29 replies to this topic

[peterbj7]

I agree with Brian that the issues raised in the sad accident reported under "news" should be considered more generally.

This case demonstrates that correct filling procedures are essential, especially when dealing with manifolded twinsets. Even if proper checks are carried out by the diver (they seem not to have been in this case) it is not always possible to be sure what there is in each tank. As Brian (?) says, once the tanks are filled to the same pressure there will be minimal mixing through the manifold.

If poor filling techniques have been used and CO has gotten into the tank, there is in practice no way the diver can tell before going down with it. It can theoretically be detected, but those tools are not routinely available to divers. And of course CO has no taste or smell, so that doesn't help. The effect of CO on the body (as with all gases) is dependant on its partial pressure, which of course increases with depth - what is perhaps not detectable at the surface may cause a headache after a while at 20 metres, and may kill at 60 metres.

Incidentally, this highlights one reason I am so against SNUBA - the exhaust of the gasoline compressor is necessarily pretty close to the breathing air inlet, and in any conditions other than a steady moderate breeze it seems to me all too easy for fumes to be sucked into the inlet.

And of course, in an emergency at depth it is essential to be able to offer a gas that is breathable at that depth. Another reason for techies breathing from their long hoses, as the reg they're using is the one a OOA diver is most likely to grab, and it's easiest if that has a long hose so no further switching is needed.

Learning from this recent accident but going beyond it, what are people's thought on the general issues, both for yourself and someone you may encounter underwater?

And the topic title should have been "Breathing baD gas....."! Goodness knows what baG gas is. But I can't change the title.

Edited by peterbj7, 05 October 2005 - 12:50 PM.

[cmt489]

And the topic title should have been "Breathing baD gas....."! Goodness knows what baG gas is. But I can't change the title.

Ahh, but I can...

[PerroneFord]

I was kicking this around with a friend of mine last night. He pointed me to a photo of the IANTD Deco Sticker. For those of you unfamiliar with it, in HUGE lettering it states DECO USE, has a huge IANTD logo, etc. In small print, it has the actual MOD and tank contents. I think this is indicative of what is wrong with what I see as agency approach to technical diving. PADI and other organizations are teaching Deep Air still.

I am only familiar with the gas switch procedures of one training agency. They advocate labeling ALL non-backgas tanks with ONE thing. MOD. Because in truth, that's all you really care about. And they label them in 4" high letters on both sides of the tanks. You can see it, and so can your buddy/team. All regs are parked with the gas off other than backgas (or travel gas if you are using it). At switch time, the reg is retrieved from the appropriate bottle, and the gas is turned on. The gas is then turned on, and the reg placed in the mouth. If you can breathe, you've got the right one. To me, this makes sense. I don't care if my bottle has EAN40 and your's has EAN36. If we are both above MOD for our bottles, they are safe to use. If we are below, they are not safe. Period.

I am also mystified that people who would dive to depths where their deco bottles might be lethal, would not own an O2 analyzer. And not use it on EVERY dive on EVERY tank. Particularly those diving to depths where oxtox is a real issue. Get this one wrong, and you'll likely be dead. Analyze the tanks. Sure the analyzer is $499 or more. So what? A trip to the hospital is pretty expensive too, and a trip to the morgue is awfully expensive.

I'm talking out of my neck here because it will be many months before I need to worry about gas switches and deco. I am just an OW diver. But, it doesn't take a rocket scientist to know that NOT checking tank contents on these dives is a recipe for disaster. Everything about the Eagle's Nest incident smacks of piss poor procedures, complacency, and hurried diving. These kinds of mistakes are easily avoidable when due care is shown.

Just my $.02

[drdiver]

Reliable, relatively inexpensive CO detectors for tanks can be fitted fairly easily. There's a thread about this on another forum. If someone would like the link, PM me.

[Diverbrian]

Also, my Analox O2 analyzer which seems to be used on every trip by someone only set me back $300.00 or so. Well worth it for piece of mind.

Honestly, I understand the labeling procedures on the tanks, but I don't keep my deco bottles quite that clean. As long as I know the gas that I am breathing, that is what is most important to me. My O2 bottle has huge green sticker that says OXYGEN. If anyone is diving with me, they should be aware that I won't be picking up that reg until I hit 20 ft. Also, it has a SeaCure mouthpiece. I will know by the feel of the reg in my mouth that it is O2.

