Don't breathe tanks to zero?

[The Chairman]

As an old fart, I dive NitrOx whenever possible and/or practicable. I might do 4 or 5 dives in a day and sometimes for a few days in a row, depending on weather, etc. One of my favorite instructors here in the Keys has semi-retired from teaching due to the abuse N2 has been wreaking on his body. He doesn't see the need for NitrOx either. Go figure.

 

[Abdullah]

The human body does have a tolerance to certain levels of nitrogen loading with apparently no adverse effects. This is what dive tables and computers try to reflect when they tell you that your NDL is in the order of hundreds of minutes for certain shallow depths.

When you reduce N2 loading by replacing it with O2 loading you are not necessarily getting a freebie in the long run. O2 loading increases free radicals in your body and it is an oxidizing agent. Have you heard in the media of products that claim to be powerful antioxidants that help slow down aging? Well, O2 is the opposite. It is a powerful oxidant.

Oxygen is a strong oxidant, but aren't the troublesome oxidants in the body various bioactive complex molecules? I don't think the science supports this argument.

 

[Slamfire]

Oxygen is a strong oxidant, but aren't the troublesome oxidants in the body various bioactive complex molecules? I don't think the science supports this argument.

When you supplant N2 loading with O2 loading you are absorbing more oxygen than is required for breathing. You do get excess O2 dissolved into your tissues, just as you do get dissolved N2. From the DCS point of view O2 loading is not as troublesome as N2 because O2 gets metabolized and will not cause the DCS damage that similar N2 loading might. Metabolized means that it will interact with the various bioactive complex molecules.

As an old fart, I dive NitrOx whenever possible and/or practicable. I might do 4 or 5 dives in a day and sometimes for a few days in a row, depending on weather, etc. One of my favorite instructors here in the Keys has semi-retired from teaching due to the abuse N2 has been wreaking on his body. He doesn't see the need for NitrOx either. Go figure.

Can you supply any information about the long term effects of frequent moderate N2 loading? For example, what are the long term consequences of loading your body to a gradient factor of 70 x times a week for 15 years? I would be very interested in learning this. Right now, because I am in ignorance of any long term studies of repeated exposures to moderate N2 loading (eg GF 70), your statement sounds as well founded as claiming that cooties caused these unspecified damages wrecking his body.

Are you referring to brain and nervous system lesions that do not initially and by themselves cause noticeable DCS symptoms but that get a joint cumulative toll on your nervous system? Bone necrosis maybe? Has he had MRI's or other medical diagnostics that conclusively point to diving air as the culprit?

---------- Post added July 6th, 2013 at 09:51 AM ----------

Before this thing starts flaming up in my face, I am NOT saying that Nitrox is a bad thing and diving Air is a good thing. Very few things in life are clear cut black and white. I use nitrox extensively. There are risks and benefits for either. I'm just pointing out to some of the potential risks in long term nitrox usage. The fact is that US people have a life expectancy of 78.7 years (81 years if you're Canadian ). I enjoy diving. I know there are risks. I chose to do it anyway given that I only have a little more than 40 years left ...if Im lucky.

 

[Tortuga68]

Yes I took the class. Not sure what it is blended with. Assume a mix with much lower o2 levels than what you have at the end since it is starting 100% o2. When I picked up the tanks I watched them hook them to the gauge and test them and saw the percent 02. I don't have my own gauge if that is what you mean

Nitrox when blended is done with air (21%) and O2 (100%) to get the desired mix. Not air and nitrogen

I do it all the time. On big dives where my big doubles are not enough for bottom gas by themselves I'll breathe down the stage until it starts getting difficult to breathe out of it (around IP ~130psi). I will also do this for repetitive dives where doubles will not give me decent bottom times for 2 dives

What mixes are you using in your stage and doubles?

 

[Slamfire]

What mixes are you using in your stage and doubles?

They're usually the same or very close. If they are not and I plan on draining a stage, back gas will be compatible (albeit possibly less optimal) with the depth I plan on being when it gets drained. In other words, stage might be slightly richer (eg 22/20) but back gas (eg 18/30) is still safe at the draining depth (eg 150 ft).

Attached you will find a real life example from my log.

View attachment Flash.pdf

 

[Tortuga68]

They're usually the same or very close. If they are not and I plan on draining a stage, back gas will be compatible (albeit possibly less optimal) with the depth I plan on being when it gets drained. In other words, stage might be slightly richer (eg 22/20) but back gas (eg 18/30) is still safe at the draining depth (eg 150 ft).

Attached you will find a real life example from my log.

View attachment 159039

I guess what I'm wondering is what you're using for deco and why you don't (as it seems) breathe a deco mix (from your stage)

Since it appears your backgas and stage are pretty similar, what's your rationale for breathing the stage down?

 

[Slamfire]

I guess what I'm wondering is what you're using for deco and why you don't (as it seems) breathe a deco mix (from your stage)

Since it appears your backgas and stage are pretty similar, what's your rationale for breathing the stage down?

I do breathe deco gas from the other slinged bottles. Bottom gas stages and deco bottles are not mutually exclusive. In the attached example (just click on the link Flash.pdf) I am slinging 3 bottles: 22/20 (was drained), EAN 51%, O2. I was also carrying double LP108's on my back with 19/20. This was a 4 gas deco dive. The point for carrying bottom gas stage is to:

1. Expand the quantity of available bottom gas and/or
2. Have more gas leftover in the backmounted doubles for another deco dive on that same day/trip or any other day

 

[The Chairman]

Can you supply any information about the long term effects of frequent moderate N2 loading?

No, and I don't think it's out there, either way. We talked briefly with our friend two nights ago. All of his "niggling symptoms" sounded like DCS to me. Now, I'm not a medical doctor (important disclaimer there), but I've heard enough people describe their symptoms to be able to delineate between just getting old and what appears to be recurring DCS injuries. There was no doubt in my mind that he was suffering from cumulative DCS injuries. As much as I dive, he dives far more than me. Again, I am a very cautious diver and so far I have yet to experience any DCS personally. It's not a matter of denial as I have any number of ailments induced by arthritis as well as obvious injuries from diving.

 

[chrpai]

So how are these claims any different then some random dive shop employee / professional splurging out some random FUD?

Sorry if it seems like I get "defiant" but I've heard this song too many times over the years. Arguments of authority are frequently heard in this community. People can't admit "I suspect, but we really don't know." They just have to make things sound like facts and your and idiot for disagreeing.

 

[Panama Jones]

At dinner some divers were saying that you if a tank gets breathed down to near zero pressure, bad things can happen TO THE TANK. Something about humidity and rust, refilling the tank and then breathing head down.

What's the story here?

Bill

We got a great lesson in nitrox and other gasses but to answer your question I did a few experiments with two set of regs and mostly empty tanks. Oceanic (new) and Mares (older) reg.

On both, after purging or breathing down, the first stage stopped delivery while the tanks were both positively pressurized. In other words, if I purged it down, turned off the valve, disconnected the regs, and then cracked the valve, I got air from the tank.

Given a good dry fill (no contaminants or humidity in the tank from the original fill), for my setup you could breath it till you could not get any more and still not have a problem unless you left the tank valve open to depressurize to ambient.

Of course always dry the valve and put the valve cap on after your dive. Whether breathing them down while diving is a good idea or not is not important to the question.

BTW this is how biolabs and hospital isolation rooms keep germs and viruses out right? Simple physics again.