Staged multigas diving is not suited to recreational diving. Primarily, it is not necessary and offer very minimal benefit. Nitrox is well suited to rec. dives. Really guys, 2min O2 safety stops, recreational deep stops, recreational 40 ft. gas switches... How about a little realism. Why the complexity? For the sake of "show". Why not no-deco, recreational Trimix... hmmm, hypoxic safety stops or gas switch?
02 on non deco dives
- Thread starter Boomer7
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Years ago the ascent rate was 60/min (with most divers vastly exceeding it), nitrox was a dirty word and helium was even worse. Also, Haldane ruled and safety stops were done briefly at 10 and then they progressed to 15 knowing that deeper was better (anti-Haldane). As this sport has evolved, it has been learned to get the best advantage from safety stops and to reduce a gas load, 15 (while still good and better than nothing) is not deep enough for the deeper dives. If the purpose of a safety stop is to reduce a gas load, why not take the best possible advantage. Divers are now using slower ascents, nitrox and doing safety stops. This would have sounded complicated years ago, but now it is turning into the norm.. There is no reason recreational divers need to be considered inept. They are now expected to do slow ascents and safety stops, so there is no reason they cant do them deeper. As divers continue to learn, there is no reason they cant also make the most of their safety stops and use a gas switch such as 50% to get the best benefit from their stop if they have advanced to that level. There can be a significant difference in gas washout when doing a safety stop an enriched O2 gas. If the bar is lowered, they will perform poorly. If the bar is raised, they will learn and rise to its expectations as they continue to take classes and improve on their diving.
If you are planning on using multiple gasses on a dive, you are doing a decompression dive. Actually, all dives are decompression dives, but you are just using ascent rate and a safety stop to decompress nitrogen.
By using a higher nitrox blend or O2 on the way up, you are excellerating the decompression of the N2. So, don't kid yourself. Either plan it as a deco dive and use the deco tables, or just dive the recreational tables.
There's no voodoo to it. If you felt comfortable with the knowledge from the class, then go put it to practice.
The problem with doing a recreational dive and then using O2 on the safety stop is that you have no idea where you are on the OTU or RN tables. Sure, you're more conservative, but where? Planning it as such gives you the knowledge of what's actually going on with your body.
By using a higher nitrox blend or O2 on the way up, you are excellerating the decompression of the N2. So, don't kid yourself. Either plan it as a deco dive and use the deco tables, or just dive the recreational tables.
There's no voodoo to it. If you felt comfortable with the knowledge from the class, then go put it to practice.
The problem with doing a recreational dive and then using O2 on the safety stop is that you have no idea where you are on the OTU or RN tables. Sure, you're more conservative, but where? Planning it as such gives you the knowledge of what's actually going on with your body.
MonkSeal
Contributor
mempilot:
CNS clock is more to concern then OTU.
I'm sorry, we seem to be bluring the boundary between tech diving and recreation, again. Applying technical diving proceedures to recreational dives is NOT smart. Simplicity is. That's what prevents problems and complications and accidents, its what establishes safety. You are failing to recognize the diminishinig returs here. Why go to the trouble, effort, calculations, RISK and cost of multi gas diving and apply it to recreational scenario's, limits and depths. You attempt to re-inforce or justify the choice by cutting custom tables and realize a perceived gain. Doing so (on repetitive dives especially) will likely "bend" or fault your computer and actually eliminate the true benefit of the multilevel dive computer OR you will actually shorten your bottom time and/or prolong your ascent time because you are trying to follow your tables and not getting the benefit of the computer's multilevel ability. All that and you give up the enjoyment of an "easy" dive. O2 and gas switches get you out of the water in a reasonable time - FOR DECO DIVES. If you want to add a safety factor make a 4 minute safety stop or dive a smart profile. Anything else and you're just playing games.
How do deep safety stops or a gas switch bend a computer and eliminate its multilevel capacity?msandler:
mempilot:
Folks,
With all due respect to my fellow pilot, since he has hit the nail on the head, I will hijack (---a bad word in our business---) his comment and re-state it.
It is important to remember this fact:
ALL DIVES, WITHOUT EXCEPTION, ARE DECOMPRESSION DIVES. ON THOSE DIVES WE DESCRIBE AS "NO DECO", THE DECOMPRESSION IS TAKEN CARE OF BY LIMITING OUR BOTTOM TIME (I.E. INERT GAS DOSAGE), AND ASCENT RATE/SAFETY STOPS (OFF-GASSING).
I put this in caps because this basic fact is often missed in discussions of this part of diving. It is, however, an essential foundation of any discussion of the issue.
In our usage, "decompression diving" merely means that we intend to stay at depth for a time period which will load our systems with inert gas to the point where we will have to hold at various points for a time period to allow the gas to come out of solution and be dissipated by our bodies at a RATE that will not be harmful to us, i.e. not put us into (as Dick Rutkowski famously put it) "Bubble Trouble".
Cheers! :book3:
Blurring the boundary between rec and tec with deep stops and a deco mix? You say that like it's a bad thing.