My other deco bottles have the hand-written MOD in big enough letters that anyone can see them. Again, my "travel bottle" uses a different mouthpiece than either my backgas regs or my O2 reg. I use black sharpie on white duct tape and cover it with clear packing tape to prevent the ink from running. All doubles are labeled at the shop as I have other concerns about the mix in my doubles.

In any case, an O2 analysis will at least tell you if you have a severely hypoxic or hyperoxic mix. That is fastest way to tell that there is a problem if you are dealing with EAN mixes. BTW, the only time that I have forced a shop to reblend my gas was when they screwed up one of my tanks and gave me 14 percent less O2 than I asked for. If I had trusted the shop, I may have had a problem.

As to the CO situation, I have never analyzed a tank for it (my bad) but recognize it as a possibility in a shop with a poor compressor set-up. I was taught to "taste" my breathing gas before diving with it. (I pre-breathe my regs to test function. During this, I will try to see how the gas breathes.) Typically, the CO situation will have residual oil with it as well. I have also heard of valve parts breaking down and leaving fluorine in the tank. That doesn't "taste" too good . Dr. Diver is correct about the use of a CO analyzer though. It is not a bad idea.

[drdiver]

Good post. Thanks!

I have also heard of valve parts breaking down and leaving fluorine in the tank.

Do you have any more info on this? I've had some "feelings" about this, but no proof.

[Diverbrian]

Good post.  Thanks!

I have also heard of valve parts breaking down and leaving fluorine in the tank.

Do you have any more info on this? I've had some "feelings" about this, but no proof.

The description of the incident came from a TDI tri-mix instructor out of Brockville, ONT named Steve Lewis (better known on some boards as Doppler). I was discussing different things with him at Gilboa Quarry in Ohio where he does many of his preliminary dives for classes and this issue was mentioned when I mentioned the reluctance of my shops to boost O2.

He mentioned that this happened to one of his students and that the student didn't "taste his gas". That student got a rude lesson on his deep deco. The two lessons:

1) Try to not to overpressurize O2. (but there is no proof that this was the cause of the tank contamination).

2) Always taste your breathing gas as you never can predict what might wind up in it. We don't know everything and what we don't know can severely hurt us.

I hope that helps.

Edited by Diverbrian, 05 October 2005 - 10:55 PM.

[drdiver]

That's good advice. I think a lot of us assume things. and u know what that makes.

Thanks. Just like food, it is tastes bad, don't breathe it--or eat it!!

[Diverbrian]

As well, Peter said it and I will say it. If your buddy is having trouble at depth and looks ready to go unconscious or is suddenly violently ill, consider donating your gas and doing an air share. If they have contaminants in their tank and you don't, their gas will be dangerous to them and yours may save their health/life.

If they perk up, ending the dive and doing a gas share ascent is likely a marvelous idea. This is one reason that the first reaction to an unconscious diver is to try to get your primary into their mouth, not re-insert their primary. You should likely consider that their gas may be the problem until proven otherwise.

[BradfordNC]

PADI and other organizations are teaching Deep Air still.

how is "deep air" any different than regular air?

do i have to go to a special shop to get "deep air" ??

are the fills more expensive?

can you breathe "deep air" only at depth?
do you need a travel gas until you get to depth?

what happens if you breathe it during shallow dives?

[peterbj7]

Good one, Brian. PADI long since dropped mandatory shared air ascents where the same second stage is swapped to and fro, the reason being given that the process of sharing was more likely to give a major problem than whatever alternatives were available. Perhaps that's the right call at that level, I don't know. But at more advanced levels it's a skill that had better be learned and learned well. It might be that there is only one regulator (second stage) capable of delivering breathable gas, in which case you've got to share it and you've got to ascend with it. If you're in a restricted environment such as a cave it becomes enormously more difficult, but still achievable if there's no alternative. It's certainly a technique that should be included at Adv EANx level.

One further point on making regulators and the gas they give access to, identifiable by feel. I don't know if you remember when I owned up a few months ago to a serious cock-up on my part which could have ended my diving career and a lot more besides. It related to failing correctly to identify a gas, but not when I wanted to breathe it directly - that second stage was properly identified - but when I wanted it to be available to a hose I was going to plug into my rebreather. That hose wasn't uniquely identified and I got it wrong. It will always be uniquely identified in future.

