Is nitrox worth it for deeper rec dives?

[Storker]

My original training said take 0.1 PO2 for any negative e.g.; stress, cold, work, fatigue, etc, form the 1.6 limit.
When Nitrox was introduced into the BSAC training, the maximum PO2 to be used was 1.4, (1.6 for decompression - ADP). This was an adjustment from the 1.6 (standard limit) because of UK environmental factors; cold water, stress (low visibility), work (tidal waters). Also, it had become standard in Trimix diving to use a PO2 much lower than 1.6 for the bottom phase of the dive.
Interestingly, I would suggest that was a good decision if you look at subsequent norms, like a maximum PO2 of 1.3 on rebreathers.

I've more or less standardized on EAN32(-ish) as breathing gas when I dive locally since it's included in the membership fee for my club, as long as you're certified and have received training in operating the mixer. At 30m (my personal depth limit), that's 1.3 bar pPO2.

But then I'm a middle-aged average couch potato who hardly ever sees water temps exceeding 10-15 degrees (C) and sometimes down to 4-5 degrees, so maybe it's a smart decision...

 

[MichaelMc]

Oxygen exposure limits are a lot like nitrogen exposure for DCS, except that the consequences of violating the limit can be fatal underwater, it is a factor of time and partial pressure. At 1.4 that is 150 minutes per a dive and 180 minutes per day, and at 1.6 it is 45 minutes per a dive and 150 minutes per a day (per the NOAA Diving Manual 5th edition). They are calculated out as percentages by dive computers and people that need to do more extensive dive planning.

Manatee Diver, Just to be clear, the time limits you are quoting are for pulmonary oxygen toxicity, which causes lung issues, where we have somewhat understood factors of partial pressure and time.

The issue generally of concern as you approach 1.4/1.6 is central nervous system toxicity, which causes convulsions, where all the factors are less understood, so people draw a line at partial pressure. But as most lines, it is fussy and time and others seem factors, but no precise numbers are know. But the 45 minutes at 1.6 is about pulmonary toxicity, CNS toxicity may cause convulsions way before that depending on you, what you're doing, how well your day is going, ...

Edit: Low N2 makes a wider NDL buffer more convenient. Convulsions are really bad. I work at low N2 while staying a decent margin from convulsions.

 

[tarponchik]

Another consideration is that most of the people I buddy with do NOT dive nitrox on a regular basis. What's the point in paying for O2 cleaning and the additional cost of nitrox if your buddy has to ascend earlier than you do?

Exactly. At any depth, if EAN can't deliver longer bottom times for you, avoid it.

 

[Storker]

if EAN can't deliver longer bottom times for you, avoid it.

So... are you saying that you actively try to avoid a significantly lower N2 loading?

 

[PfcAJ]

Manatee Diver, Just to be clear, the time limits you are quoting are for pulmonary oxygen toxicity, which causes lung issues, where we have somewhat understood factors of partial pressure and time.

The issue generally of concern as you approach 1.4/1.6 is central nervous system toxicity, which causes convulsions, where all the factors are less understood, so people draw a line at partial pressure. But as most lines, it is fussy and time and others seem factors, but no precise numbers are know. But the 45 minutes at 1.6 is about pulmonary toxicity, CNS toxicity may cause convulsions way before that depending on you, what you're doing, how well your day is going, ...

Edit: Low N2 makes a wider NDL buffer more convenient. Convulsions are really bad. I work at low N2 while staying a decent margin from convulsions.

You are incorrect.

The figures you’re talking about here ARE CNS guidelines.

Shearwater and the CNS Oxygen Clock - Shearwater Research

Oxygen Toxicity - Signs and Symptoms | Dive Rite

 

[tursiops]

Exactly. At any depth, if EAN can't deliver longer bottom times for you, avoid it.

That is an opinion. Others may think otherwise.

 

[tarponchik]

That is an opinion. Others may think otherwise.

Sure. But this is what PO asked for: opinions.

 

[tarponchik]

So... are you saying that you actively try to avoid a significantly lower N2 loading?

As long as I do not get DCS, I do not care about N2 loading. And if Joe and Jane are back on the boat with me after we had the same bottom time, why would I care who got more N2? My body doesn't care either. But I do believe that excessive O2 is bad for you because, unlike N2, oxygen is not chemically inert and it damages DNA and other vital molecules in our cells. Whether you buy this argument or not I do not care. We've been through endless discussions of the subject here on SB and I am well aware that my opinion is an irritant to many folks here, especially, for the "I-just-feel-good-breathing-NITROX" and "I-am-always-right-because-I-am-an-MD" types, but this is my opinion.

 

[Storker]

this is what PO asked for: opinions

If it were just an opinion, it might have been more productive to phrase it as just that: an opinion.

As long as I do not get DCS, I do not care about N2 loading.

That's your choice. I happen to disagree.

this is my opinion

You know what they say about opinions? They're like arseholes: everyone has one.

 

[Alan Browne]

Also the PADI EAN manual though it is probably good enough for understanding the dangers for recreational contexts, leaves a lot of information out of the manual. I wouldn't reference it for anything but seeing the official PADI stance on EAN diving.

I do find the PADI EAD manual to be somewhat sparse as in "this is what you need to know to pass our exam and not much more."

That said, my ass, my conservatism.