29 replies to this topic

[PerroneFord]

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

Well,

I'm happy to know that you have a body that defies the basics of physiology that affect the rest of us. If air works for you, terrific. Your dives will be cheap and easy. For the mere mortals among us, blended gas seems to be a safe option for exploring below 100 or 120ft.

Let us know how that EAN21 works at 250 when you get there...

Edited by PerroneFord, 06 October 2005 - 08:48 AM.

[drdiver]

I'm happy to know that you have a body that defies the basics of physiology that affect the rest of us.

BradfordNC is comfortable with diving at depths greater than 120ft on air. This has been done by a lot of people and done for many years. (I've done it myself) Trimix gives an increased safety margin, reduces narcosis and extends range, but people were doing deep dives for decades on air and doing it with relative safety. There's an interesting discussion of the evolution from air to trimix in the book "Shadow Divers".

[PerroneFord]

Trimix gives an increased safety margin, reduces narcosis and extends range...

...people were doing deep dives for decades on air and doing it with relative safety.

Two HUGE statements...

With the availability of a gas that extends safety, range, and reduces impairment, what is the impetus for using a gas that is inferior in nearly EVERY aspect other than cost? I could drive around in a car with no saftey belts or safety glass either. However, I value my life and try to use things that are considered safe by modern measurements.

People were also DYING from doing deep dives on air as well. What was it, in 1997 when 18 instrutors died using air diving deep? What is "relative safety'? If I dive with only a single second stage is that relatively safe because the modern gear is very reliable? If I dive with a J-Valve but only dive to 60ft is that relatively safe?

To me, this is a simple matter. We have the equipment available to dive to 150ft with no narcosis and that equipment is within the reach of nearly every diver. To purposely dive TODAY (not talking what we did 10-20 years ago) with a gas that we KNOW offeres reduced safety, reduced range, and a much higher chance for narcosis makes no sense at all.

[drdiver]

What is "relative safety'

All safety is relative. Scuba diving is an intrinsically dangerous activity. People die on trimix, too.

[PerroneFord]

Ok, you guys win. I am not He-Man. I'll take the path of "more relative safety" and you guys can dive air to whatever depths you deem safe. 100ft, 200ft, a mile...

[Diverbrian]

What is "relative safety'

All safety is relative. Scuba diving is an intrinsically dangerous activity. People die on trimix, too.

Agreed,

I will preface by saying that I am a firm believer in Trimix. I tend to use it at relatively shallow depths when feasible. But, I am comfortable at a Equivalent Narcosis Depth of 130-150 ft. if that is what my tanks have in them (ie. a "light" tri-mix at 180 ft.).

I thought about it at dinner Saturday night when I heard mention of some of the Grenada dives and the inavailability of mix. What I am doing when I dive to 180 ft. is really no different than 150 ft. on air.

But, I don't recommend this practice for anyone but me and some days not even me. I know the stands of certain organizations and training. I also know that Helium is often unavailable in places like Michigan's Upper Peninsula.

I dive with a couple of divers that dive nothing but air and like their diving to be in the 110-145 ft. range. I'll dive mix right beside them and we are all happy.

And this is coming from a diver typically dives tri-mix or nitrox and very seldom touches good 'ol Nitrox 21. But, I won't critisize those who dive it. People have died on all of the above. Then again, people have died sleeping in their beds too!

[PerroneFord]

Yes, I'm sorry. To each his own.

[peterbj7]

Diving mix can be very dangerous to someone without the proper training and in-water skills. That's why reputable agencies have demanding prerequisites for their trimix courses.

As to deep air, I think the deepest I've dived routinely on air is about 250'. I've even done multiple long dives like that - four dives to 250', followed by three shallower ones, each day for several days. Not proud or ashamed, but I wouldn't recommend it to anyone else, nor am I likely to do it again. At that level it's becoming serious Russian roulette.

[PerroneFord]

Diving mix can be very dangerous to someone without the proper training and in-water skills.

Peter, could you highlight some of the dangers involved in diving mix at 100-130ft? Since I am not a trimix diver, I am very curious.

[Diverbrian]

I hope that Peter shows up soon, but I will start.

