33 replies to this topic

[Diverbrian]

Funny
All that and no one brought up the reason I like 80%.....
Pumpin oxygen to 3000 or 3300 psi(depending on working pressure of the tank) is getting on the more dangerous side. So...... If you pump the oxygen 2250 or 2464psi then top with air you avoid some risk in filling. Of course you could just carry pure O2 and not completly fill the tank. However if I am going to go through the effort of bringing a tank with me I want it to have as much gas in it as safely possible. This gives me more backup and more options.

That is why I use 80%(actually I use 78% that way the blender can be off by as much as 2% and I dont have to change anything.

Cheers Jim

That's why many of the people that I dive with use LP45's for stage bottles to use strictly as O2 bottles. They don't need to pump those to 3000 psi, LOL. They just don't like EAN80. After diving it, I could see why. It just didn't feel right to have wait that far into my deco to go to a richer mix than my backgas. If I was going to wait that long, pure O2 would have given me a better advantage. From now on it is EAN50 and/or pure O2 for me.

As to reg's catching fire, I have never heard of that happening, but I could see where it would. I can't envision it happening underwater, though.

Walter's right. More training is very seldom a bad idea.

[Walter]

A few years back, a titanium reg caught on fire in California.

[Diverbrian]

A few years back, a titanium reg caught on fire in California.

I knew that there was a reason that I don't use Titanium regs. Sometimes it's nice to be not be wealthy, LOL.

[TraceMalin]

Walter,

Do you know the details of the titanium fire incident? I've heard about it, but I didn't know if it was fact or urban legend. Titanium regulators often come with warnings not to use them with nitrox or oxygen mixtures.

The danger of high or pure oxygen mixtures really comes from breathing the wrong gas.

Filling is far down on the food chain of problems related to mixed gas diving. However, any fire or explosive danger is going to be present during the fill process when gas rapidly passes through the valve, cylinder threads and into the cylinder causing friction, molecular action and heating. Farther down the mixed gas food chain of events woud be the risk of combustion when cracking a valve to allow the contents to enter the first stage of a regulator. Because titanium can help with ignition, it is not recommended. But, many divers don't even clean regulators for use with nitrox or oxygen and we aren't experiencing a rash of fires. Not that it can't happen, but the chances are low. If anyone has worked with 100% oxygen in construction, you know that it is not handled gently or cleanly.

During a dive, the opposite of heating is happening. In fact, very few divers know what the commercial diving industry has known for many years and that is that a regulator freeze up is theoretically possible even in warm water due to a temperature drop inside the first stage. Divers can be subjected to pulmonary emergencies caused by cool or cold gas entering the lungs. There has been some speculation that some of the deaths on deep wrecks in cold water have been the result of a pulmonary episode brought about by breathing cold dense air or while breathing trimix in which case the helium significantly adds to heat loss within the lungs.

Quiz: Does anyone know why all of the hydrocarbons left in your mouth from breakfast don't cause your head to catch fire while you are breathing 100% oxygen from a dirty rubber mouthpiece or why your so called oxygen clean cylinder no longer really is after it is hooked up to most any nitrox compressor?

Trace

[Walter]

Sorry Trace, I don't have the details. I seem to remember it was an instructor in California and I believe the mix was around 50%. It's not an urban legend.

[TekDiveGirl]

Sorry Trace, I don't have the details. I seem to remember it was an instructor in California and I believe the mix was around 50%. It's not an urban legend.

Yes it is a true story and it was an instructor -- it happened in San Diego -- on 80% -- here is what Mike Kane wrote about it in Rec.Scuba on June 7, 2000 --
------------------------------------------------------------------------------------------
The story is true. It happened to a friend of mine. His name is John Cain
and I spoke with him yesterday in the hospital.

The 80% issue aside for a minute ( I'll get to that later ), he sounded in
good spirits but he was pretty banged up. He has 1st, 2nd and 3rd degree
burns on varying parts of his body. He underwent surgery yesterday and is
expected to be hospitalized for about a week. I'll call him tomorrow and
get an update.

But as to the facts, He was working with a bunch of open water students and
was planning on doing 5 very shallow dives with different students during
the day. He wasn't even taking the gas in the water, he just wanted to
breathe it as an extra measure of protection during SIT's. He cranked on
the bottle while leaning on the back of his truck. His arm was leaning on
the 1st stage and when he opened the valve it ignited. He was using the
Atomic T1/T2 and swears that it was 02 cleaned. The tank ( AL 40 ) was in
current hydro.

His wetsuit caught on fire and by the time he was able to get the flames
extinguished he has suffered some bad burns.

The REALLY sad part of this is several fold. John is really a great guy and
there were several other diver's in the area ( from a competing shop ) and
when John was getting into the ambulance they were heard to say that he
deserved it for diving with elevated 02 mixes. Moreover, they even went on
the local news channels that evening and continued this tirade saying that
by not diving within recreational mixes that it was his own fault. Nor did
they help when he was on fire..

