To Nitrox or not to Nitrox: that is the question

[Carribeandiver]

Just plain curiosity... do you do a lot of deco dives ? A lot of dives in the 30m/100ft range ? A lot of dives of 60 to 120mins ? A lot of dives in water temperatures in the below 10C (below 50F) range ? Do you do a lot of dives with 7mm exposure suits ? Do you do a lot of dives where you have to 'struggle' against current, and in low viz ?

As my name implies, 90% of my dives are in warm water. My normal exposure suit is a .5 mil although in winter I wear a 1.0 mm suit. I have been on live aboards with up to 4 dives in a day and at least 2 of those are in the 60 to 100 foot depth range. My bottom time depends on my depth but I have done dives of 50 minutes or longer but those are all in depths of 50 feet or less.
No, I do not do any deco dives. The deepest I have been is around 110 feet and I have no desire to go any deeper. And, I have been in stiff currents a few times and I cannot say I am wild about that either. Drift dives are terrific but swimming against a 2 or 3 knot current is a nightmare. I have one particular dive in the Bahamas where I swam against a very stiff current and my air consumption was close to 2 cfm whereas on normal dives my air consumption is around .60 cfm.

 

[ianr33]

I agree with Don and DAN. Those are the only two real reasons of major concern. The "chance" of getting DCS is ALMOST ALWAYS dictated by the diver's diving habits and not the gas one chooses. In fact, it has not been proven statistically yet that Nitrox will lead to fewer DCS hits but in the end, we all know that less nitrogen is typically better. The class is a good one even just for the material covered.

I have never understood this argument that nitrox does not decrease the risk of DCS.

Lets go dive together.We are going to do 100 feet for 25 minutes.Ascend at 30 feet/min and then do a 3 minute safety stop. I will dive 32%,you can dive air.

No matter what DAN or the statistics may say,you are much more likely to get bent.

 

[HowardE]

Nitrox only reduces DCS when you compare a similar profile to a leaner mix (or air). There is an apparent reduction of risk, because of increased NDL times. As a gas by itself, nitrox has no medical benefit to reduce DCS.

 

[scubadobadoo]

I have never understood this argument that nitrox does not decrease the risk of DCS.

Lets go dive together.We are going to do 100 feet for 25 minutes.Ascend at 30 feet/min and then do a 3 minute safety stop. I will dive 32%,you can dive air.

No matter what DAN or the statistics may say,you are much more likely to get bent.

Let me try to clarify as you are partially correct but not specifically in the context of my argument. You misssed the part where I stated, "The "chance" of getting DCS is ALMOST ALWAYS dictated by the diver's diving habits and not the gas one chooses." Diving the above profile you suggest (on air) would fall into that above category of bad diving habits and may I say even STUPID diving habits. Check your tables.

I think you are confusing nitrox benefits with statistical data. Clearly, nitrox has benefits. More dive time at depth being typically one of them as your above dive profile shows. That said, there is NO statistical data to suggest or prove that using nitrox has lead to fewer cases of DCS. I'll go with DAN on this one. They have a little bit more credibility than you. Nothing personal. What I state is fact and not an opinion, for the moment, until more data is available.

In the end, when I want more dive time I will use nitrox. I don't choose nitrox to make me a safer diver, I use better judgement to do that.

Diving to 100 feet for 25 minutes on air gives me a greater DCS risk because I am a stupid diver. That has nothing to do with nitrox use.

Nitrox only reduces DCS when you compare a similar profile to a leaner mix (or air).

Even then, there is no statistical proof that diving nitrox on air tables decreases DCS hits at all, let alone minimally. That said, it is obvious that it does decrease nitrogen exposure and that's obviously a good thing. I still agree with DAN that diving within limits, ascending slowly, and doing saftey stops helps more than the gas a diver is breathing.

I know, I know, I am splitting hairs here.

 

[ianr33]

O.K. Lets put this another way

Nitrox will let you do dives within NDL limits that you could not do on air.(e.g.100 feet for 25 minutes)

If you are in the habit of doing multiple,aggressive profiles right up to the NDL (riding your computer) then doing THE SAME DIVES on nitrox will reduce your risk of DCS

Diving up to an NDL on air probably has the same (small but not zero) risk as diving up to an NDL on nitrox

Doing mild profiles (e.g. 50 feet for 20 minutes) the risk of DCS is essentially zero anyway,so nitrox will have no benefit.

I am amazed that people can spend so much time arguing about this stuff.

 

[scubadobadoo]

If you are in the habit of doing multiple,aggressive profiles right up to the NDL (riding your computer) then doing THE SAME DIVES on nitrox will reduce your risk of DCS

Maybe. Theoretically, yes. Statistically, no.

 

[Charlie99]

Seriously, Nitrox has its place and the Flower Gardens is one of those places where it does help if you want to take advantage of what it offers.

What sort of profiles do you dive at the Flower Gardens?

SE Florida is another place where nitrox helps a lot. Boat dives on the 3rd reef are usually 60-90' to the bottom, and the reef has relatively little relief, so most of the dive will be near maximum depth. I've found those close-to-square-profile dives is where nitrox really helps.

In Maui I'll do dives that are both deeper and longer, but they are usually multilevel wall dives and have significant time spent shallow towards the end. For those dives, air isn't a big limitation because of the offgassing from the time wandering around at 40' and shallower. The few dives with NDL limits are a problem are some relatively flat bottomed dives, either a 65' artificial wreck, or so other near shore sites that are 80-110' bottom with only 10' of reef.

 

[ianr33]

Does anybody have a link to this DAN article we are arguing over (nitrox does not,statistically,reduce DCS)

 

[String]

If you are in the habit of doing multiple,aggressive profiles right up to the NDL (riding your computer) then doing THE SAME DIVES on nitrox will reduce your risk of DCS

Got any data to back this claim up? Its totally the opposite of what published research showed.

 

[in_cavediver]

Maybe. Theoretically, yes. Statistically, no.

I would say the benefits are real but very small for any dive profile and they increase incrementally with repetive dives.

Looking at this with a tissue model, diving the exact same profiles with air and nitrox, your body will ongas more inert gas with air than nitrox. Since you ongas more with air, you will have more to offgas at the surface. Since it's identical profiles, after dive 1, the air diver is starting each dive with a larger residual inert gas load. At the end of the day, the air dive WILL have a larger inert gas load than the nitrox diver.

Will it lead to DCS, maybe so, maybe not. The air diver is a lot closer to that magical (and moving) DCS threshold though.