Deepest safe depth on air?

[Doc Intrepid]

I've been told that you can get used to it, but my thoughts are why even risk it? I'm ok at 100' and so that's the deepest I want to go on air. Later on I may do some tech classes to use other mixes, but for air I'm setting the limit at which I will go. ... I now know that once you start getting narc'd it can snowball on you getting worse quickly with only a few more feet.

...Safe is safe only if you are in total control of the event, and if you're narc'd you are starting to lose control. Losing control is one way to die.

Sounds like you reached a very wise conclusion, Matthew. Good post.

The ocean is a pretty big place. Any perception that we're 'in control' in it is likely an illusion. Still, its possible to give ourselves a better chance of survival, and setting depth limits is one good option. Anyone routinely going deeper than 100' or so could likely find a much better gas than air to take with them.

 

[String]

..if they win the lottery in some places.

 

[DivingCRNA]

One thing to definatetly think about is that my dive to 135 feet through the Devil's Throat and into the Cathedral Room at Punta Sur with 150 foot vis and 79 degree water was a completely different dive from my New Year's Day dive to 90 feet in Blue Water Lake with 5-10 foot vis and 49 degree water.

I felt narced for the first time ever on New Year's Day. Not overwhelmingly, but things took more concentration and I felt the buzz. It has me shopping for a used drysuit so I do not go that deep, that cold anymore. I was never scared or felt in any danger on New Year's, but it gave a good lesson in deep/warm/clear vs less deep/cold/bad vis.

I guess I am echoing others thoughts. Learn you limits slowly and be aware that the total conditions picture is as important as the depth alone.

 

[jeckyll]

....
I guess I am echoing others thoughts. Learn you limits slowly and be aware that the total conditions picture is as important as the depth alone.

... and discuss up front what to do if you start feeling it.

I was recently on a wall dive, where we'd set the max depth to 90' (wall drops very deep). Around 75 fsw I started feeling out of sorts. Nothing was wrong with my gear, my buddies were close, breathing was easy, we were'nt moving too fast or pushing into a current, yet I felt like something was very wrong and couldn't figure out what. Went up above 70 fsw, no problem. Tried 2 more times to get lower, same problem. So I signaled & we stayed above 70 fsw. We'd discussed this potential situation before and had worked out our signals & actions.

I'd never had problems at that depth before, but did that day. I'd slept well, focused on hydration and dove with regular buddies that I was very comfortable diving with and had never expected to have any issues at that depth. But that day I did.

So I guess for me 'safe' is a variable depth from day to day.

Bjorn

 

[JimC]

My limit for air is about 20feet of chlorinated water.

 

[Diver Dennis]

Again thats down to the divers acceptable of risk and what they're willing to accept.

Truk is warm, clear water so generally not as "bad" as a cold deep dark high current narc.

Plus trimix isnt available so you want to do the divers there, air is the only real option.

That brings up another question. Would the folks on the thread here do a 170' dive in tropical waters on air?

 

[WarmWaterDiver]

I would - the thought of a week at Bikini Atoll was what prompted my wife & I to get our beginning Tech diving training & certifications. Our agency (ANDI) also lists 50m (165 feet) but I don't plan to take a shovel and excavate under the keel of anything. Our instructor knew this was our objective during our training. Maybe this year we'll make the trip.

Our tech certification dives all used Nitrox, the lowest O2 mix we used was 25% O2 for 150 fsw dive. We used 50% O2 / 50% N2 for slung decompression mix. Since decompression gases are surface supplied at Bikini this is an extra variable taken out of the task loading and encumbrance.

Our tech certification dives were done off Turtle Reef on Grand Cayman, so conditions at Bikini will be similar. The Bikini diving should actually be easier, as the dives we did at Turtle Reef were all shore dives.

http://www.bikiniatoll.com/divetour4.html

We don't plan on a similar trip to Scapa Floe though, to illustrate String's point.

 

[H2Andy]

That brings up another question. Would the folks on the thread here do a 170' dive in tropical waters on air?

i wouldnt. i'm particularly sensitive to narcosis. even at 120 feet (my
deepest on air) i am noticeably impaired.

but i'm sure most people would be ok.

putting narcosis aside (i.e. assuming it didnt affect me as much as it does)
i wouldn't go past a 1.6 PPO (about 218 feet)

 

[ianr33]

On a slight tangent,does anyone know what the shallowest depth is that an oxygen toxicity "incident" has been known to happen on air? It is my understanding that high partial pressures of nitrogen suppress the toxic affects of oxygen. So you could probably dive below,say 250 on air without much risk of toxing.

This is academic only! My deepest on air is 165. Would probably push it to 170 0r 180 if I was at Truk or Bikini,but otherwise that is enough.

 

[H2Andy]

it'd be really hard to diagnose...

i don't think anyone can positively say that toxicity killed this or that diver, so...

it'd be chalked up to one of those "weird" things that have no explanation
(and, of course, cause of death will be listed as "drowning" :icorolley)