If someone is advanced nitrox trained (or even just plain nitrox trained and using Nitrox 36 or Nitrox 40) what is the big concern with using a hotter mix for ascent and saftey stops to add a bit more of a saftey margin a traditional table or a multilevel computer dive?
I often do couple technical deep deco dives starting very early in the morning with my technically inclinced buddies and then do a couple shallower non deco recreational dives in the mid-afternoon with my non-technically inclined spouse. It makes a lot of sense to me to do the ascent and saftey stops on the repetetive rec dives with the 50% left over from the moring dives.
Since it really is not all that hard and since no real planning is required other than to continue to dive the air/nitrox table or dive computer like you normally would and just switch to your deco mix for the ascent and a 3-5 minute saftey stop, don't see that it is out of the realm of a rec diver. It is really not any different in concept than diving nitrox while using an air table or air computer to add a saftey margin.
It is also a practice that would encourage the use of a slung deco bottle that with 40% or 50% is also a useful bailout through much of the recreational depth range.
Besides, there is a long history of the boundary between tech and rec diving being blurred. Nitrox started out as a purely technical diving gas and was regarded as some sort of devils brew by the rec community - until the boundary got blurred and then eliminated completely. Now we have recreational trimix courses (that I personally think are an incredible waste of He) that are further blurring the boundary.
We also have things like deep stops, RGBM computers and all kinds of things that indicate the rec community is continuing to explore new deco options. This also has a long history. When I was a kid the wisdom of the day was you can't bend yourself on a single dive a day with a steel 72. (It was more or less true if you stayed above 90 ft and believed the US Navy tables.) When I was certified in the early 80's we used the US Navy tables, a few years later we used US Navy tables adjusted to more conservative limits with doppler ultra sound research, then in quick succession we had saftey stops, a whole bunch of new tables, affordable dive computers, Nitrox, Nitrox computers, and now deep stops. So the consideration of a rec diver using a hot nitrox mix for a saftey stop seems part of an entirely normal and predictable progression to me. Tech leads the way and rec follows, what makes you think that is ever going to change. Stop fighting it and just be proud of it.
I also can't see how the wider use and acceptance of a tech technique is going to hurt either the rec or tech community. In the past when this has occurred, everyone has benefitted. Except perhaps the minority of tech divers who live for the oohs and ahhs of the lowly and awe struck rec divers who marvel at the macho tech diver's alien equipment and mystical diving skills. De-mystifing tech diving does tend to put a crimp that sort of ego massage.
If someone is advanced nitrox trained (or even just plain nitrox trained and using Nitrox 36 or Nitrox 40) what is the big concern with using a hotter mix for ascent and saftey stops to add a bit more of a saftey margin a traditional table or a multilevel computer dive?
I often do couple technical deep deco dives starting very early in the morning with my technically inclinced buddies and then do a couple shallower non deco recreational dives in the mid-afternoon with my non-technically inclined spouse. It makes a lot of sense to me to do the ascent and saftey stops on the repetetive rec dives with the 50% left over from the moring dives.
Since it really is not all that hard and since no real planning is required other than to continue to dive the air/nitrox table or dive computer like you normally would and just switch to your deco mix for the ascent and a 3-5 minute saftey stop, don't see that it is out of the realm of a rec diver. It is really not any different in concept than diving nitrox while using an air table or air computer to add a saftey margin.
It is also a practice that would encourage the use of a slung deco bottle that with 40% or 50% is also a useful bailout through much of the recreational depth range.
Besides, there is a long history of the boundary between tech and rec diving being blurred. Nitrox started out as a purely technical diving gas and was regarded as some sort of devils brew by the rec community - until the boundary got blurred and then eliminated completely. Now we have recreational trimix courses (that I personally think are an incredible waste of He) that are further blurring the boundary.
We also have things like deep stops, RGBM computers and all kinds of things that indicate the rec community is continuing to explore new deco options. This also has a long history. When I was a kid the wisdom of the day was you can't bend yourself on a single dive a day with a steel 72. (It was more or less true if you stayed above 90 ft and believed the US Navy tables.) When I was certified in the early 80's we used the US Navy tables, a few years later we used US Navy tables adjusted to more conservative limits with doppler ultra sound research, then in quick succession we had saftey stops, a whole bunch of new tables, affordable dive computers, Nitrox, Nitrox computers, and now deep stops. So the consideration of a rec diver using a hot nitrox mix for a saftey stop seems part of an entirely normal and predictable progression to me. Tech leads the way and rec follows, what makes you think that is ever going to change. Stop fighting it and just be proud of it.
I also can't see how the wider use and acceptance of a tech technique is going to hurt either the rec or tech community. In the past when this has occurred, everyone has benefitted. Except perhaps the minority of tech divers who live for the oohs and ahhs of the lowly and awe struck rec divers who marvel at the macho tech diver's alien equipment and mystical diving skills. De-mystifing tech diving does tend to put a crimp that sort of ego massage.
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