"Reasonable" Deep Air...

[SWFTD]

The issue is prompted by the recent spike in Helium prices. I went for a "normal" dive expected to bottom around 180 feet and so asked for a usual mix of 21/35. Well the price for this (into an empty set of double 120's) was around $240 -- and I highly respect and trust the dive shop and its owner who filled the tanks.

Six months ago I lost my job, although I have started a new one in the past 1 1/2 months. I am ok financially now but need to be cautious. I can afford a boat ticket, deco fills, and 80 or 90 dollars of trimix but not a total of $340 for just the main tanks and boat ticket (plus more for deco bottles) for one dive.

I have always "played by the rules" and never exceeded a PPN2 of 4. I know it used to be the norm for people to dive 200+ on air but I have not. I am not aware of any narced sensations at a PPN2 of 4 and seem able to do the required tasks, such as blowing bags alone, etc., without difficulty.

If I could dive air to 185 it would certainly increase my ability to dive more frequently. I am not asking for any guarantees or definitive answers but I am curious how others who have dove air (recently) to 185-ish (1/3 more PPN2), have to say about it.

Thanks, and I DO take everything I hear with at least a few grains of salt.

 

[Teller]

Ive done dives to 180 on air but prefer not to. My prefer trimix below 150 however I dont think its worth the money to dive trimix shallower then 150. I know many disagree but I think its a waste of helium unless the narcosis at those depths is really effecting you.

 

[wedivebc]

I dive deepish on air on occasion but my buddy and I always have an understanding that if either of us feel the least bit impaired on a given dive we will change our target depth accordingly. I certainly don't feel diving deep air is an accomplishment but I also don't think a jaunt below 130ft on air is cause for concern either, at least for me and those I dive with. YMMV

 

[TSandM]

I have never gone deeper than 130 on air. But I HAVE made three separate and distinct errors in caves at 100 feet on Nitrox, without in any of the cases feeling that I was narced. All three errors were atypical of me, and could have been dangerous. I will not go to 100 feet in a cave without helium now, and I'd be careful about what I did in OW.

 

[japan-diver]

Narcosis is a funny thing - most people who are "narced" do not realize the effects or how much they are actually effected. I would dare say beyond 100ft we are all affected to some degree so therefore the risk level increases. I have and will dive air to about 150ft if the dive is relatively benign- no penetration, easy bailout to ascend, low workload as the dives get more complex the END gets shallower and shallower. For complex dives or penetrations I will keep the END below 100ft. I will also run 21/20 or so for shallower dives to save a bit of money. At 180ft a 21/20 mix will give you an END of about 125fsw which for me is well in my comfort zone for non-penetration dives. Because the effects of narcosis vary so widely between divers and from day to day the final decision on this has to be made by you and your team as to what is the acceptable risk for the dives.

 

[Diver0001]

If I could dive air to 185 it would certainly increase my ability to dive more frequently. I am not asking for any guarantees or definitive answers but I am curious how others who have dove air (recently) to 185-ish (1/3 more PPN2), have to say about it.

Thanks, and I DO take everything I hear with at least a few grains of salt.

I've done quite a few deep air dives in the 185 range over the years and all I can tell you is how it affects me personally. Narcosis being what it is, it's hard to predict how how it will affect anyone else.

In my case I notice two major effects:

1) my concentration is reduced AND thinking is slowed
2) I personally become very relaxed. Perhaps *too* much so considering how deep I am.

I'm confident that I can handle most tasks adequately at that depth but they take longer than normal. That's the effect of narcosis on me. I could pop a blob, assuming I had a long enough spool for it to reach the surface, or any other "normal" activity like monitoring gas supply, time, team contact, communication, navigation etc. No problem.

Where I'm pretty sure I would have a problem would be with high levels of task loading. If someone suffered a major equipment malfunction then it would be hard for me to handle that at the same time as making sure the team stayed cohesive, or to delegate navigation to someone else, refer to backup gas plans and deal with the malfunction at the same time. (don't even ask me to make calculations in my head at that depth. It has to be thought through before the dive and put on a slate) These things would have to be done one at a time, which they normally are anyway, but because it takes longer, it might take *too* long if done at depth, which could cause the task chain to get bunched up. Other complications that I would not even consider at that depth would be things like wreck penetrations or any kind of overhead that would create a navigational complication if something were to happen. Choice of dive site is paramount to keeping complications to a minimum.

Knowing this, I only ever make deep air dives with one other person so there isn't a lot of complication with the team and the contingency plan for most unusual events is to immediately gtfo back up to about 30 metres (100ft) and go from there. Again, choice of site is important to facilitate this! In other words, you need to think through contingency plans ahead of time and everyone needs to be on the same page about how unusual events are handled. The other part of that is that you don't do these kinds of dives with just anyone.

Be aware that I'm talking only about how it works for *me* (and my buddy). The guy I do these dives with is a buddy I've done about 1000 dives with already. I can read him like an open book and he handles narcosis similarly to the way I do. In contrast, most other people make me a little nervous at that depth. My tek instructor, to give one example, is terrible on narcosis and completely loses track of navigation and depth awareness if you take him deep enough. Even though his a much more "qualified" diver than I am, he absolutely *must* do dives deeper than about 35 metres on trimix.