As soon as I know more details about the diver's and shop I'll provide them.
It's one thing not to agree with someone's diving philosophy, but it's a
completely different matter when someone is on fire to stand around and play
Monday morning quarterback. Hell, I'd even help BLACK if he get's in
trouble this weekend ;-)

As to the 80%, John and I talked about this 3 weeks ago and John ( along
with Perry Armour ) is very involved in setting up my DIR demo in San Diego
slated for July 16th. In fact when John was in L.A. a month ago his comment
to me was help de-strokify me. While it was said TIC at the time, my sense
is whether he has 80% or 100% this may still have happened. But I did tell
him that if he were on any of my trips that I would make him blend last that
evening if he insisted on 80% ;-)

Also, he did say that all O-rings were viton. As soon as I know more I'll
update.

Regards
-----------------------------------------------------------------------------------------

So there ya go! No urban legends there! (-;

[maninthesea]

To add a little Mares hinted about this incedent when they announced they were changing the seat material in their titanium reg from titanium to Stainless. They have since discontinued the reg completely.
Jim

[TraceMalin]

Okay, one amazing story proven true! And, wouldn't you know that one of my GUE instructors was connected? MHK!

I guess I'd better O2 clean my stage regs, huh?

Now... what does anyone know about that diver found in the woods? (this is when I'm kidding, Peter)

Trace

[TekDiveGirl]

Now... what does anyone know about that diver found in the woods? (this is when I'm kidding, Peter)

..... and this one time.... at band camp....

[peterbj7]

Oh, you're talking about the diver who was scooped up by a fire fighting aircraft and dropped into the middle of a forest fire. Didn't do him a lot of good, as I recall.

[Marvel]

Oh, you're talking about the diver who was scooped up by a fire fighting aircraft and dropped into the middle of a forest fire. Didn't do him a lot of good, as I recall.

No way, Peter! Tell us more?

[bigblueplanet]

I had a monster post for this string, but my computer crashed dumping it all. So, I am not going to go deep on this one, but there are several things on this.

The San Diego incident did happen as was posted. It was actually 87%. But, that does not matter. It could be 100% or 60%, it likely still would have happened. The moral to the story, oxygen cleaned or not, DO NOT use titanium or aluminum first stages with any mixture over 40%. Titanium will burn in one tenth of an atmosphere of oxygen when ignited and burn till the oxygen is gone or the material is. His mistake was the use of a titanium first stage. The mixture had nothing to do with it other than it had the high mix. The metal was the problem. Review NASA White Sands info or better yet take their class and you will have a very good understanding of these issues. Over 40% mix, use brass!

Now, as to the question of 80% specifically. It is used to excellerate decompression. Known in some circles as stroke mix, for those who have caught the cancer. But, in reality there is little reason to use it. Pure oxygen is simplier to blend, provides zero inert gas and logistically is simple.

Filling oxygen is a risk that is not way down the list. We just had an oxygen related explosion in Lauraville in Florida at pressures below 2000 and at the initiation of filling into a partially filled oxygen cylinder that was cleaned for oxygen service. So, it does matter. But, with good procedures and training it is a safe thing to do. Filling oxygen to 3000 is not any more dangerous that above 2000. With the proper gear it is safe. That is an old wive's tale.

For those who use 80%, yet switch to it at 30 feet, I ask would you rather have an oxygen issue at 30 or at 20? For those who use 80% at 20 because you do not want to have the high PO2, Then why not just use pure oxygen at 15?

The computer will show you almost no change in deco with 80%, but still having inert gas in the mix is not the same as pure oxygen. With pure oxygen, you have zero inert gas in the lungs. You are going to create a drive pressure to pull more inert gas to the lungs than any other way. Plus, I think it is just more partical and the deco feels better.

If you do not think you can maintain a stop on oxygen at 20, then stop tech diving. Even if the surface is eight feet swells, you must have the skills to hold stop depth plus of minus a foot. Besides that, oxygen is a time dose response. A small deviation is not going to cause a seizure. It is good to be worried about oxygen, but it is far simplier to keep PO2 down on the bottom so you can up it on deco. Better to do it on deco than try to get a minute more on a richer bottom mix.

This question is about deco. No matter what model you use, the idea is to maximize the efficency of whatever deco you do. In fact, it looks like it is better to excellerate deco and get out of the water sooner, than to do a bunch of extra deco from a physiological stand point. RGMB and VPM are gaining popularity, but for recreational diving all the models are so close it provides almost no effective difference.

For technical diving RGBM and VPM provide profound differences with time and approach. They do require very good skills, but as was said before, you should not be tech diving if you cannot manage the skills needed. These models do require high oxygen on deco. It is built around excellerated deco, thus requires oxygen on deco. There are ITs out there training people to use only 60, 50 or 70% for their rishest deco gasses and people are getting bent. So, if you are going to use these please learn and know what you are using. Do not trust what is told to you by even an experienced instructor unless it lines up with what makes sense and what other sources give.

