50 replies to this topic

[PerroneFord]

Ok,

Let's dispell some rumors here.

1. There are generally only 3 places that will see high pressure gas with a high oxygen content. They are the tank, the first stage, and the SPG/dive computer on a hose. If you are diving with Nitrox percentages over ~40% these must be prepared for use with that kind of mix.

2. Many shops blend nitrox "in the tank" meaning they put pure oxygen in your tank and then put in the air on top of it. This is called partial pressure blending. If ANY shop you use to fill your tank does this, you must have your tank cleaned to accept oxygen.

3. If you tank your previously cleaned tank, that was prepared for oxygen, and you fill it with air that is NOT "oxygen compatible", meaning it is not filtered to a very specific level, you must re-clean the tank. The danger here is not to the diver. The danger is to the fill station operator.

4. BCDs, second stages, etc., are seeing low pressures of the mix, and since it is already diluted by the time it gets there, there is nothing to worry about. This is not true with titanium.

Now, hopefully, everything is as clear as mud.

[Indydivegal]

Hmmmm,

So can't use nitrox below 110 eh? Alrighty.

Might want to be cautious using those titanium regs around enriched air nitrox, they don't mix well at ALL.

I have also been "warned" that the titanium Regs are not a good mix with Nitrox. Good advice!!

[annasea]

<snip>

So, be careful the mix you use when you dive nitrox. And yes, it can be taken below 100 or even 110ft. I dove nitrox on the Oriskany at nearly 125ft, and could have gone to the deck at 135.

<snip>

So what mix (%) were you using when you dived the Oriskany?
Since Nitrox is not recommended for such depths, how were you able to dive to 125' safely using it?
Would something like Trimix be better suited to these types of depths?
(Side note: Doesn't drbill dive in the 180' range on air?)

[PerroneFord]

So what mix (%) were you using when you dived the Oriskany?
Since Nitrox is not recommended for such depths, how were you able to dive to 125' safely using it?
Would something like Trimix be better suited to these types of depths?
(Side note: Doesn't drbill dive in the 180' range on air?)

Who says Nitrox isn't recommended at those depths? Works great as long as you understand how to use it. Trimix would be more effective, but for a different reason.

And I certainly won't be following Dr Bill's lead and diving air that deep. In fact, I don't use air at all underwater, but that's a personal choice.

[annasea]

Who says Nitrox isn't recommended at those depths? Works great as long as you understand how to use it. Trimix would be more effective, but for a different reason.<snip>

So how does one uses Nitrox differently than air in order to ensure one's safety? What is the "different reason" that Trimix would be more effective than Nitrox in your Oriskany situation, for example? (I'm trying to get a *real life* overview of the gases, their applications and their differences.)

[shadragon]

I would be interested to see who is voiding their warrenty when using nitrox with their gear.

The Suunto Equilite BCD specified in their manual to not use it with enriched air. Not only that, but that it would be "dangerous" to do so. I tried to find a copy of it on-line, but came up blank. I read that manual just as I was starting to look for my own gear a few years ago. One of the students I was on my OW with had one and showed it to me, while laughing about it... I also have a no name BC hose mounted air horn that said it should not be used with Nitrox. Small print in the back of the manual. There is usually a catch all phrase that says if you use gear beyond design limits there is no warranty coverage.

It is the same with computer EULA's (End User License Agreements). Some of them are right out to lunch.

Silly EULA Example

PS. As this is a tech diving thread I automatically assumed the gear in question would be subjected to > EAN 40. < EAN 40 should be fine, but again read your small print to make sure.

Edited by shadragon, 27 February 2007 - 12:30 PM.

[matts1w]

When diving nitrox we are concerned with the partial pressure of oxygen. Most like to keep that number less than 1.4, but some will push the number to 1.6. That is, of course, up to the individual diver and/or how they choose to dive, but most agencies stress keeping the ppo2 under 1.4 to be safe and conservative. Most believe diving with a mix over 1.6 ppo2 risks the convulsions Perrone spoke of earlier.

There several simple formulas to determine this based on the depth and mix. I can determine the ppo2 of a mix at any depth with one formula. Another is the maximum operating depth (MOD) formula. There is also a best mix formula. If I wanted to dive a wreck to 135 I could use any of these formulas to determine what would be the best mix of nitrox for the dive.

For instance if I had a bottle of EAN27 I could determine the MOD at 1.4 ppo2 is about 138 feet. I would feel comfortable diving that mix to 135 feet, but some may prefer an ever more conservative mix.

If I had a bottle of EAN32 and wanted to make a dive to 135 I would be way over the 1.4 ppo2 guideline. In fact, I would be a few feet over the 1.6 ppo2 contingency planning limit. To me pushing 1.6 is too much, but I will dive over the 1.4 ppo2 range when doing my own dives. That is a choice I make and goes against what many people and agencies reccomend.

The limits you mention are based on the mix and, to an extent, the personal risk one is willing to take for the benefit of taking on less nitrogen and extending bottom time a bit.

Edited by matts1w, 27 February 2007 - 12:34 PM.

[Diverbrian]

Who says Nitrox isn't recommended at those depths? Works great as long as you understand how to use it. Trimix would be more effective, but for a different reason.<snip>

So how does one uses Nitrox differently than air in order to ensure one's safety? What is the "different reason" that Trimix would be more effective than Nitrox in your Oriskany situation, for example? (I'm trying to get a *real life* overview of the gases, their applications and their differences.)

