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I found this paper online and thought I should post a link. It's a great read especially if you're thinking of going deep on air:
http://www.oseh.umich.edu/diving%20articles/abolish.pdf
So what's your personal dept limit on air? I just did my deepest dive on air a few days ago down to 141 FSW and felt comfortable and kept well within my no-deco limits on my computer.
190 max depth on air because of Partial Pressure! Time is the major factor, what can you do on a no deco profile below 130ft? Add narcoses and what can most people do at that depth anyway? A single picture and salvage job, hooking a line, maybe? Most people become very non-functional below 160ft. Simple tasks become impossible! So unless you have very good reason to go deep, don't! :eek:
I fully agree, 99% of my dives are in the 60-80ft range or less, and I knew AAUS air limt was 190 but most other orginizations are 130. I was more after personal comfort levels and the only reason I went deep was to follow the shelf down the rocky reef which was our plan. I ended up with a 40 min dive but only 8 mins was under 100 ft.Quote:
Originally Posted by Papa Bear
Done about 150, Blue Hole, Belize. Felt fine, no obvious narcosis, but then again I wasn't actually trying to do anything.
I know some folks who've done a lot deeper, but usually for a specific reason. Some friends did Chuuk last year and they certainly hit 170+ on air, not sure for how long or what the deco situation was.
I'm with you Papa, unless there's a good reason, I'll stay much shallower. Anyway, I'd rather spend an hour on a reef at relatively shallow depths than go deep and only have 5 minutes down there. Also, aside from NDL restrictions, the deeper you go the quicker you use the gas in your tank, whatever it is.
I did the blue hole in Belize too! Very nice. I was at 140+ on air which was deep enough to get to the huge stalactites. Besides there wasn't a lot past there to see. We stayed down 8 minutes I think. I have been to max 170 on air on another dive but for just a very short time..a minute or so. There wasn't much to see there anyway. Unless you're going to get a look at a shark or something else down there of interest it aint really worth going down there. Less to see and you shorten your dive time and your dive com will nag you a lot on the next dives if you don't have one made for deco diving.
Here is video in the Blue Hole to 171ft! Even running a smooth camera at that depth is hard! http://twotankedproductions.com/trav...ressoriii.html
On a closed circuit rebreather with air as the diluent 165 feet which is the deepest I have been is the equivalent to being on air as far as nitrogen loading.
At 171 ft you must have been near that ridge below the stalactites. Is that where you saw the devil ray from? Nice spotting anyway! You really lucked out!
Been to 180 ft by accident. Spearfishing in the Gulf and didn't realize I had gone that deep. Computer said it was time to leave. I really didn't feel any different at that depth....:rolleyes: well at least that is what I thought at the time.:D. Tim
Quite happy at 60m (180') in the UK, 80m (240') abroad in warm waters. But, only if I need to.
I prefer the CCR with an END of around 20m (60') for anything deeper than 40m (120').
240 feet on air? I see you like Russian Roulette! Haha.
This is a huge debate that's been going on for a longe time. How deep on air is really up to you and your training.
There's the ridiculous 100m club in egypt that do it on air with a bounce dive. And then GUE say after 40m you should be on trimix.
I think everyone is different, i've dove to 80m on air before, it was a difficult dive and a working dive too but sometimes it needs to be done. I would never recommend anyone else do that but sometimes dive theory about partial pressure is exactly that.. theory.
I would say for most, in my honest opinion, 55m is the max, any more then that and you get penalized in a huge way for decompression.
I think it's highly individual and dependant on what's happening on the dive. Warm v. cold water, good visibility v. bad visibility, working hard v. not working, problems v. no problems . . .depth is only one factor.
When the fish start talking to you....it's time to go up!:D Tim
You get used to it. I'd say the same about diving deeper than 30m on a single cylinder.Quote:
Originally Posted by Nemo
doubles for anything deeper than 30M huh?? I heard of the "rule" don't go deeper than the cf size of your tank, and even that seems conservative.
I did my deepest dive to date in the Blue Hole ( Dahab) in 1998 I reached 56 meters but to be honest I did not enjoy it at all I was to concerned with the increased risk factor of deep diving to have a good time, I vary really go deeper than 25 meters these days unless there is really something I want to photograph.
Let's face it, trimix only last 8 9 / year has been most popular and availability is still a problem. Diving words, got gas diving is still very much in my childhood and indeed increasing popularity.At at least I'm on a mix in and feel comfortable and aware of their actions.
i have done 56 meters on air in Dahab Egypt, i was young and stupid at the time would i do it again no!
