100% 02 during your SI?

[Ulfhedinn]

Does anyone breath 5mins or so of 100% 02 between dives? Seems like it would assist in lowering your PG. Is my thinking off>?

[Deep South Divers]

No, your thinking is not off. Given a "normal," "no-decompression" style dive, (in which pulmonary oxygen toxicity is not a concern - in other words, that you haven't already exposed yourself to too many hours of oxygen (PPO2's)), 100% oxygen delivery will always help flush nitrogen out of your body, which in simple terms means the lowering of your pressure group. This, in theory, is a good idea.

However, in practice, it's a problem because the benefits are negligible as compared to the costs. Firstly, oxygen delivery at the surface means that you're tied to a tank and regulator of some sort. If you weren't on oxygen, you could function normally, take the time to change out your tank, discuss the dive and plan for the next one, get some munchies and Gatorade, etc... You know, all the things you normally do during surface interval. Secondly, the cost of refilling 100% oxygen (or for that matter, any enriched oxygen supply) is an expense you can not ignore. Thirdly, the benefits are negligible... You might reach a desired pressure group in 40 minutes, rather than an hour, for example. Someone with the right software will have to plug the numbers in for you to get actual times - I'm only estimating.

...So should you do it? Your call. I would recommend the simplest philosophy while diving, which includes waiting a few minutes longer on your surface interval, rather than buying the extra kit, toting it around, being tied to a tank during surface interval, and then, of course, having to refill it.

5 minutes on it? Yeah, it'd work - maybe 80% of the effectiveness as being on it your whole surface interval - but you'd still have all of the disadvantages, saving yourself only being tethered to a bottle for 40 minutes and maybe a reduction in cost. One of the reasons that it works so well in decompression diving is because you're not only breathing it, but also reducing your intake of nitrogen at depth by replacing a gas with nitrogen in it for a gas with no nitrogen in it. In short, you're better off switching to a decompression bottle - say, 50% O2 at 70' - than you are breathing 100% oxygen at the surface, after you've already ongassed the nitrogen.

Simplest way - wait it out. You'll want an hour surface interval anyway to switch tanks and all that jazz. The idea of adding 100% (and 50% is almost as effective, has a deeper operational depth, and can be had easier) really only becomes a big benefit to you at depth.

...And for that, I recommend professional training. Start with a nitrox course and move into a "technical" course where they teach staged decompression diving.

[Chugwhump]

For the most part....
Too much work for too little return in recreational diving.

Chug
Can suck O2 with the best of them.

[Akimbo]

There is a lot of related information in this thread.

Increasing Safety Margin

I suppose the simple answer is that it isn’t unheard of, but not especially common. Most dive profiles benefit more from using the O2 during an extended safety stop than on deck. Naturally, there are additional risks to this procedure and requires a thorough understanding of oxygen toxicity, safe handling of HP O2, and your Oxygen Clock.

A near-optimum Nitrox mix provides much greater benefits in recreational diving depths though. I would add pure O2 to the equation after incorporating Nitrox.

[Thalassamania]

No, your thinking is not off. Given a "normal," "no-decompression" style dive, (in which pulmonary oxygen toxicity is not a concern - in other words, that you haven't already exposed yourself to too many hours of oxygen (PPO2's)), 100% oxygen delivery will always help flush nitrogen out of your body, which in simple terms means the lowering of your pressure group. This, in theory, is a good idea.

However, in practice, it's a problem because the benefits are negligible as compared to the costs. Firstly, oxygen delivery at the surface means that you're tied to a tank and regulator of some sort. If you weren't on oxygen, you could function normally, take the time to change out your tank, discuss the dive and plan for the next one, get some munchies and Gatorade, etc... You know, all the things you normally do during surface interval. Secondly, the cost of refilling 100% oxygen (or for that matter, any enriched oxygen supply) is an expense you can not ignore. Thirdly, the benefits are negligible... You might reach a desired pressure group in 40 minutes, rather than an hour, for example. Someone with the right software will have to plug the numbers in for you to get actual times - I'm only estimating.

...So should you do it? Your call. I would recommend the simplest philosophy while diving, which includes waiting a few minutes longer on your surface interval, rather than buying the extra kit, toting it around, being tied to a tank during surface interval, and then, of course, having to refill it.

5 minutes on it? Yeah, it'd work - maybe 80% of the effectiveness as being on it your whole surface interval - but you'd still have all of the disadvantages, saving yourself only being tethered to a bottle for 40 minutes and maybe a reduction in cost. One of the reasons that it works so well in decompression diving is because you're not only breathing it, but also reducing your intake of nitrogen at depth by replacing a gas with nitrogen in it for a gas with no nitrogen in it. In short, you're better off switching to a decompression bottle - say, 50% O2 at 70' - than you are breathing 100% oxygen at the surface, after you've already ongassed the nitrogen.

Simplest way - wait it out. You'll want an hour surface interval anyway to switch tanks and all that jazz. The idea of adding 100% (and 50% is almost as effective, has a deeper operational depth, and can be had easier) really only becomes a big benefit to you at depth.

...And for that, I recommend professional training. Start with a nitrox course and move into a "technical" course where they teach staged decompression diving.