I know these kinds of discussions are taboo and I know I'm putting myself out on a limb by discussing it so I would like to ask people to avoid calling me an idiot. I'm not suggesting anyone do these kinds of dives, just sharing my experience, for what it's worth, with the op.

As a final statement, if you make a lot of dives in this range, then your best strategy for keeping costs down on the long run is probably to get into a rebreather. Literally everyone I know who makes a lot of deep dives uses them at least in part for this reason. Maybe some of the rebreather divers can give you a rough idea of the different in price.

R..

 

[PfcAJ]

The trick to saving $$ on helium is it own 2 sets of doubles. Its a somewhat hefty initial cost (less so if you buy used), but you can switch between nitrox and tx dives without dumping all that helium. When you're never filling from empty, it gets a lot more reasonable.

 

[Kevrumbo]

If you're in warm tropical 28deg C waters, no current, good viz, on an external easy tour of a wreck (like here in Truk Lagoon where I've been for the past two months), you can cognitively accommodate to deep air fairly well at max depth probably no deeper than 45m. You have trained muscle memory to handle most contingencies albeit you may be slower to process, problem solve and react . . .so you strategically mitigate your activities to avoid potential tactical overload in an emergency situation --i.g. don't penetrate the wreck; don't physically exert yourself to CO2 retention levels & starting the vicious dark narc cycle; don't do any extensive computations on-the-fly to your deco schedule; go no deeper than 60m or ppO2 1.47 etc. --keep it all nice, easy and simple. . .

btw, Truk Lagoon Dive Center will mix GUE Standard Trimix Gases only if you have no limits on your credit card

!


Oxygen: $0.03/L or $0.93/cuft
Helium: $0.10/L or $2.95/cuft
Estimated Standard Mix Gas fills for one set of Double AL80's:
21/35 $205
18/45 $260
15/55 $310

 

[chrisch]

The cost issue is a difficult one. One of the effects of narcosis is to reduce the recollection of the dive and the pleasure of the dive. Therefore if you have paid for every part of the dive other than the incremental cost of helium it seems to me you are not really getting the best out of the dive despite the high cost of a typical deep boat dive. Don't forget you have paid all that money for training too!

Personally I would say if you cannot afford the gas then make fewer deep dives and choose a less deep venue.

There are places in the world where helium is not available and it is therefore not an option. The discussion and debate as to how deep you can "push" air for those dives is separate in my mind to this. We all have our own personal level of tolerance and comfort for nitrogen, but for me if I was undertaking a dive that is worth all those boat fees, planning and travel costs I wouldn't scrimp on the gas. I guess really it depends on what is available as an alternative. 185 (60m) is too deep for me on air.

 

[Trace Malinowski]

I agree with Teller, Kevin, and Dave though he didn't specify how deep below 130. 150 feet is certainly reasonable for air diving in warm open water.

In the St. Lawrence River, I love the wreck of the A.E. Vickery because you can easily see the entire wreck in a single dive. It is an 1800's 3-masted wooden schooner that lies with the bow in 60 feet and the stern in 130 feet with the stern hanging off a slope. Below the rudder there are two masts at 140 and 150 feet. It's a very easy dive to descend along the slope down to the deep masts, ascend to make a multi-level dive on the wreck itself, then take advantage of moving along the shoal during deco for 20 - 30 minutes and drifting back to the mooring while flying along the wall. With warm summer water temperatures, an easily understood environment that is brightly lit thanks to broken shells reflecting light off the bottom, and well-practiced team and individual emergency procedures, the 10 minutes I normally spend on the deep masts isn't really worth the logistics or cost of obtaining helium.

Conversely, just a hop, skip and jump away from the Vickery is the wreck of the Roy A. Jodrey. It lies below the USCG station on Wellsley Island. It's a 640 foot long steel-hulled self-unloading freighter that sits in 240 feet of water covered in blackish zebra mussels. The descent is a mostly vertical drop which means on air you'll be dropping fairly rapidly which is believed to induce greater narcosis. The top of the wreck lies in 130 feet of water at a mast above the bridge. You need to plan a 170 or 180 foot dive to really see anything. To actually feel like you can explore the superstructure you're looking at a 200 - 220 foot dive. The wreck lies at a deceptively funky angle into the wall easily drawing you deeper if you are eyeballing any structures rather than relying on your gauge. It's dark and eerie looking most of the time. The current is normally ripping on the port side and it's like being on the Death Star due to its enormity. I have days when I really like diving the Jodrey and other days when it just gives me a bad feeling. I think it's a deceptive wreck that probably is a "big dive" disguised as a "piece of cake." You dive after striding off a boat into shallow water. So, it's really a shore dive if not for the fact you can't access USCG property without a boat. After doing safety checks while standing in waist-deep water, you follow a cut down the wall to ski-jump over to the mast. There is no way I would even do a touch dive at the top of the mast at 130 on air on the thing due to the environment not being easily processed as to direction, depth, location of everything, the need to be aware of wires and wreckage above your head, and possible line entanglement from tech divers leaving lines in the water to lead them from the wall to the wreck.

In cave diving, I believe 130 feet is the max for air when the environment is easily processed such as a simple down and up tube like Vortex Spring. I think Nitrox is a better gas for cave diving down to 100 feet and Tri-Ox is better beyond 100 feet.