Is nitrox worth it for deeper rec dives?

[Compressor]

Yes; thank you Mike.
Locally, LDS wants oxygen cleaning every "few years" for banked nitrox too. So as @rhwestfall said, "insane shop policies out there".

 

[uncfnp]

Pushing into the contingency band? 100+ is already safety stop (which I'd do anyway), 110 is 1.39 PPO2, 115 is about 1.43 (PADI 32% table).

I would not hesitate to do that range on 32.

For non-square profiles, where only a portion of the dive is at max depth, I have been know to touch 120 and even 132 briefly. Remember, its not just depth but depth and time.

 

[BRT]

I would not hesitate to do that range on 32.

For non-square profiles, where only a portion of the dive is at max depth, I have been know to touch 120 and even 132 briefly. Remember, its not just depth but depth and time.

I agree. Obviously risk goes up, but risk of DCS goes up without the nitrox.

 

[kafkaland]

I agree. Obviously risk goes up, but risk of DCS goes up without the nitrox.

In the tradeoff between a risk of OxTox vs. DCS, I would generally choose DCS. OxTox at depth means a seizure and very likely drowning. End of game. A minor DCS hit on the other hand is very survivable and often curable.

 

[BRT]

In the tradeoff between a risk of OxTox vs. DCS, I would generally choose DCS. OxTox at depth means a seizure and very likely drowning. End of game. A minor DCS hit on the other hand is very survivable and often curable.

Yep, but the risk for short exposures at 1.6pp is fairly reasonable.

 

[Gareth J]

Yep, but the risk for short exposures at 1.6pp is fairly reasonable.

Remember (I think) all agencies have modified their training to say that 1.6 PO2 is an absolute maximum. Normally restricted for phases of the dive with low stress and no work (decompression).

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.
Since Nitrox became normal in recreational diving during the 90's, we have backed away from the 1.6PO2 for anything other than decompression.

You are correct to state that the risk of CNS is a product of PO2 and exposure time. But we have all learned that it is far more sensible to be cautious with maximum PO2 exposures. Dealing with a fitting diver underwater is significantly more difficult than dealing with a bend on the surface.

With PO2, discretion is the better part than valour!

 

[Alan Browne]

I would not hesitate to do that range on 32.

For non-square profiles, where only a portion of the dive is at max depth, I have been know to touch 120 and even 132 briefly. Remember, its not just depth but depth and time.

I get it. But. I'm new at Nitrox so I'll be going in on the cautious side until my brain-applied-to-technique to brain-enjoying-the-dive ratio falls to below 40%.

 

[211ratsbud]

@Dive Right In Scuba just needs a booster. LOL Few places outside of cave country will get ya up to the 3k mark on O2 fills.

@Doby45 theres 3300psi of o2 in my 40cf now. Mark our shop down as a frequent flyer for a good solid o2 boost.

 

[Alan Browne]

Remember (I think) all agencies have modified their training to say that 1.6 PO2 is an absolute maximum. Normally restricted for phases of the dive with low stress and no work (decompression).

My PADI EA manual[1] puts 1.4 as max plan and >1.4 .. 1.6 as "contingency" without discussing "contingency" very much. They are quite clear that 1.4 is the limit for rec diving. "Consider the contingency limit - the partial pressures between 1.4 and 1.6 ata/bar - a margin for error only."

The manual goes on to state that if you exceed maximum oxygen exposure limits (as determined by your computer) that you should immediately safe ascend, safety stop and then lay off diving for 24 hours.

It's not clear if that "maximum" (from the computer) is based on entering the 1.4 .. 1.6 O2pp band or in that band (or less) for enough time to absorb too much O2. I'd gather it's the later.

[1] 2010 is what the dive shop sold me. I don't know if there is one more up to date.

 

[Manatee Diver]

The manual goes on to state that if you exceed maximum oxygen exposure limits (as determined by your computer) that you should immediately safe ascend, safety stop and then lay off diving for 24 hours.

It's not clear if that "maximum" (from the computer) is based on entering the 1.4 .. 1.6 O2pp band or in that band (or less) for enough time to absorb too much O2. I'd gather it's the later.

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.

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.