Corregidor
Contributor
..for recreational diving in the tropics (131 ft). I've experienced 60 meters.
DrSteve, is that a typo? 70m = 230ft.
Jim
DrSteve, is that a typo? 70m = 230ft.
Jim
Max. depth on Air
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No...not a typo. BSAC tables cover you to 50m (possibly deeper, I don't have mine at work or I'd check), and I was taught by two different instructors that diving to 70m could be done on air. But it was the absolute limit.
can be and has been done but not smart...... (no I did not do it)
Pete
Pete
Well, I've done about 170 on air. I didn't have too much trouble but my wife turned into a turnip and I had to bring her up. I haven't been that deep without helium since. BTW that was during a class.
Since then I have had less than perfect dives above 140 that I would attribute at least in part to narcosis and I had a student do the turnip act at a mere 120 ft and another at 130ft.
I guess I've sort of become part of the new school that figures that helium is a good thing. i'm ot real strickt about using mix at exactly 100 ft like some are but that's about when I start thinking about it.
Since then I have had less than perfect dives above 140 that I would attribute at least in part to narcosis and I had a student do the turnip act at a mere 120 ft and another at 130ft.
I guess I've sort of become part of the new school that figures that helium is a good thing. i'm ot real strickt about using mix at exactly 100 ft like some are but that's about when I start thinking about it.
The PN2 is theoretically lower at a given depth but I have not seen any research to show that nitrogen narcosis is significantly reduced. There are a lot of other factors involved.
Scuba_Vixen
Guest
All the nitrox courses I can think of teach that Ean has the same narcotic factor as air, because the theory is that oxygen is as narcotic as nitrogen. I've seen some material posted that suggests that O2 is only about 1/3 as narcotic as nitrogen. Empirically, my experience suggests some truth to that. I made some of the same wreck dives recently on nitrox that I have done several times on air. Even though the nitrox dives were much longer BT's than the air dives, I found myself amased at the additional details I saw and how much I had missed seeing on the air dives. Depth was 90' to 100', BT's of about 60 mins, deco on O2. Hope the info is usefull.
Darlene
Darlene
MASS-Diver
Contributor
I'm not really sure what difference exists (between the narcotic effects), it's so hard to tell since it seems narcosis can vary from dive to dive (even at the same depth) for no clear reason. One factor that I have heard mentioned, though, is that O2 is metabolized, while N2 isn't.
You know I am not an expert here but it would seem to me that even if 02 did have this effect the P02 required to cause the effect would have to be MUCH higher then what would cause other problems like O2 toxicity and death. You have to think that with N2 you do not narc until the PN2 reaches >3.0 and in most cases >4.0. If PO2 reached those levels you would have bigger problems but I am guessing convulsions would be cool narced out of your mind J/K.
Pete
My deepest dive was to 212 fsw in 1991 when I had to rescue a diver who got narc'd off his gourd and took off for the bottom on a 5000 foot wall. What I remember most about the incident was the ringing in my ears, the humming in my head and the realization that I was at tremendous risk of doing something stupid myself. I was pretty much at the point of deciding to let him go in deference to my own safety when I finally caught up to him. As it was, we were at the limit of PO2 at that point and even though I new nothing about PO2 at that time, I had no doubt what-so-ever that something was potentially very wrong and the risk level was through the roof.
In answer to the question, I stick to the 130' limit because I teach and, therefore, need to set a good example to my students. For the most part (excluding a few special wrecks perhaps) there's really very little more to be accomplished at 150' than there is at 80' aside from a nice testosterone boost perhaps. Light levels, color, marine life and so on all diminish with depth. There's an inverse relationship between the risk level and the return on the investment in depth. Why dive 200' to see ten fish on a sand bottom with a sporadic soft coral when you can dive 60' and see 1000 fish, expansive coral formations and so on?
The thing that impresses me most about reading this thread is the number of people who are, apparently, mightily confused about what Nitrox is and what it's for... Several even commented about using it for their "deep diving" -- Nitrox is decidedly not a "deep diving" gas. The risks of oxygen toxicity at depth are every bit as great (or greater) as are the risks of narcosis or DCS.
So called "increased safety" from diving Nitrox results from the reduced absortption of Nitrogen resulting from the gas laws. But the absorptions are only reduced if you dive the same bottom times you would otherwise dive on "air" fills. If you are pushing the limits of the EAN tables, then you gain no safety margin. Rather, you gain bottom time. However, you do so at greater risk than you would have diving air because you now must take into account both nitrogen absorption and oxygen toxicity -- two risk factors in place of one. Add deep diving into the mix where nitrogen and/or oxygen narcotic effects are added to the increased risk of oxygen toxicity and nitrogen absorption and the risk level rises even higher.
if you want to dive safer, you dive Nitrox as though you were diving air but you have to both modify your maximum depth limits to shallower depths due to the increased partial pressure of oxygen and you have to carefully track your exposure to O2 unless you are doing shallow diving where the )2 limits far exceed the maximum bottom times a recreational diver will experience in a diving day.
