40% O2 mix at the safety stop

[Web Monkey]

The problem is that a rec diver who's been skip-breathing the entire dive, has a sicked headache, and comes up to a tank of 100% oxygen with a long hose, switches to that tank and sinks to the depth of the hose (now at almost 30 fsw). This diver is has a buddy that is nowhere to be found and is incapable, anyway, of dealing with a diver that is having a seizure. Get the picture?

I'm probably missing something, but why would someone put 30' of hose on a hang reg with a 13' MOD (20' if you're feeling lucky) and leave it out for OW divers?

Terry

 

[RiverRat]

I'm probably missing something, but why would someone put 30' of hose on a hang reg with a 13' MOD (20' if you're feeling lucky) and leave it out for OW divers?

Terry

They might be refering to total hose length, you know from the tank in the boat, over the side and down. That sounds about right. Yeah you got problems if you rip the rig right off the boat and start dragging it down deeper

 

[OBXDIVEGUY]

On a total side bar, I'd like to ask a question cuz it seems everyone that will be able to answer it is in this thread already:

Will/Can a tech dive shop fill a medical oxygen cylinder? ie. FillExpress in Pampano. I'm looking at outfitting a boat with an emergency kit. I have current EMT certification, so I'd guess that would suffice?

 

[String]

Medical O2 i think has a higher moisture content and maybe a tiny bit of CO2 whereas diving doesnt.

We use the same stuff here for diving and O2 first aid though (100% pure o2) which any dive shop can get.

 

[Thalassamania]

Actually I was thinking (in this case) of a hang tank at 20 with a 7 foot hose. This is not an unusual procedure for somewhat unusual dives.

 

[nereas]

So I have a question, years ago I use to dive with a friend/instructor and when he took groups of friends out on his boat we would always hang a bottle at 20 feet with a 40% O2 mix (might have been even higher-don’t recall). He said it was there for us to use at our safety stop if we wanted to. Some of us would be diving NITROX some air but no one would necessarily be breathing the same % as the safety bottle.

I know zero about planning a dive when you use different mixes (if such things are even allowed). I asked him about O2 toxicity and how to calculate it seeing how I would be going from a 32% mix to a 40% mix at the end. He told me it wasn’t an issue as long as you weren’t pushing the limit anyway (which you shouldn’t). He said the extra O2 at 20 feet for 3 to 5 minutes was mathematically insignificant. He claimed the benefit was that you off gassed more nitrogen at the safety stop. (I can see this benefit as you would be breathing in less nitrogen so I suppose that is correct)

Of course, he wasn’t suggesting that you change you dive plan; he said it just added an extra margin of safety and that personally, he always felt better when diving like this.

So the question is, was this a good idea or an accident waiting to happen? I like having the staged bottle but I am not sure I like having a different mix in it.

It would make more sense to use the EAN 40 in your tank during the actual dive, rather than use it as a hang-tank during your safety stop.

Any level of O2 higher than 21% in a hang tank will indeed give you some added off-gassing than plain air. But the difference, for NDL diving, is rather insignificant.

So your friend had good intentions, however his math was way off. The main benefit of a safety stop is to give your bloodstream a chance to scrub your body of compressed nitrogen, before your return to surface pressure.

The safety stop itself is much more significant than whatever is in the hang tank.

If you use EAN 40 in your tank, then you should not dive deeper than 100 ft.

And with EAN 40, if you drift down to 130 ft, then you would be dangerously close to experiencing an oxygen toxicity siezure. And any deeper than that and you would probably die. So you need to be careful about what you are doing when you have EAN 40, or any other nitrox, in your tank. They teach you all about this in a nitrox class.

 

[hypertech]

Some people are quite capable of learning even very complex physical tasks from a book, but others are not. We live in a culture that tends to reduce everything to the least common denominator, e.g. link.

Can't follow the link, but I'm, interested so what was it about.