5 minutes of surface O2 is not enough to mean much. But 10 minutes of O2 at twenty feet might well be. Surface O2 can be a helpful adjunct for scrubbing out excess nitrogen, for example two hours of surface oxygen (honest 100%) will remove enough nitrogen to take you from USN Repetitive Group N down to Repetitive Group A. Some physicians will warn that the use of surface oxygen is a bad idea because it could mask DCS symptoms that will be exacerbated on a subsequent dive.

[ajduplessis]

^^^^^^
+1

[danvolker]

As Thal said, if ypu want the extra margin, buy a 20 or 30 cu ft pony bottle, get it cleaned and filled with O2, and carry it stage style like GUE divers ( clipped to left side cheast D-ring and waist d-ring) with it's own reg on it and short hose, looped and held close to the tank by a bungee or similar...
you don't need one this big though unless doing technical exposures:-)

There is NOTHING to doing this....The pre-requisite is that you must have good bouyancy skills, and be able to hold your 20 foot stop depth within 5 feet, no matter what. As this is incredibly easy for an advanced diver ( if it is NOT easy, the person is NOT an advanced diver !!!!!) , this is a great solution for you.
And 10 minutes is the right amount of time...much longer and you begin to get a form of edema from the o2 exposure......
Keep this in mind also.....O2 has a side effect..it is much healthier than to get large bubbles in your blood, and to get DCS....But if you are NOT in danger of DCS, pure oxygen, and even Nitrox at 30 to 40 % mixes, is essentially increasing the amount of free radicals your body is exposed to enormously--this is what we take Vitamin C and Vitamin E, etc, to eliminate, due to the unhealthy nature of free radicals in your body.

So pushing ther maximum oxygen exposure you can handle without toxing is not the smartest thing you could be doing :-)

[Deep South Divers]

Ulfhedinn, aside from the "free radical" theories (which only become an issue after many hours on the stuff), there's a practical issue to using 100% oxygen: The only way I know of to get 100% oxygen is to purchase it in large, 5' tall bottles from a gas supplier like Air Liquide, a supplier to the medical, welding, and aviation industries. These bottles come pressurized to 2400 psi, so in fillling off of them you'll only get 2400 psi in your first fill, then 2300 on your second, 2200 or so your third, and so on.

To combat this problem of short fills, "tech" dive shops use a device called a Haskel booster, which can repressurize oxygen to a full 3000 psi - an aluminum sling bottle's capacity. Obviously, all of this can be an expensive, complicated, and if not done right, dangerous procedure, adding to the cost of getting 100% oxygen fills.

Membrane "nitrox" systems - more commonly found these days in the dive shops - only produce O2 mixes between 21% and 40%... These mixes can be used to create trimix, if first diluted with helium, but the point is that a 100% oxygen "mix" can not be had with these systems. The net result is... If it's 100% oxygen that you're after, more than likely - if you can find it at all - you're gonna end up with a short fill. You can take this matter into your own hands, of course, and build your own system like I did, but the expense and maintenance must be considered.

A far easier solution would be a 50% mix. It's achievable by taking an empty scuba bottle and filling it off of a supply bottle to 1130 or so psi and then topping the scuba bottle off to 3000 psi. The exact numbers vary according to ambient and fill temperatures, and you eventually get a feel for it and improve accuracy. Physiologically, 50% works almost as well as 100%, is usable at deeper deptha (70' rather than 20') so that you can stay on it longer (increasing it's effectiveness), and of course allows you complete fills until your supply bottle gets to 1150 psi or so.

Regarding "slinging" a bottle: Danvoiker is right... This configuration allows you to attach and release the bottle quickly and easily while staying nicely streamlined. It also allows you full access to the regulator, so it can be stowed, deployed, and restowed without much fanfare. I would recommend an aluminum 40 for this bottle, which is the same diameter as a 20 and 30, but long enough to reach your chest and spg D-ring. Unless you're unusually short or use a long leash, I don't think you could get an AL20 or AL30 to fit.

[gsk3]

There is NOTHING to doing this....The pre-requisite is that you must have good bouyancy skills, and be able to hold your 20 foot stop depth within 5 feet, no matter what. As this is incredibly easy for an advanced diver ( if it is NOT easy, the person is NOT an advanced diver !!!!!) , this is a great solution for you.

Dan I like you but this is a bit cavalier....

Even a diver with good buoyancy shouldn't be doing this without appropriate training. What if they go OOA at depth and switch to the "pony" bottle? What if they add a second slung bottle and now they are doing gas switches at depth without knowing the gas switch procedure--if they've been carrying one bottle for years, then carrying two bottles shouldn't be a big deal, right? What if they don't mark it appropriately and someone on the boat mistakes it for their stage?

Recreational nitrox certifies you to 40% mixes. Much better idea to use those mixes you've been trained in to try to make your safety stop safer.

[M_Bipartitus]

There is a relevant article in the first issue of this online diving magazine
Tech Diving Mag | Free online technical diving magazine .

They discuss the use of oxygen to off-gas before a flight. As I recall they didn't see a very big improvement for the technical dives simulated.