[peterbj7]

Reliable, relatively inexpensive CO detectors for tanks can be fitted fairly easily. There's a thread about this on another forum. If someone would like the link, PM me.

I'm very interested, and I suspect quite a few others will be as well. Can you post the info publicly?

[peterbj7]

PADI and other organizations are teaching Deep Air still.

how is "deep air" any different than regular air?

do i have to go to a special shop to get "deep air" ??

are the fills more expensive?

can you breathe "deep air" only at depth?
do you need a travel gas until you get to depth?

what happens if you breathe it during shallow dives?

"Deep Air" isn't a substance, but a technique. It's using air as your main ("bottom") gas for dives below the recreational limit of 130' but still above the safe air limit of around 200'. Actually, most people choose to make the lower limit shallower than that, to reduce the effects of nitrogen narcosis, and resort to trimix below maybe 170' or even shallower. Depends how deep their pockets are. "Deep air" is virtually always decompression diving.

With "deep air" it's customary to use a twinset, as otherwise your dive would be very short, and to carry a rich nitrox mix to switch to once you get shallow enough on your way up, so as to reduce the length of your decompression. So you have to learn both how to carry and manage more tanks, but also the disciplines related to gas switching that Perrone's referring to.

Since your main gas is air and that's breathable at the surface, there's no need for a "travel gas". Although you could carry two different nitrox mixes and switch to each at the optimal depth, you'd normally only carry one. Typically that's 50% oxygen, though I sometimes use 80% and I have used 36%. Depends on the circumstances and how long the deco will be. Calculating your gas consumption for each gas you're carrying, and if you're diving with a buddy doing the same for each of you and combining the results to see how much gas you should be carrying to complete your dive safely, is one of the principal skills learned in courses such as IANTD Advanced Nitrox. A course I can't recommend too strongly for any serious diver.

[BradfordNC]

"Deep Air" isn't a substance, but a technique. It's using air as your main ("bottom") gas for dives below the recreational limit of 130' but still above the safe air limit of around 200'. Actually, most people choose to make the lower limit shallower than that, to reduce the effects of nitrogen narcosis, and resort to trimix below maybe 170' or even shallower. Depends how deep their pockets are. "Deep air" is virtually always decompression diving.

With "deep air" it's customary to use a twinset, as otherwise your dive would be very short, and to carry a rich nitrox mix to switch to once you get shallow enough on your way up, so as to reduce the length of your decompression. So you have to learn both how to carry and manage more tanks, but also the disciplines related to gas switching that Perrone's referring to.

Since your main gas is air and that's breathable at the surface, there's no need for a "travel gas". Although you could carry two different nitrox mixes and switch to each at the optimal depth, you'd normally only carry one. Typically that's 50% oxygen, though I sometimes use 80% and I have used 36%. Depends on the circumstances and how long the deco will be. Calculating your gas consumption for each gas you're carrying, and if you're diving with a buddy doing the same for each of you and combining the results to see how much gas you should be carrying to complete your dive safely, is one of the principal skills learned in courses such as IANTD Advanced Nitrox. A course I can't recommend too strongly for any serious diver.

yes, i know. i make dives to these depths.

just always found it interesting when people refer to "deep air"

i have always just had my tanks filled with Nitrox21

seems to work well no matter what depth i've used it at

never had any problems with it, still remember the dives afterwards

[drdiver]

QUOTE (drdiver @ Oct 5 2005, 08:30 PM)
Reliable, relatively inexpensive CO detectors for tanks can be fitted fairly easily. There's a thread about this on another forum. If someone would like the link, PM me.

I'm very interested, and I suspect quite a few others will be as well. Can you post the info publicly? [/QUOTE]

Sorry, we can't post about other boards even if it's a safety issue.

I've PMed you the link. There's a discussion about how you can build a tank monitor from a home CO detector and the sensitivity is about as good as this commercial unit and save some $$ which is interesting all and in itself.
Here's the link for the commercial CO detector.

Commercial CO Unit

Edited by drdiver, 06 October 2005 - 05:43 AM.