 
I think it is the increased N2 gradient as I ascend from depth which suppresses the size and number of bubbles, which in turn reduces my body's immue system reaction and thus suppresses sub-clinical DCS symptoms such as perceived fatigue and muscle soreness.

I think the truth may lay in this direction as well.

I also think it is worth noting that the body reacts to increased O2 levels not by absorbing more into the bloodstream (21% already provides maximum saturation) but by reducing the actual work of breathing. With more O2 available the body responds by reducing the respiration rate thus the body works less hard. It would be interesting to see (to what degree) the reduced respiratory workload results in decreased fatigue.
 
I think the truth may lay in this direction as well.

I also think it is worth noting that the body reacts to increased O2 levels not by absorbing more into the bloodstream (21% already provides maximum saturation) but by reducing the actual work of breathing. With more O2 available the body responds by reducing the respiration rate thus the body works less hard. It would be interesting to see (to what degree) the reduced respiratory workload results in decreased fatigue.

I think you will find that increased O2 does not effect respiration rate.. as that is mostly driven by CO2 levels...and in many people.. the effect is to increase the respiration rate (slightly more available O2 = slightly higher CO2?)... but the reasons are not clearly understood.

On a cellular level, your post may be very true, but have not read any actual testing of this.
 
I think the truth may lay in this direction as well.

I also think it is worth noting that the body reacts to increased O2 levels not by absorbing more into the bloodstream (21% already provides maximum saturation) but by reducing the actual work of breathing. With more O2 available the body responds by reducing the respiration rate thus the body works less hard. It would be interesting to see (to what degree) the reduced respiratory workload results in decreased fatigue.

Actually, the complications here are hemoglobin and the fact that O2 is used by the body. In normal respiration, hemoglobin is pretty much (but not totally) saturated with O2. As it travels around the body, the O2 is released to the system and replaced (but not completely) with CO2, the result of the body's use of O2. If the diver is breathing very high PPO2, then the hemoglobin is fully saturated and O2 starts to saturate the rest of the blood, just a N2 does. This does not, however change the degree to which the body uses O2 and thereby creates CO2. That is the demand, as PufferFish said, that drives the respiration rate. (By the way, we are treading dangerously close to a discussion of the oxygen window, which I would love to avoid at this time.)

All the talk about nitrox and fatigue is speculation, for there have been no reputable studies related to it. Every now and then someone writes a post referring to the "studies" that show no benefit for nitrox in terms of fatigue, but I have only seen one such study. That study, IMO, was so seriously flawed in its design that its conclusions are worthless. It compared the reported effects on divers on a very basic two tank dive and found no difference in fatigue. What a shock.

Based solely on what I have felt and what I have seen in my own experience, I believe a study of multiple dives over a longer period of time (as on a liveaboard) would indeed show a difference, but since no such study has been done, we are left with sheer speculation.
 
All the talk about nitrox and fatigue is speculation, for there have been no reputable studies related to it. Every now and then someone writes a post referring to the "studies" that show no benefit for nitrox in terms of fatigue, but I have only seen one such study. That study, IMO, was so seriously flawed in its design that its conclusions are worthless. It compared the reported effects on divers on a very basic two tank dive and found no difference in fatigue. What a shock.

Based solely on what I have felt and what I have seen in my own experience, I believe a study of multiple dives over a longer period of time (as on a liveaboard) would indeed show a difference, but since no such study has been done, we are left with sheer speculation.

I do agree with you that there have been no solid findings however even a placebo can have positive effects. My thought process is that as long as the Nitrox is not doing you any harm, and you are not trying to sell it based on said speculation, then it is great if a person BELIEVES that they feel less tired after a Nitrox dives.

This is a purely non-medical or scietific opinion, but every once in a while a placebo can be a good thing.
 
https://www.shearwater.com/products/perdix-ai/

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