Your childhood? What are you talking about? Your posts make no sense.Quote:
Originally Posted by simesdwin
Stay within the limits! Its hard to imagine how quick things can turn bad
My qualifications state '60m on air', I try to stay within those limits but occaisionally go a little deeper.Quote:
Originally Posted by myscubastory
What agency makes that statement?Quote:
Originally Posted by Okeanos
I think most would be fairly narced at 180 feet on air.....
My TDI Extended Range did when I did it.Quote:
Originally Posted by acelockco
I see they do, doesn't sound like the safest or smartest thing to do in my opinion but then again I can't imagine doing that dive anyway. I imagine you would have to do a bounce dive (hit bottom and start your way back up right away) or have to carry so many cylinders it would be a workout at minimum. With mixed gasses and especially re-breather technology as advanced as it is there are safer and easier options.Quote:
Originally Posted by Okeanos
I think for most diver keeping at recreational depths gives them much more for their diving dollar. Diving reefs and shallow wrecks is within the reaches of just about every diver. The cost of diving deeper in classes and gear would surely add up to more then the cost of an extreme number of dives.
Like I said, for most, and there are always people that want to go beyond that, which is great as it helps improve our knowledge and diving technology.
60m is relatively shallow in the technical world. 30 minutes at 60m would require 2 x 12L (Ali 80) and 2 x 7L (Ali 50'ish). The bottom time difference between air and mixed gasses is negligeable or even equal as is the deco that follows. The mixed gas (Helium in the mix) reduces the narcosis (and helps reduce PPO2 to a safe level) and that's it. Air at 60m is actually a higher PPO2 than recommended but it does reduce your deco :) I am quite happy doing a 50m dive for 25 minutes with a single cylinder (100cuft) on my back and 2 x 3L (1 of air, 1 of oxygen) side slung.Quote:
Originally Posted by acelockco
If you want to trust a rebreather then the weight would be similar to the 2 x 12's. If, like me, you wouldn't trust the rebreather you'd need to take as much gas as if it was open circuit to be able to bail out of the rebreather and finish the dive safely.
Open circuit is the safest for several reason, below 40m most people would add Helium, on a rebreather anyone with any sense would add Helium deeper than 40m. World record is 320m for OC, far deeper deeper than a rebreather. The main advantage of a rebreather is saving Helium, it is an expensive gas and is going to get more expensive every year until we run out in 2015/6.
Max partial pressure for O2 is 1.4 and the contingency is 1.6 - this is but one of the reason why recreational diving doesnt go deeper than 40m
Quote:
Originally Posted by Okeanos
No No No.....Helium Privatization Act of 1996 stipulates that the US National Helium Reserve must all be sold off by 2015. At that point Helium will be available as we have not mined it all, but the prices will go up a HUGE amount as the market will dictate prices again.
PPO2 of 1.4 gives you 56m on air, PPO2 1.6 gives you 66m on air. You stay safe and the within limits you are qualified to and have experience of.Quote:
Originally Posted by myscubastory
So what do you think ppo2 limits have changed since i started diving from 2.0 bar now up to 1.4 bar or less. Ought to they return to NOAA CNS exposure tables??
It's all down to the odds. I read somewhere that with a PPO2 of 1.6, 97% of people show no side affects. Can't remember what it was for a PPO2 of 2.0 but the odds dropped to something like 80%.Quote:
Originally Posted by deneeshbarosa
I've read Oxygen and the Diver several times and have made my own conclusions as to the affects of higher PPO2's.
We learned that the high set point should be no more than 1.3 bars, an the low is .7
Over repetitive dives some guys have had vision issues at high setpoints.
Can't use a set point on OC but you can get out of the water a lot quicker than CCR.Quote:
Originally Posted by The Publisher
Hi set point of 1.3 is to counteract the spike after an O2 inject, most CCR users I know run 1.6 on ascent.
I am always presuming we are talking CCR diving. 1.3 is the standard CCR high setpoint P02 but I am sure there are guys who deviate from that.
At a P02 of 1.6 one is going to be getting constant 02 injection from 20 feet and shallower so we always switch to the low setpoint above 40 or so feet.
1.3 is the standard as set, it can be changed. I lower it for really long dives i.e. >2.5 hours.Quote:
Originally Posted by The Publisher
I leave the set point at 1.3 until I finish my 3m (10ft) stop and manually add O2 to get to 1.6.