Question How to dive nitrox for the first time

[NothingClever]

SSI is just plain dumb for granting even a narrow allowance for divers to set a computer differently from the gas one’s breathing.

Unbelievable.

 

[arkstorm]

It's an easy ballpark number to remember. Of course if you are diving far below ppO2 limit and you have the computer to monitor your oxygen exposure in real time, you can probably dive much longer.

View attachment 895795

I think that table creates confusion and misunderstanding regarding the risk of O2 exposure...

You are not generally limited to 180 minutes of diving over 24 hours even when breathing EAN.

The time limit corresponds to how much time you can remain at your MOD, i.e., at PPO2 of 1.4 ata, for the entirety of the dives, only then are you limited to 180 mins of exposure over 24 hours.

For example, if you are diving EAN32, you would have to stay at 111 fsw for >180 minutes within a 24 hour period to reach that limit.

Consider a LOB where you are doing five 60' dives a day on EAN32 but you are nowhere near your MOD. you could easily do five 60-minute dives, 300 minute total, and not get anywhere near your O2 exposure limit.

A much better way of explaining this concept is that a diver is allowed a limit of 300 oxygen toxicity units (OTU) per day. One OTU is equivalent to breathing 1.0 ata of O2 for one minute.

Dive computers do an excellent job of calculating this exposure in real time based on your actual gas loading per your varying depth but you have to tell the computer what gas mix you are breathing...

That is yet another reason not to dive an air profile on nitrox when using a computer.

 

[uncfnp]

A timely discussion…

Info Thread 'Some History of the NOAA Oxygen Limits'

Jan 2, 2025

It is popular on ScubaBoard to denigrate the NOAA Oxygen Exposure Limits, which were originally (from the NOAA Diving Manual 2nd Edition, 1979) given as:

The source of this table is clearly stated as the USNavy Diving Manual (1973).


By the NOAA Diving Manual 3rd Edition (1991) the limits had become:

The source of this info is clearly stated as from Butler and Thalmann (1986) and other data.

The 4th Edition (2001) of the NOAA Diving Manual gives:

The source is cited as:

The U.S. Navy has recently performed research on pure oxygen diving in...​

• tursiops
• Replies: 32
• Forum: Technical Diving

• 
• 
• 

 

[Blackcrusader]

SSI is just plain dumb for granting even a narrow allowance for divers to set a computer differently from the gas one’s breathing.

Unbelievable.

If this was the case why have a nitrox cert in the first place. When I was at Savedra a non certified Nitrox diver asked could he use nitrox on his dives and was told NO. He thought he could just use 21% settings and dive on 32%. When asked what the MOD of 32% was the diver didnt know. When asked what the MOD of 21% was the diver didn't know.

 

[boulderjohn]

It's an easy ballpark number to remember.

Any random number is easy to remember. Being easy to remember does not make it right.

 

[halocline]

Any responsible operator would not mix air and nitrox divers together.

That’s an oversimplification, and the fact is that in the real world, recreational dive boats mix nitrox and air divers without any problems. There’s nothing wrong with that as long as the nitrox divers understand they may not get the full bottom time benefit of their gas. It just depends on the dive profile, the amount of independence divers on the boat have, and what the expectations of the nitrox divers are. Lots of recreational divers use nitrox simply to lower their N2 loading; they’re frequently limited by gas rather than no deco limits anyways.

 

[gamon]

That’s an oversimplification, and the fact is that in the real world, recreational dive boats mix nitrox and air divers without any problems. There’s nothing wrong with that as long as the nitrox divers understand they may not get the full bottom time benefit of their gas. It just depends on the dive profile, the amount of independence divers on the boat have, and what the expectations of the nitrox divers are. Lots of recreational divers use nitrox simply to lower their N2 loading; they’re frequently limited by gas rather than no deco limits anyways.

Well to me at least, having to cut my bottom time short by as much as 30 minutes to accommodate air-only divers is a big problem. Especially if the dive charters that mix groups together will not permit buddies to surface after the group (or solo divers on their own).

Don't know where you get the idea that 'lots of divers use nitrox simply to lower their N2 loading' and why what lots of people do is even relevant because my personal preference to use it to shorten bottom times and/or surface intervals.

 

[halocline]

Well to me at least, having to cut my bottom time short by as much as 30 minutes to accommodate air-only divers is a big problem. Especially if the dive charters that mix groups together will not permit buddies to surface after the group (or solo divers on their own).

Don't know where you get the idea that 'lots of divers use nitrox simply to lower their N2 loading' and why what lots of people do is even relevant because my personal preference to use it to shorten bottom times and/or surface intervals.

What you personally want out of nitrox on a given dive does not dictate what “any responsible operator” would need to do. How difficult is that to understand? This is my problem with responses like yours, which essentially establish rules of conduct for others based on your wishes or opinions. The fact is that using nitrox for a dive that others are doing on air is not unsafe, (as long as MOD limits are followed) it doesn’t violate any industry protocols, and I’ve seen divers do it dozens of times on recreational charters.

 

[gamon]

What you personally want out of nitrox on a given dive does not dictate what “any responsible operator” would need to do. How difficult is that to understand? This is my problem with responses like yours, which essentially establish rules of conduct for others based on your wishes or opinions. The fact is that using nitrox for a dive that others are doing on air is not unsafe, (as long as MOD limits are followed) it doesn’t violate any industry protocols, and I’ve seen divers do it dozens of times on recreational charters.

You're the one who is not understanding. This isn't about the safety of nitrox, it's about limitations imposed on nitrox divers by mixing them with air divers.

There are lots of responsible dive operators with whom I've experienced satsifying and enjoyable dives, who either don't mix nitrox and air divers in one group and/or allow buddy teams or solo divers to surface on their own after the air divers have reached their ndl limits.

 

[NothingClever]

Well to me at least, having to cut my bottom time short by as much as 30 minutes to accommodate air-only divers is a big problem. Especially if the dive charters that mix groups together will not permit buddies to surface after the group (or solo divers on their own).

Name the charter operation and body of water that’s cutting your EANx dive short and making you surface with the air divers.