Reasons NOT to use Enriched Air?

[tschmitt]

.... In any regard, I stand by my comment that it is extra important that nitrox divers make sure their tank is full.

I don't remember being taught this in the PADI EANx class. I thought checking/confirming the blend (ie. EANx36) with an analyzer was required, but don't recall ensuring the tank is full or anything. Can someone explain?

Tim

 

[nereas]

Since when is diving to 130ft on EAN32 or EAN40 acceptable? Since when does basic Nitrox cert only allow EAN32 or EAN40? Seems we could both do with a refresher.

Diving to 130 fsw on EAN 32 is no sweat. This would give you a ppO2 of 1.6 ATAs for which the safe oxygen exposure time is 45 minutes. At that depth, your NDL limit is going to be a whole lot less than 45 mins.

Diving with EAN 36 should be limited to 95 fsw, as I said originally, and which you apparently misunderstood.

Diving with EAN 40 makes no sense at all, and you are the only person talking about doing it.

Novice divers are recommened to limit their ppO2 exposure to 1.4 ATAs, and if you are a novice, that is what you should also do.

It normally requires a tech-deco course to fully explain oxygen exposure time limits.

 

[Anti-Hero]

A working dive at a PP02 of 1.6 is risky in many peoples opinion. Typically a PP02 of 1.4 is the accepted working limit, with 1.6 reserved for resting deco.

 

[Rhone Man]

Diving to 130 fsw on EAN 32 is no sweat. This would give you a ppO2 of 1.6 ATAs for which the safe oxygen exposure time is 45 minutes.

I have never done a tech deco course in my life, but I had always understood 1.6 ATA to be the upper limit on pp02 exposure, and it was generally recommended to stick below 1.4 ATA? If that is right then 130 fsw on EAN 32 for 45 mins might be cutting it a little close, particulary given that you are presumably also going to be breathing oxygen at increased partial pressure during deco?

But I am not a tech or deco diver, so maybe I have at all wrong.

 

[nereas]

I have never done a tech deco course in my life, but I had always understood 1.6 ATA to be the upper limit on pp02 exposure, and it was generally recommended to stick below 1.4 ATA? If that is right then 130 fsw on EAN 32 for 45 mins might be cutting it a little close, particulary given that you are presumably also going to be breathing oxygen at increased partial pressure during deco?

But I am not a tech or deco diver, so maybe I have at all wrong.

We normally teach beginners about 1.4 ATAs ppO2 for NDL diving because then there is virtually no way anything can go wrong.

If that works for you, no worries then (as Capt Jack Sparrow said in Pirates of the Carib).

For tech-deco diving, the oxygen exposure limit is an overall factor for the entire dive, and in that case, you would normally be limiting your ppO2 to 1.2 ATAs during the bottom phase, due to the decompression at 20 ft on 100% O2. And you would normally need V-Planner software to determine the overall limit, and it is common to create a margin of error with 80% of the CNS Ox Tox total. But that is a different topic.

 

[Anti-Hero]

We normally teach beginners about 1.4 ATAs ppO2 for NDL diving because then there is virtually no way anything can go wrong.

Sorry dude, but that is blatantly wrong. It is well documented that different physiology responds differently to elevated PP02. It even differs day-to-day on the same individual. There have been numerous cases of people toxing at <=1.4 PO2.

 

[nereas]

Sorry dude, but that is blatantly wrong. It is well documented that different physiology responds differently to elevated PP02. It even differs day-to-day on the same individual. There have been numerous cases of people toxing at <=1.4 PO2.

Urban legends aside, these kind of "low toxing" divers should NOT be scuba diving, then.

 

[Anti-Hero]

Urban legends aside, these kind of "low toxing" divers should NOT be scuba diving, then.

I'm not talking about the mythical 20ft tox. I'm talking about diving elevated P02's within excepted parameters.

 

[String]

I don't remember being taught this in the PADI EANx class. I thought checking/confirming the blend (ie. EANx36) with an analyzer was required, but don't recall ensuring the tank is full or anything. Can someone explain?

Tim

If the station uses partial pressure blending (the most common) they start by putting in a certain amount of O2 then top up with air.
Reason to check its full is to make sure they actually remembered to put the air in (or you're breathing 100% o2).

Analyser will do the trick anyway as it'll tell you the exact % mix.

 

[scubadobadoo]

Would you please supply the source of this information?
.

My sources are DAN and PADI.

This from the techdiver web page sums up my point best..."DAN (Divers Alert Network) has statistics of DCS cases in the USA, which is based on DEMA/NUADC and PADI New Diver Benchmark reports. According to them, the probability to get DCS by air diving is about 0.004% (1 to 25000). Based on this number, and on the PADI Undersea Journal 3/97 magazine, the probability to get DCS by air diving even once during 500 dives is 1.98% (1 to 50). The risk is 1.49% in nitrox diving in same amount of dives. So... so far the difference is marginal, even though nitrox seems to be a bit safer. But an accident doesn't have to be DCS only, and when diving with nitrox there are several other concerns too that air diving doesn't have. Gas blending, analyzing errors, oxygen clean equipments, CNS clock etc. may also be a source of accident. In this point I have to say that nitrox diving is not dangerous when done right, but these points have to be counted when people talk about safety. So nitrox diving is safe, but not safer than air, generally speaking."


I realize that these numbers are far from perfect as are the agencies they come from but at the moment they are the best numbers we have for recreational diving accidents.

In the end, slowing down, getting more training, doing safety stops, slower ascents, better hydration, less consumption of alcohol/drugs, working out etc...will all likely lead to fewer DCS cases. Adding nitrox to the average "air only vacation diver" who fails to do these things isn't likely to make them any safer.