No offense, you are right, you grossely (sic) misunderstand the task here. You have got it backwards: understanding the parameters of 02 tox etc, can be done by study; learning to maintain 20' maximum floor while handling a multitude of tasks (eg: the gas switch for starters....) is not something you can learn from a book. I have yet to see a new diver be able to hold a 20' stop (not 25' not 15' and definitely not 30'...) for longer than it takes to pass through it. This may seem like a rudimentary skill, but for those who haven't mastered it, it is far from as easy as falling off a chair. (speaking from experience here) A diver with a minimum of experience will be incredibly task loaded just trying to maintain position in the water column (in Cold water, it is much, much more difficult) and adding any task effectively uses up a good portion of the bandwidth available to a new diver they were using to maintain their position. Now lets make the penalty for failing to maintain this depth and maintain an awareness of where they are in the water column an 02 hit, convulsions, and most likely drowning. That is the reality of the downside of the lack of skill we are playing with here. There are several reasons why any good tech instructor teaches the critical components of a dive (gas switch definitely being one of them) in shallow water: one of the most important is that maintaining buoyancy control in in the first 2 ATA's if more difficult than in depths below that. Mistakes in buoyancy control are rapidly amplified and your ascent or descent takes on a geometric progression: IE, your descent or ascent accelerates, further accelerating....etc. A friend was teaching two students to do valve drills and when asked if they were comfortable holding buoyancy in 20' of water, they said yes. They were beside a 80' wall and they started their valve drills at 20'. My friend finally grabbed them and told them to cut the drill as they were descending past 60'..... the point being that they were so task loaded that they lost track of their buoyancy for a few seconds and things rapidly escalated. These two students were experienced divers new to tech. Now imagine if that had been a gas switch to 02..........what do you suppose would have happened by the time they hit 60'...or deeper? 02 hit? Don't know for 100% but if I was a betting man...........

As far as the flying thing goes, speaking as someone with several hundred hours in F-18's, I am really damn glad I didn't just learn a lot of that from books......

I won't buy into the argument that bouyancy control is a tech skill. I will buy into the argument that people who don't have the skills to do something shouldn't do it.

I don't think there is anything about this that requires tech training. The requirements are pretty simple: did you have a conservative dive, are you above 15-20 feet, can you maintain your depth at 15 feet adequatly when next to a line and or a hose anchored to the boat? Can you change your reg without freaking out (after all, breathing from alternate air is an open water skill)? If the answers to those questions are yes, then you can decide if you want to grab that reg or not.

 

[nereas]

On a total side bar, I'd like to ask a question cuz it seems everyone that will be able to answer it is in this thread already:

Will/Can a tech dive shop fill a medical oxygen cylinder? ie. FillExpress in Pampano. I'm looking at outfitting a boat with an emergency kit. I have current EMT certification, so I'd guess that would suffice?

A good dive shop, which has oxygen, can fill those, yes.

But they will want to see from you either (1) a DAN oxygen provider card or (2) a stage deco card, showing that you are at least some kind of trained tech diver or oxygen provider.

 

[nereas]

Can't follow the link, but I'm, interested so what was it about.

I won't buy into the argument that bouyancy control is a tech skill. I will buy into the argument that people who don't have the skills to do something shouldn't do it.

I don't think there is anything about this that requires tech training. The requirements are pretty simple: did you have a conservative dive, are you above 15-20 feet, can you maintain your depth at 15 feet adequatly? If the answers to those questions are yes, then you can decide if you want to grab that reg or not.

Nitrox training allows dive shops to fill tanks for divers up to EAN 40. This is not normally considered tech training. So you are quite right about that.

Advanced nitrox training allows fills to 100%. And this is normally considered a part of tech training, the start of it, in fact.

Without the training, and proof in the form of the C-cards, a responsible shop won't give out the fills, or shouldn't, as everyone knows.

 

[String]

Without the training, and proof in the form of the C-cards, a responsible shop won't give out the fills, or shouldn't.

Fortunately most of the rest of the world other than america doesnt insist on nannying and allows people to make their own choices so cards aren't needed.