The moral to the story for the recreational diver is that you should plan your dives with multilevel ascents with delays at half depths and do safety stops. If you are trained use oxygen at 15 feet. Or at the surface. This can be very useful for instructors after ascent training. No model in the world can account for that behavior. I believe we posted a long string on safety stops on another string.

So, 80% is used to try to excellerate decompression. Opinion flag... No reason to use it. Use pure oxygen. It is just easier, better on the oxygen window. Venous blood gas pressures are better with it. 80%ers, you can mix it for the whole of an expedition, we will wave to you when we head off to dive the next day as you are still finishing the mixing from the night before. Find old HJ 72s, they make great oxygen stages. Near neutral, full at 2400 and good buoyancy characterisitcs.

Take breaks to check the clock and reverse vasoconstriction. Train, train and train some more. You are never done. Just when you think you might have it, another door opens and a whole world is left to learn about.

Guess it still ended up a long one. Way more to all this than the sum of all these posts. Hope my two cents contributes.

Grant

[Marvel]

Thanks all for the posts & explanations. Grant, the safety stop issue was discussed so very well in this thread : Timmy's in the well, How fast should he ascend?- great tie in & it is now making much more sense to this :marvel: & I'm sure to others as well. Interesting that you propose accelerating deco but we are addressing the use of stage bottles which, as recreational divers, most of us don't use. I found Walter's suggested slow ascent rate to be very logical & have pretty much adopted that in my diving as an alternative. And, since the majority of my diving is done in my side yard with a max depth of 20 feet, surfacing near the shore, even my ascents from most of those dives is very gradual beause I am going in to the shore. Still food for thought & you've all increased my desire to master shallow depth bouyancy, which, IMVHO, is the most difficult area of buoyancy to control. The end result, I hope, is that many more of us now understand the WHYS of the 80% mix & the logic of the 100% that was advocated earlier in this thread.

[bigblueplanet]

Review the old thread. Slow ascent rate is good to a point, but adding safety stops is better. It is better to do a safety stop and add a deeper one and ascend at the computer's rate than to dramatically slow ascent and not do the safety stops. Even really slow to a single safety stop is not as good as a shallow and deep stop with controlled ascent rates. The data is clear that super slow linear ascents as not as good as ascents at faster rates with stops. FYI

Yes, the total key is shallow water buoyancy and it is by far the hardest because it is the place of greatest expansion of gas. So, things change the fastest. You need to be more on it. I have begun to keep open water students in the shallow end and work nothing but breathing and buoyancy for two hours at the very beginning of the course. The shallow end of the pool is the best place to lock and load good technique. It is where everyone should go when they have changes to work into their diving or have been away for a time. Take it shallow and work it to depth. Instructors, try this on your next open water course. Do what you need to do to get the breathing in the shallow end and then do nothing but work breathing and buoyancy work, only in the shallow end for two hours. Bet you the rest of the course is easy and you finish the skills in less time, leaving more time for more practice. Train them how to think like an elite diver from day one. Build the mindset and the skills will follow because they will know they are never done.

It works. Easier to establish a good habit the first time than fix a bad one later.

M, go back and look at the buoyancy string as well. A ton of good stuff there too. I think it is in dive training.

G2

[Diverbrian]

Review the old thread.  Slow ascent rate is good to a point, but adding safety stops is better.  It is better to do a safety stop and add a deeper one and ascend at the computer's rate than to dramatically slow ascent and not do the safety stops.  Even really slow to a single safety stop is not as good as a shallow and deep stop with controlled ascent rates.  The data is clear that super slow linear ascents as not as good as ascents at faster rates with stops.  FYI 

Yes, the total key is shallow water buoyancy and it is by far the hardest because it is the place of greatest expansion of gas.  So, things change the fastest.  You need to be more on it.  I have begun to keep open water students in the shallow end and work nothing but breathing and buoyancy for two hours at the very beginning of the course.  The shallow end of the pool is the best place to lock and load good technique.  It is where everyone should go when they have changes to work into their diving or have been away for a time.  Take it shallow and work it to depth.  Instructors, try this on your next open water course.  Do what you need to do to get the breathing in the shallow end and then do nothing but work breathing and buoyancy work, only in the shallow end for two hours.  Bet you the rest of the course is easy and you finish the skills in less time, leaving more time for more practice.  Train them how to think like an elite diver from day one.  Build the mindset and the skills will follow because they will know they are never done. 

It works.  Easier to establish a good habit the first time than fix a bad one later.

M, go back and look at the buoyancy string as well.  A ton of good stuff there too.  I think it is in dive training.

G2

Our instructors do just that. One session is completely spent in the shallow end for the reasons that you mention. If you can get neutral buoyancy down in the shallow end, it is far easier elsewhere. If the buoyancy is easier to maintain, then skills naturally follow.

Thanks for the insight!

PS even better is a slow ascent with the stops . Yes, the data is pretty conclusive that slow ascent rates alone are not as good as doing safety stops and ascending SLOWLY as possible from 15-20 ft.

Edited by Diverbrian, 19 November 2004 - 12:10 AM.