A diver takes great care that the maximum operating depth of their mix is not going to be a problem. Then they use the lesser amounts of inert gas to gas to allow them longer bottom times, shorter decompression, or shorter surface intervals.

To be honest, I use a 30 or 28 percent mix to to 125 ft. to lower the chance for an oxgen toxicity hit. That is my choice. I don't get quite as much of the other benefits, but in cold water it is not a good idea to play games with oxygen toxicity.

I won't get into actual numbers on this thread, but another couple of percent of oxygen would be indicated for decompression stops where one is at rest (another factor that helps prevent an oxygen toxicity hit).

Trimix would be more effective for one reason. The helium would cut down on the chance of being affected by nitrogen narcosis. That can become a real factor starting at about 100 ft. The reason that trimix involves so much more training is because it goes into and leaves the blood more quickly than nitrogen. Therefore, your decompression will accrue more quickly and require more precise stops than if the diver is using a nitrox mix. The benefit is being able to think more clearly at depth.

[matts1w]

So how does one uses Nitrox differently than air in order to ensure one's safety?

Nitrox is really no more safe than diving with air. It is a tool to extend bottom time, aid decompression, and benefit surface intervals to an extent.

Edited by matts1w, 27 February 2007 - 12:39 PM.

[Moose]

The limits you mention are based on the mix and, to an extent, the personal risk one is willing to take for the benefit of taking on less nitrogen and extending bottom time a bit.

Hum, this made me think of a scenario. Maybe one of you long time Nitrox guys can answer.

Ok, you and your buddy are diving on nitrox mixture with a max depth (1.6) of 120’. You are on the side of a wall with the ocean bottom at about 180’. You have a pony filled with normal compressed air.

You look at your buddy something is wrong and they are going down past 115’. They keep falling past 120’.

Could you, remove your nitrox reg, take your pony reg, go down to 130’ to get them, then, once above 115’ put the nitrox reg back in?

Again, I’m only talking about an emergency situation where the other choice is to let your buddy go (you can’t follow them with your nitrox.)

[Dive_Girl]

To be honest, I use a 30 or 28 percent mix to to 125 ft. to lower the chance for an oxgen toxicity hit. That is my choice. I don't get quite as much of the other benefits, but in cold water it is not a good idea to play games with oxygen toxicity.

[PerroneFord]

Could you, remove your nitrox reg, take your pony reg, go down to 130’ to get them, then, once above 115’ put the nitrox reg back in?

Again, I’m only talking about an emergency situation where the other choice is to let your buddy go (you can’t follow them with your nitrox.)

Could you do it? Sure. Could you do it without changing onto the pony? Probably. It's not like there is some fine line that says if you exceed 1.6 you'll immediately convulse. Some people have pushed 2.0, and even 3.0 for short periods without issue. Maybe they do it 99 times. But the exact same dive on time 100 causes them to convulse. It's a huge guessing game when you push the edge.

Now, I will say this. If I was going to be over a 180ft bottom, I'd carry a mix that was safe (1.6) for 180ft. I tend to mix for the sand more than I mix for intended depth. On my orisikany dive, I mixed for the flight deck. I intended to stay above 100ft, but ended up going to 121ft. My mix was safe to 135. Even at 121ft, working against the current, and trying to keep up with the moron dive captain, I was beginning to get feelings I didn't like. So I slowed down my pace and decided I'd solo before I'd try to follow Capt. Ahab.

Increased work rate or stress can magnify the effects of oxygen toxicity. Again, the published numbers are guessing games. I know many rebreather divers who dive with a PP02 of 1.0 or maybe 1.2. They back off to be on the safe side.

For recreational diving, a 32% mix should take you nearly anywhere you want or need to go. And a 36% mix for shallow reef diving is awesome.

[echo3]

Ok,

Let's dispell some rumors here.

.....

4. BCDs, second stages, etc., are seeing low pressures of the mix, and since it is already diluted by the time it gets there, there is nothing to worry about. This is not true with titanium.
....

well, I just looked and my BCD (Mares) is not nitrox compatable

[PerroneFord]

I'd bet all the money in my wallet right now that is is. I absolutely HATE when companies take this CYA stuff this far.

Edited by PerroneFord, 27 February 2007 - 02:24 PM.

[echo3]

I'd bet all the money in my wallet right now that is is. I absolutely HATE when companies take this CYA stuff this far.

how can I be confident & safe ?

MARES supplies its authorized dealers with a kit for converting MARES BCs for use with oxygen rich mixtures (Nitrox - maximum oxygen content: 40%). If, after the conversion, the BC is used with normal compressed air, it will be necessary for a trained MARES technician to repeat the entire conversion procedure before using the BC with oxygen-rich mixtures again. This is because the BC may be contaminated with traces of hydrocarbons or other impurities which could spark combustion.

WARNINGMARES BCs are designed and constructed exclusively for use with compressed atmospheric air. Do not use this MARES BC with other gases or with oxygen-rich mixtures. Failure to observe this warning may result in premature wear of the equipment, defective operation or risk of explosion, resulting in potentially serious damage. The conversion of a MARES BC for use with oxygen-rich mixtures must be carried out exclusively by trained and qualified technicians who are perfectly familiar with all the cleaning and assembly procedures for high pressure oxygen systems (with oxygen content exceeding 21±2%).

right out of the manual for my BCD