Why dive Deep Air?

[adm3745]

We are running out of helium???

Yup. At the rate we're going, domestic supplies could be depleted in 10 years. Trimix will be unaffordable before that.

 

[Herk_Man]

I quick little story of diving air 30 years ago. Keep in mind I do not condone diving deep on air if there are other options, but also remember deep is a relative term.

I once worked as a dive guide in Hawaii in 1980 - 1989; there were not a lot of rules or knowledge for that matter then
early on we simply used a Hawaiian backpack to hold our tank, this was a metal clamp device that fit over your shoulder, no BCD, we did not have an octopus or many of the other things like computers etc. we memorized the dive tables because we did not plan in advance how deep we would limit ourselves to....60/60, 70/50, 80/40.... Etc.
We dove Molokini every day when there were only two other dive boats going there, and we dove the back side as often as possible which is a shear wall which goes down to 360 feet.
Being young and enjoying having a bit of a buzz on we would do a dive just to get narced. beings that we were doing a couple 100 foot plus dives every day with tourist, then afternoon dives and then maybe a course, then after work or after a night out at the Sheraton disco a 2am dive for lobster. Needless to say we were doing a lot of diving daily and our tolerance was building.
so back to chasing the narc as we called it, we were going deeper and deeper to get good and narced, we would laugh at the other guy who was worse off than us, there were a lot of antics, once we had a girlfriend at around two hunderds who had really long hair and an octopus landed on her head and started attacking her head, we were totally narced out and trippin on this it was like some kind of fun drug that there was no hang over or anything as soon as you surfaced.
Well the deepest we ever went was 240, and it was not to say we went that deep it was because that’s what it took to get us euphoric. Once we where cruising with this giant manta ray at somewhere around 200 - 220 it was like flying in outer space on an alien space ship.

Anyways I only pass this on as a story of diving deep, not smart, we were young, and looking for fun...narcosis is probably what kept our little group of divers from ever doing drugs or drinking to the point of toxicity....

I always used a mantra "Bubbles mean up, bubbles mean up, bubbles mean up" I would repeat this over and over in my head, and on more than one occasion I wasn’t sure what it meant or why I was saying it, I just followed the bubbles until I understood

This all sounds so crazy now...but it is what it is

Like the license plate on the back of my Jeep says, DOOOD !

 

[Andy077]

Yup. At the rate we're going, domestic supplies could be depleted in 10 years. Trimix will be unaffordable before that.

Helium can't "run out" as long as there are radioactive elements in the crust, but it will be harder and more expensive to collect.

 

[TeriLeonard]

Why would you assume that people diving deep on air are not doing deco dives? Diving much past 160, and the time gets so short that you often end up with some deco, even for a short stay.

Also 218 feet isn't some kinda of terrible toxicity threshold that once crossed a diver is immediately in terrible danger. I worry more about narcosis past 220 than oxygen for a bounce dive.

The 218' thing has to do with exceeding 1.6 ATA of oxygen partial pressure while using air. Enriched air training teaches us that oxygen toxicity could occur above that ATA. However, some agencies use 1.6 ATA as a maximum depth with 1.8 ATA as a contingency depth.

Oxygen toxicity can result in unexpected convulsions, at which point the diver would not be able to control keeping the regulator in his/her mouth, and presumably would drown.

Each body is different and so there is no way to predetermine at what point oxygen toxicity will negatively affect a particular diver, which is why PADI remains conservative for recreational diving at 1.4 ATA maximum limit with 1.6 ATA used as a contingency limit. The maximum operating depth is dependent on the percentage of oxygen in the mix.

For instance:
32% O2 = 110' maximum depth (approx. 1.4 ATA)/130' contingency depth (approx. 1.6 ATA)

36% O2 = 90' maximum depth(approx. 1.4 ATA)/110' contingency depth (approx. 1.6 ATA)

 

[boulderjohn]

Yup. At the rate we're going, domestic supplies could be depleted in 10 years. Trimix will be unaffordable before that.

We'll just have to perfect cold fusion.

 

[Blackwood]

Each body is different and so there is no way to predetermine at what point oxygen toxicity will negatively affect a particular diver, which is why PADI remains conservative for recreational diving at 1.4 ATA maximum limit with 1.6 ATA used as a contingency limit.

Isn't that about average (i.e. not conservative) among agency recommendations?

How many teach 1.6ATM any longer? Many teach 1.2 or 1.0.

 

[DCBC]

Isn't that about average (i.e. not conservative) among agency recommendations? How many teach 1.6ATM any longer? Many teach 1.2 or 1.0.

Regardless of what is being taught for recreational divers, air does not present an OxTox hazard for any Navy or Commercial operational diving activity to 250'. If it does, I've never heard of even one diver running into OxTox problems above this depth on air.

I can understand why recreational divers are warned of this hazard, as they are not subjected to the same physical scrutiny as professional divers; which usually includes extensive testing in a dry chamber environment. It is reasonable to take the position that whatever the recreational rates are, that divers dive within these. It does not however indicate that these "rules" should extend to others who have been medically cleared to surpass these limits.

As I have mentioned, when you surpass the recreational diving limit of 130', new rules apply. There is a maximum limit, but it's greater than those mentioned by the recreational agencies. This comes down to getting the proper training before you go past the recommendations.

 

[Blackwood]

Regardless of what is being taught for recreational divers, air does not present an OxTox hazard for any Navy or Commercial operational diving activity to 250'. If it does, I've never heard of even one diver running into OxTox problems above this depth on air.

Yah, that wasn't my point. Just questioning the wording.

 

[TeriLeonard]

Isn't that about average (i.e. not conservative) among agency recommendations?

How many teach 1.6ATM any longer? Many teach 1.2 or 1.0.

Honestly, I am not sure, but since I started working in the dive shop over ten years ago, I have had a number of divers from some of the more tech-oriented agencies, commercial, or the
military share that information with me.

I am unaware of who teaches 1.2 or 1.0. Wow, that's really conservative. Does anyone know who does that? I am curious why. My conservative Suunto computer won't go below 1.2 in nitrox mode.

 

[Rhone Man]

I am unaware of who teaches 1.2 or 1.0. Wow, that's really conservative. Does anyone know who does that? I am curious why. My conservative Suunto computer won't go below 1.2 in nitrox mode.

My understanding was that those advocating lower ppO2s are those involved in really long dives. If you are planning extensive deco, I can see the benefit of keeping your OTUs down. But for conventional recreational use, 1.4 still seems a fairly sensible level.