Nitrox!

[Blackwood]

Here was a brief comment about repetetive dives....

ah, missed it.

 

[Blackwood]

On the other hand, if you dive the same profile as you would on air while using Nitrox, and if you stay well within the MOD of the mixture, how could reduced nitrogen loading NOT be safer?

I've tried. Here's the most recent I could find (from last February):

Given a constant profile:
IF nitrox extends NDL, and
IF diving within NDL provides a safety margin over diving to the limit, and
IF the further one stays from the limit the greater the safety margin is,
THEN nitrox provides a safety margin over air.

No empirical proof is necessary, it's true by definition (assuming the IF statements are true).

 

[udtfire]

coop hit it on the head on thing i try to practice and tell all divers is that slower the better i dive half stops its a great practice for the new diver and a habbit you can live with the way it works for new divers is rise to half your deepest (pause 1 min )depth then half again (pause 1 min)untill you
reach you safety stop then do a full 3-5 min and on the last 15 feet asscent one ft at a time dont race that last 15 feet and this should help develope your bouyance control just my openion use it if you want but always dive safe and thats a yes to nitrox

 

[AndyNZ]

On the other hand, if you dive the same profile as you would on air while using Nitrox, and if you stay well within the MOD of the mixture, how could reduced nitrogen loading NOT be safer?

For an arguable few, on the fringe of a population of divers (with more than one contributing factor from age, obesity, smoking, dehydration etc), then there might be some quantifiable increase in safety.

It's more that the air limits are "so safe" anyway, that the relative increase in safety is so small that it's not even worth thinking about. Claiming nitrox is "significantly safer" doesn't really hold much water. 10% of nothing is nothing.

The impact of a fast ascent is much more quantifiable - even if you're on nitrox, despite the lowered amount of nitrogen then if you make a bolt to the surface then there is a chance of getting a DCI hit.

 

[udtfire]

sorry for the spelling i was rushed

 

[wve]

For an arguable few, on the fringe of a population of divers (with more than one contributing factor from age, obesity, smoking, dehydration etc), then there might be some quantifiable increase in safety.

It's more that the air limits are "so safe" anyway, that the relative increase in safety is so small that it's not even worth thinking about. Claiming nitrox is "significantly safer" doesn't really hold much water. 10% of nothing is nothing.

The impact of a fast ascent is much more quantifiable - even if you're on nitrox, despite the lowered amount of nitrogen then if you make a bolt to the surface then there is a chance of getting a DCI hit.

No disagreement there.

To restate my thoughts on the original question and subsequent replies:

1. It seems illogical to claim that increased nitrogen loading raises the risk for DCS, then also try to claim that decreased nitrogen loading does not lower the risk.

2. Here most people are really offering opinions about the quantity of raised or lowered risk and whether it is worth the trouble, expense, added risk of oxygen toxicity, etc.

3. Comparing air to Nitrox can be like comparing apples to oranges. Depending upon the purpose and expected conditions of the dive(s), one gas could easily be "safer" or "better-suited" than another.

4. If a person is serious about diving, it makes sense to learn all one can about the different gas options in order to pick the mix that will be most ideal for the mission.

5. Appealing to "studies" must be done with care, especially when the studies address infrequent events. The validity of the results depends heavily upon study design and methodology.

 

[boulderjohn]

I
On the other hand, if you dive the same profile as you would on air while using Nitrox, and if you stay well within the MOD of the mixture, how could reduced nitrogen loading NOT be safer?

Yes, indeed, if you are diving the same profile on air as on nitrox, the nitrox will be safer.

However, in terms of the likelihood of getting DCS, both options round off to 0%, so in reality you are not getting much improvement in safety. It is safer, but not to the degree that you want to make any kind of big deal about it, because the risk is so small to begin with.

On the other hand, it does definitely increase bottom times, if you have the breathing skills to take adavantage of it, and if you are working with a diver operator who will allow it. That's why I use it on pretty much every dive I can. I just finished mixing a whole set of tanks of 40% for this weekend, in fact.

 

[cooperscuba]

If reducing nitrogen loading for a given dive does not make it safer - why bother with dive tables or dive planning with regard to nitrogen loading, at all?

RDPs are used to plan no-stop or non-decompression dives (i.e. you can make a direct ascent to the surface at any point with minimal risk of DCS). Safety stops are only mandatory if a diver comes within three pressure groups of an NDL (i.e. they`ve failed to plan or make a dive conservatively within limits) or they dive to 30 meters or deeper (this is based on studies carried out by Andy Pilmanis in 1975). You calculate nitrogen loading with tables to ensure that you don`t plan a dive that exceeds NDLs (i.e. a decompression dive). The level of nitrogen (assuming you plan conservatively within limits) has no effect on DCS - DCS was, is, and always shall be about ascent rates.

How is a low level of nitrogen safer than a higher level if you plan a dive conservatively within limits and maintain a safe ascent rate?

 

[Steve50]

RDPs are used to plan no-stop or non-decompression dives (i.e. you can make a direct ascent to the surface at any point with minimal risk of DCS). Safety stops are only mandatory if a diver comes within three pressure groups of an NDL (i.e. they`ve failed to plan or make a dive conservatively within limits) or they dive to 30 meters or deeper (this is based on studies carried out by Andy Pilmanis in 1975). You calculate nitrogen loading with tables to ensure that you don`t plan a dive that exceeds NDLs (i.e. a decompression dive). The level of nitrogen (assuming you plan conservatively within limits) has no effect on DCS - DCS was, is, and always shall be about ascent rates.

How is a low level of nitrogen safer than a higher level if you plan a dive conservatively within limits and maintain a safe ascent rate?

Simple - The greater the amount of nitrogen absorbed in the tissues, the greater the potential for bubbling.

 

[boulderjohn]

If reducing nitrogen loading for a given dive does not make it safer - why bother with dive tables or dive planning with regard to nitrogen loading, at all?

I know I am repeating myself, but I want to make this clear. Diving within the limits of the tables is already extremely safe. The probability of getting DCS after diving within those limits rounds off to zero. Diving within those limits while on nitrox DOES make it safer, but because diving on air is already so very, very safe, the difference is not statistically significant.