Helium goes into the system and saturates much faster than nitrogen. It also comes out much faster. If you are uncertain of your buoyancy control and don't maintain the appropriate stops on the way back up, those bubbles will come up quicker as well. A decompression sickness hit with neurological involvement (which helium hits tend to be) is not a fun thought.

Also, helium is a gas with a high thermal conductivity. This means that it "breathes cold". It can lead to problems as being cold can increase the odds of DCS. You will need a bottle to inflate your drysuit.

Oh, your RMV (or SAC if you choose to use that measure) will likely be higher with helium mixes as they are less dense. You will likely need more gas to do the same dive.

Helium analyzers are available, but they are over twice the cost of an O2 analyzer. Unless you are mixing your own gas so that you KNOW how much helium that you put into the tank (my current situation) or own a helium analyzer (my situation at bonus time next year), you won't be very certain of how much helium is in that mix. This could be bad for the reasons that I mention about the differences in the way helium is absorbed into the bloodstream vice nitrogen.

The deco tables for diving helium mixes are basically a bigger crapshoot than the more traditional EANx/air tables and that increases your odds for a DCS hit even you do most everything right, but are overtired/dehydrated/etc.

I desperately hope that one of other tech divers will elaborate on this, but the bottom line is that much like nitrox, all that you are really doing with helium is trading away one set of risks (reducing those risks involving nitrogen narcosis) for other risks involving DCS. Then you pick your helium level for the risk that you are comfortable with. Nitrox is the same. You reduce the risk of DCS, but increase the risk of Central Nervous System toxicity.

All that these different gas blends are is really a balance beam for different risks. You need the training to decide what risk that you consider acceptable and learn how to best manage those risks by smart and competent diving.

[casematic]

All that these different gas blends are is really a balance beam for different risks.  You need the training to decide what risk that you consider acceptable and learn how to best manage those risks by smart and competent diving.

I know that Perrone has been asking quite a few of the questions on this thread, but reading it is proving to be very educational for me ... Quite a few things I didn't realize about Helium... I'm not really into deep dives so hadn't really explored tri-mixes ... I've been to about 165 (on air)... but I start to feel a little narcosis at about 150 so I'm not real comfortable going much deeper than that .. I've got lots of buddies that have been over 200 on air though (seems that I recall that about 230' is where oxygen toxicity becomes a real danger on air - anybody more versed in deep and tech diving may want to elaborate or correct me on that).

I dive nitrox whenever possible (and I use 1.6 to establish my m.o.d. - I figure that with 2 partial pressures being the point where oxygen toxicity becomes a real risk, that it still leaves a comfortable safety margin)... I don't usually need to go much deeper than 110... If there is a wreck or something I want to see that is down at 130-150 or so then I use air....

The other thing I do when diving is take extra care to keep myself hydrated... I drink tons of gatorade (should drink more water than I do - and that I will remedy), and very limited alcohol (maybe a little more after the last day of diving) .. I've read that dehydration can be a big contributing factor to DCS.

I think it has been said by many on this forum in one way or another that each person has to dive within their own comfort level and in a manner they consider safe....

Thanks for the wealth of shared information. I'm looking forward to meeting and diving with folks on future trips.

[PerroneFord]

I ask a lot of questions by nature, as I think it is an excellent way to learn. Or at least to solicit opinions from a variety of people with different experience levels. Sometimes those opinions jibe, sometimes they don't. Sometimes people get quite heated in their support for their feelings and that is the nature of the game.

Casematic mentioned using pp02 at 1.6 as his MOD which is frowned upon by some agencies who use 1.4 for working MOD and 1.6 for deco MOD. He feels safe with his choices and that's what he does.

There were also strong opinions of taking air to deep levels. As diverbrian pointed out, the use of helium is not without it's dangers as it enters and leaves the bloodstream quickly, offgassing it requires good control of buoyancy so as not to throw off the deco procedures. From what I understand, the same can be said for Deco on pure oxygen versus 80/20. If you can't keep from bouncing at your 20ft stop, perhaps it is best to deco on 80/20 instead. Of course some agencies shun 80/20 and prefer you increase your skills as a diver rather than use an "inferior" deco gas. Arguments can be made both ways I presume.

