Alternating Nitrox and Air dives ok on ProPlus 3?

[tursiops]

But how can nitrogen make you tired (or feel tired)?

I don't know, not my field. Maybe the answer is in studies like this: Potential molecular mechanisms underlying muscle fatigue mediated by reactive oxygen and nitrogen species. - PubMed - NCBI.
Maybe it is related to the sedative properties of Nitrogen (narcosis, various nitrogen-compounds that have direct affect, like nitrous oxide).
Good question for the specialists.

 

[tarponchik]

I never disagreed with you on anything. I know and understand that nitrox is used in order to increase bottom time. I simply said that you increase the "safety factor". You do not know by how much , so why would you want to start an argument?

Having said that, I have an issue with this statement of yours, giving the impression that what I wrote was wrong.:

"The "official" nitrox instructor response is that diving nitrox with an air profile does not make you safer. Actually, it does make you safer, but only so slightly that it is not statistically significant. Although it is impossible to estimate precisely the risk of DCS on a NDL dive, it is extremely low--I have seen the number 0.002% used with some frequency. If you improve your safety by 50%, then you have improved it to 0.001%. Congratulations!"

The deco procedures have been established on statistical occurences of DCS hits. I am not an instructor at your level, but the scientist that I am has a problem with the above statement. You just cannot say that it does not make you safer, then it does make you safer, then there is no statistical difference.

20 vs 10 cases per million dives gives me p=0.034 and this is statistically significant; however, these are extremely small numbers that can hardly justify any action. You can also dive on Nitrox but set your comp on air. This will add you another 50% safety factor, down to 5 cases per million

Also, unlike nitrogen, oxygen is a reactive chemical and your body has a defense mechanism against it for a good reason. The long term effects of oxidative stress are not well known. The guidelines we follow on the pulmonary toxicity of O2 is based on short-term effects. See, for example, this.

 

[tarponchik]

I don't know, not my field. Maybe the answer is in studies like this: Potential molecular mechanisms underlying muscle fatigue mediated by reactive oxygen and nitrogen species. - PubMed - NCBI.
Maybe it is related to the sedative properties of Nitrogen (narcosis, various nitrogen-compounds that have direct affect, like nitrous oxide).
Good question for the specialists.

Thanks! I have 2 comments on this article. 1st, they talk about "intensive contracting activity", and this is some kind of heavy lifting, definitely not scuba diving. 2nd, reactive nitrogen species (or RNS) is not nitrogen but various nitrogen oxides, NO, nitrosamines, peroxynitrite, stuff like that. This stuff can inflict some chemical damage on your body systems.

 

[boulderjohn]

But PADI can't now publish that 30 is the safe ascent rate....because what about the liability from all those years they said 60?

I can't say for certain, but I don't believe that is the concern. The PADI RDP was calculated after scads of very expensive research using 60 FPM as the ascent rate. All the numbers on that table are based on a 60 FPM ascent rate. The research they did said that those numbers are safe with that ascent rate. If they change the ascent rate, the table has no experimental validity.

In the computer OW course, they tell you to use whatever ascent rate is specified by your computer. That makes sense, because the computer's algorithm is based on that specified rate. That is consistent with using 60 DPM for the tables, since that is the rate upon which they were based.

 

[diverdoug1]

I am a hyperbaric physician and I treat a number of "undeserved" cases of DCS every year. When I dive I use nitrox to decrease my equivalent air depth and nitrogen tissue loading (as the max. depth of my dive profile will allow). Regardless of the low incidence of "undeserved" DCS, I don't mind paying the chump change it costs to use nitrox if it will significantly decrease my already low chance of DCS. I feel I am worth it. Some other things that I do that make me safer (even though the initial risk is already low) are;
wear a seatbelt
stay out aircraft with inexperienced pilots
wear a helmet when horseback riding
wear a lifejacket while fishing
get TDAP booster every 5 years
Rotate my tires every 5000 miles

I am haunted by a debate I had with TSandM (Lynne) about 4 years ago on Scubaboard Pace of Cave Diving Instructional Progress . I was supporting the position that all divers should get a yearly physical exam, while she was arguing that the overall risk for divers having a medical incident while diving was very low to begin with. I explained to her that if many small and seemingly insignificant risks are decreased, the overall risk reduction can be significant. Her untimely and tragic death while diving has caused me to frequently reflect on this debate we had

 

[Freewillow]

I am a hyperbaric physician and I treat a number of "undeserved" cases of DCS every year. When I dive I use nitrox to decrease my equivalent air depth and nitrogen tissue loading (as the max. depth of my dive profile will allow). Regardless of the low incidence of "undeserved" DCS, I don't mind paying the chump change it costs to use nitrox if it will significantly decrease my already low chance of DCS. I feel I am worth it.

Let me sure I understand you. You mean decreasing an already low risk by diving nitrox with an air table - or computo? Is this correct?

 

[tarponchik]

Yes, some folks do just that. They use air tables or computer settings while diving Nitrox. I also liked the tire rotation after 5,000 miles part.

These are probably the same people who always go 10 miles below the speed limit, treat every "yield" sign as "stop" and put rubber gloves on when toasting bread to reduce the risk of electric shock.

 

[diverdoug1]

Let me sure I understand you. You mean decreasing an already low risk by diving nitrox with an air table - or computo? Is this correct?

No, I attempt to use the optimum gas for the dive I plan on doing. Minimizing my EAD, but keeping my ppo2 below 1.4 atm. I usually use a mix that has a MOD the will give me a ppo2 of 1.2 at my planned max depth so that I have a little extra depth capability for contingencies. I think diving nitrox while your computer is set on air deprives you of the backup computer warning of exceeding your MOD (of course your should always remain cognizant of how your current depth relates to your gas MOD). I really don't see a huge benefit of using air tables or setting your computer to an incorrect setting. If you wish to further increase your safety margin, then just shorten your bottom times.

 

[Dolpheye]

Newish diver who was looking for real information and can't help but comment on how disappointing it was to read this post be so hijacked by argument that absolutely should have occurred elsewhere

Back to original topic...(I own PP3) I'm about to do LAB with free Nitrox and do not understand why you would change gases underwater??? That seems terribly awkward - you are connecting your tank above, why are you not able to set gas then?

 

[Freewillow]

Newish diver who was looking for real information and can't help but comment on how disappointing it was to read this post be so hijacked by argument that absolutely should have occurred elsewhere

Back to original topic...(I own PP3) I'm about to do LAB with free Nitrox and do not understand why you would change gases underwater??? That seems terribly awkward - you are connecting your tank above, why are you not able to set gas then?

The initial question was answered with the first intervention. It was yes. So why would you be dissapointed?

When it comes to YOUR question, I do not understand it. I am prepared to help but explain what LAP means. Thank you.