Equivalent Air Depth question

[Bob DBF]

You narcosis will most likely be worse using nitrox as you extend your bottom time, if you believe O2 to be equally narcotic.

The more time you spend at depth, the more you are likely to experience narcosis.

I read the extending of bottom time as why one is using nitrox, rather than it being a function of the narcosis. I probably would have structured my explanation differently.

The more time you spend at depth, you have more chances to notice you are narked, even though you are narked the entire time.

 

[tursiops]

The more time you spend at depth, you have more chances to notice you are narked, even though you are narked the entire time.

Bingo

 

[Akimbo]

Don't assume everything told to you in your OW class -- no matter which agency -- is 100% true. It may have been true at some point in the past (like telling you to turn your tank valve back off 1/4 turn after opening it) but is no longer valid.

For other readers​

The 1/4 turn back-off technique is still valid with some valve designs from the 1950s. Valves changed but the reasons behind most rules have been dropped from recreational diving classes for economy and customer tolerance.

The US and Royal Navy's maximum PPO2 was 3.0 for combat swimmers when World War II started. It dropped to 2.0 after the Brits actually tested it in wet chambers instead of dry. Lots of theories but there is no definitive reason why being wet makes such a difference, but it proved to be. It was 2.0 until around the 1990s. Physiology has not changed, but risk tolerance has. Same with safety stops.

Most rules exist for convenience, not precision — the lazy man's substitution for knowledge. That is OK until you start to believe that a rule is based on absolute fact that is uninfluenced by any other factors.

Sure you can hold your breath on Scuba. You can also hold your breath on Scuba while ascending. It is a really bad idea from 10M to the surface, but not much problem from 200M to 190. You just can't hold your breath on Scuba while ascending until the gas expands enough to blow your lungs out, which is not a good look for booking advanced dive classes. The whole issue of AGE has been dumbed down to "don't hold your breath", which makes some new divers afraid to swallow their spit.

Gas narcosis is a very murky area with wide human variability, between individuals and day to day. There is a lot going on that we don't understand, but work around reasonably well.

 

[tursiops]

The 1/4 turn back-off technique is still valid with valve some designs from the 1950s. Valves changed but the reasons behind most rules have been dropped from recreational diving classes for economy and customer tolerance.

True, but the point is the valves did change.....so the "rule" was once quite valid, but now it is an anachronism...never the less you hear it in nearly every OW class.

 

[Celt]

I read the extending of bottom time as why one is using nitrox, rather than it being a function of the narcosis. I probably would have structured my explanation differently.

The more time you spend at depth, you have more chances to notice you are narked, even though you are narked the entire time.

Narcosis is dose dependant, the longer your exposed to the depth the greater the chance of suffering narcosis.

 

[Akimbo]

True, but the point is the valves did change.....so the "rule" was once quite valid, but now it is an anachronism...never the less you hear it in nearly every OW class.

Yep, rules never seem to retire. Remember being told that you can't go in the water within an hour of eating?

Does Plucking a Gray Hair Make More Grow? And More Old Wives Tales That Are Fake

These long-believed "facts" don't exactly hold any truth.

www.goodhousekeeping.com

 

[scubadada]

Yep, rules never seem to retire. Remember being told that you can't go in the water within an hour of eating?

Does Plucking a Gray Hair Make More Grow? And More Old Wives Tales That Are Fake

These long-believed "facts" don't exactly hold any truth.

www.goodhousekeeping.com

My parents subscribed to that belief, 1950s-1960s

 

[Akimbo]

Narcosis is dose dependant, the longer your exposed to the depth the greater the chance of suffering narcosis.

Duration can have the opposite effect. Just as deep ventilation can reduce the effect (through CO2 reduction), so can habituation — or perhaps some other unknown bit of physiology.

I have been a tender on treatments to 165'/50M, both inside and outside the chamber. In every case, the performance noticeably improved after 10-30 minutes. Was it NN or just getting past the silly-inducing voice change? It's anyone's guess.

I have also been on air diving jobs in that depth range. Performance increased after a few days, mistakes reduced and job completion times improved. Is that relearning to deal with NN (habituation), a physiology change, or something else. I have seen and experienced it too often for it to be baseless.

 

[Celt]

Duration can have the opposite effect. Just as deep ventilation can reduce the effect (through CO2 reduction), so can habituation — or perhaps some other unknown bit of physiology.

I have been a tender on treatments to 165'/50M, both inside and outside the chamber. In every case, the performance noticeably improved after 10-30 minutes. Was it NN or just getting past the silly-inducing voice change? It's anyone's guess.

I have also been on air diving jobs in that depth range. Performance increased after a few days, mistakes reduced and job completion times improved. Is that relearning to deal with NN (habituation), a physiology change, or something else. I have seen and experienced it too often for it to be baseless.

Different people have different tolerance to narcosis. But I think what you’re describing is becoming somehow acclimatised for want of a better word. This happens when you make repeated deep working dives over a short time increasing the depth gradually. I’ve done that to 70 metres but everyone has a limit and it doesn’t last. After a break of a few weeks your back to square one.

 

[Wibble]

Problem with narcosis is you’re largely unaware of the affects until it’s serious. A lot like watching a youth drinking alcohol, they’re unaware of their behaviour as others around them see it very differently.

Main times I’ve noticed it is doing a fast decent beyond recreational depths on nitrox, 45m+ / 150ft+. A more gentle descent, such as to the top of the wreck and subsequently descending to the bottom goes unnoticed.

The cure is a rebreather and diving with helium all the time.