If you want to dive longer, you dive EAN tables but, again, must taking into account the increased risk of O2 poisoning and recognize that your DCI risks and risks of O2 and/or NO2 narcosis remain fixed factors. Diving Nitrox as a bottom time extender increases the risk and requires more skill, experience and good judgement from the diver than does air.
Anyway, that's just my 0.02 -- It just bothered me that so many who know little or nothing about Nitrox were reading so much misleading commentary on it. My hat's off to the few who actually bothered to talk accurately about PO2 risk factors, etc.
In answer to the question, I stick to the 130' limit because I teach and, therefore, need to set a good example to my students. For the most part (excluding a few special wrecks perhaps) there's really very little more to be accomplished at 150' than there is at 80' aside from a nice testosterone boost perhaps. Light levels, color, marine life and so on all diminish with depth. There's an inverse relationship between the risk level and the return on the investment in depth. Why dive 200' to see ten fish on a sand bottom with a sporadic soft coral when you can dive 60' and see 1000 fish, expansive coral formations and so on?
The thing that impresses me most about reading this thread is the number of people who are, apparently, mightily confused about what Nitrox is and what it's for... Several even commented about using it for their "deep diving" -- Nitrox is decidedly not a "deep diving" gas. The risks of oxygen toxicity at depth are every bit as great (or greater) as are the risks of narcosis or DCS.
So called "increased safety" from diving Nitrox results from the reduced absortption of Nitrogen resulting from the gas laws. But the absorptions are only reduced if you dive the same bottom times you would otherwise dive on "air" fills. If you are pushing the limits of the EAN tables, then you gain no safety margin. Rather, you gain bottom time. However, you do so at greater risk than you would have diving air because you now must take into account both nitrogen absorption and oxygen toxicity -- two risk factors in place of one. Add deep diving into the mix where nitrogen and/or oxygen narcotic effects are added to the increased risk of oxygen toxicity and nitrogen absorption and the risk level rises even higher.
if you want to dive safer, you dive Nitrox as though you were diving air but you have to both modify your maximum depth limits to shallower depths due to the increased partial pressure of oxygen and you have to carefully track your exposure to O2 unless you are doing shallow diving where the )2 limits far exceed the maximum bottom times a recreational diver will experience in a diving day.
If you want to dive longer, you dive EAN tables but, again, must taking into account the increased risk of O2 poisoning and recognize that your DCI risks and risks of O2 and/or NO2 narcosis remain fixed factors. Diving Nitrox as a bottom time extender increases the risk and requires more skill, experience and good judgement from the diver than does air.
Anyway, that's just my 0.02 -- It just bothered me that so many who know little or nothing about Nitrox were reading so much misleading commentary on it. My hat's off to the few who actually bothered to talk accurately about PO2 risk factors, etc.
RichLockyer
Guest
You "begin" to narc as soon as PN2>.79
Narcotic is narcotic. Sodium Pentathol is narcotic at levels below 1ata... it would be MORE narcotic at levels above 1ata.
Any narcotic chemical has this characteristic.
1 beer is narcotic
3 beers is narcotic
6 beers is narcotic
Lawmakers have deemed it "okay" to operate a vehicle after 1... but you ARE impaired. Depending on your weight and other conditions, you may be able to get away with 3... but you will be more impaired. You can pretty much figure that 6 is going to land you in jail, and I don't think anyone would argue that you would not be impaired, however, a lot of people think that they can drive safely... many do... or at least, they arrive at their destination.
Just as the person who is drinking, we are our own worst judge of how "narc'd" we are. Equally bad is another diver using the same gas... two drunks don't see each other as being drunk until one is slightly more drunk and falls down... forcing the one who is a little more sober to realize that his buddy is drunk.
The drunk driver can focus on what they are doing and make it home. Leave the bar, turn right, go three blocks, turn left, go two blocks, stop at the stop sign, go one block and turn into the driveway.
As long as that's how the trip home goes, no problem... the guy can make it home well above the legal limit.
Throw in one unusual surprise and everything takes a dump quickly.
Same thing happens diving.
You can focus more intently on a particular task and maybe complete it just as quickly as at the surface, but what about your OOA buddy flashing his light and madly reaching for your reg?
Anyone who claims to be going below 100ft and not getting narc'd is simply not realizing what is happening to them.
Anyone who claims to be going below 150ft and not getting narc'd is guilty of serious denial.
Saying that you don't narc until 120 or 170ft is like saying that you aren't drunk until your BAC is above 0.08 or 0.10.
There's a difference between medical (and actual) "impairment" and the legal definition.
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