I suppose as a new diver who hopes to face all these issues as I delve more into the sport, I am forming some conclusions about methodology, certifying agencies, and even potential diving partners. Assessing what people see as reasonable risk, what people prefer to see and do under the water, etc. Clearly there are some divers here who MUCH prefer to stay shallow, some who dive deep, some who take more risk than I feel comfortable with and others who are conservative by my thinking. Variety is a good thing!

I hope I did not offend by my comments about those who choose to dive deep on air. I suppose it's just one of those things to me that I don't agree with and will probably be adamant about. Other gases have their issues as well as has been pointed out.

Hope everyone has a safe and fun weekend!

[casematic]

I ask a lot of questions by nature, as I think it is an excellent way to learn.

I'm relatively inquisitive myself.... and getting the opinions of others is a great way to learn. We can sort through that information and decide what to keep and what to toss...

Its great to be able to tap into the wealth of experience and knowledge that some of the posters on the board have (and are willing to share). Hats off Peronne... Have fun with the classes and someday I'll see you on a trip.

ps (I think that PADI uses the 1.4 and NAUI teachs 1.6 - not positive about that or any of the other agencies though). I'm sure someibne can clarify that.

I think there are lots of factors that affect ones relative safety ... physical fitness.... state of mind.... hydration level... proper rest... dive training... Hey, I'm not telling you anything you don't know...It seems obvious that you take the sport (and inherant dangers) very seriously. Dive safe...have fun.

KC

[Diverbrian]

I ask a lot of questions by nature, as I think it is an excellent way to learn. Or at least to solicit opinions from a variety of people with different experience levels. Sometimes those opinions jibe, sometimes they don't. Sometimes people get quite heated in their support for their feelings and that is the nature of the game.

Casematic mentioned using pp02 at 1.6 as his MOD which is frowned upon by some agencies who use 1.4 for working MOD and 1.6 for deco MOD. He feels safe with his choices and that's what he does.

There were also strong opinions of taking air to deep levels. As diverbrian pointed out, the use of helium is not without it's dangers as it enters and leaves the bloodstream quickly, offgassing it requires good control of buoyancy so as not to throw off the deco procedures. From what I understand, the same can be said for Deco on pure oxygen versus 80/20. If you can't keep from bouncing at your 20ft stop, perhaps it is best to deco on 80/20 instead. Of course some agencies shun 80/20 and prefer you increase your skills as a diver rather than use an "inferior" deco gas. Arguments can be made both ways I presume.

I suppose as a new diver who hopes to face all these issues as I delve more into the sport, I am forming some conclusions about methodology, certifying agencies, and even potential diving partners. Assessing what people see as reasonable risk, what people prefer to see and do under the water, etc. Clearly there are some divers here who MUCH prefer to stay shallow, some who dive deep, some who take more risk than I feel comfortable with and others who are conservative by my thinking. Variety is a good thing!

I hope I did not offend by my comments about those who choose to dive deep on air. I suppose it's just one of those things to me that I don't agree with and will probably be adamant about. Other gases have their issues as well as has been pointed out.

Hope everyone has a safe and fun weekend!

No offense taken. I like to see good conversation that encourages good training to be sought out.

Neither am I "the expert" here. We have many other divers that have been doing this stuff far longer than I have. I just try to make myself aware of the risks of what I am doing and make smart decisions from there.

Have a great weekend yourself.

[peterbj7]

Sorry Perrone, never answered your question. But Brian did very completely. What I had particularly in mind was the risk of an He bend under water, which is about as unpleasant as it gets. Not that I've experienced it yet. I learned the hard way what a good heat conductor helium is - I forgot some of my gear on a tech dive trip and had no choice but to use back gas to inflate my drysuit. My, was it cold! But still marginally preferable to the squeeze I would have had if I hadn't inflated it at all.

Brian said what your experience should have taught you by the time you move to mix - essentially, accurate diving. The ability to hold a stop at an accurate depth and for an accurate time. But you'll see once you get to that stage that the whole area is quite controversial - there are countless theories of decompression and different dive styles that result, and many of them will be presented as THE answer, all others being WRONG. In particular, some people think you should travel rapidly between stops, while others say travel should be slow. The point being that all the time you are breathing mix you may be absorbing helium.

The subject is way too complicated to cover here, but you'll find it fascinating when you get to it. Just don't accept unquestioningly anything that's told to you. Though from your posts here I don't think you're a person to do that!