Going deeper, safely

[gsk3]

Good job taking a thoughtful look at what the requirements to move beyond recreational depths are, before you leaped. If all of the recent deep air quagmire has produced this result--more questions -- then it will have been worth it.

First, a question for you: without decompression, how much time can you spend at 165 feet before you reach your NDL. Once you have that number, weigh that against the risks of doing such a dive without training, and make your own decision as to whether or not it is worth it to you.

A second question: how quickly can you deplete a single AL80 at 6 atm (165ft)? How much gas do you need to hold in reserve to get you and your buddy to the surface if there is a problem. Be sure to take into account that your breathing rate will be markedly elevated under stress, and that it will take a few minutes to sort out a problem and share air. And that those few minutes will add to your decompression obligation.

And we have assumed that the gas switch (perhaps the number one killer of technical divers) goes ok, without training.

Now imagine how much more fun the situation would be with a few martinis in you, and weigh that against about $30 of helium.

Personally when I went through those factors, I decided to get trimix trained. To me, the benefit of an extremely short dive, made stressful by not knowing whether I would be ok if even a single problem cropped up, made the training seem cheap. And I am not rolling in money by any stretch of the imagination (grad student).

32% is not a particularly good decompression gas. You are correct that the more oxygen the better, but it is also true that the more oxygen the more potential complications. So there's a balance which guides gas choice which is not really appropriate for this forum in the kind of detail you'd need to make that choice.

In short, by the tme you get the proper equipment (a few thousand typically), the training is cheap by comparison (in these parts, around a grand for AN/DP, a little more for mix training--these prices are for the better people around).

For now, I'd recommend GUE Fundamentals, UTD Essentials, or a carefully-selected instructor for Intro to Tech (get recommendations here first, and make sure they have really good skills, have clean diving style, good buoyancy and trim, etc.). That will give you a solid foundation on the in-water skills you need to build on for tech classes.

 

[TSandM]

Jonah, you're thinking, and that's a good thing. Let's look at the difference between your original post, and the dives we've been yelping at. You are talking about taking multiple tanks with you -- that's gas supply, and that's one of the things that wasn't planned properly for the dives that killed people. HOW you configure that gas supply can vary, but that you have enough of it, and can access all of it, and deal with any problems the configuration you are using can throw at you -- those things are important.

You're thinking about decompression. That means you have recognized that it takes very little time at these depths to incur enough of an obligation that you simply cannot surface without expecting to be injured. In those circumstances, you have to be able to solve any problems which occur RIGHT WHERE YOU ARE, because you can't go to the surface to deal with them. This ties in with both breathing gas and decompression, because if you run out of gas, you can be forced to surface when you know you will suffer for having done so.

The essence, the real core of "technical diving" (which is often defined as any diving that precludes a direct ascent to the surface), is planning. Especially for big dives, the time and effort spent planning, setting up equipment, arranging backup and emergency support, and the like, will FAR exceed the amount of time spent on the dive (deco included!) And this is not even considering the training that the divers undergo, to make sure they are very solid in their skills, and can remain calm and focused to solve problems when they occur (while still maintaining a deco schedule and staying on the upline!).

An amazing spectrum of dives, many well beyond recreational depths, can be executed with a reasonable expectation of success, if sufficient planning and preparation are put into it. When those things are insufficient, people get hurt.

You seem to be a very curious person -- I would highly recommend two books to you. Mark Powell's Deco for Divers, and Steve Lewis's Six Skills. If you read them, you'll have a much better foundation of information and understanding, as you approach deeper dive. Oh, and for the time being, don't play games with deco . . . risks go up pretty steeply as you begin to do this.

 

[Bombay High]

thanks for sharing your thoughts .... i was actually thinking that ean28-32 would be used for the decompression on the way up since i noticed a while back when i went over my ndl by 2 min that when i was on air(ean21) my suunto added 11 min of safety stop between 6-3m while when doing the same on ean33 i had only 3 min added so i figured that it would be good to do deco stops on higher oxygen mixes..

just to make it clear i am not attempting such a dive but really enjoy thinking about how one would do it safely, as as said above make it back to the surface i recently climbed a peak of 6300m, but had been dreaming, training and planning since more than 3 years....

Eternal Jonah,
Where are you doing these dives ? Who is taking you on these dives ?
You live in Pondicherry and have access to Rob and John. You have no idea where you are headed making dives like this.
Please speak to Rob and take it easy.

Regards
BH

 

[eternaljonah]

just to clarify, i would like the training, love learning. but i live in south india, and there are some divers with tech experience but no courses available here, but i did just order the deco for diver book, thanks for the advice

when i went 2 min into deco on my suunto it was with my buddy still having 12 min on his uwatec and we did start the accent at 0 min left on my comp, but as we went up real slow my computer and me when into deco time.

thanks again for sharing you knowledge

 

[eternaljonah]

Eternal Jonah,
Where are you doing these dives ? Who is taking you on these dives ?

BH

not doing dives deeper than 38m and not planning on going deeper than 40,.nor planning to take multiple mixes or bottles down, just thinking about how one would do it. i am staying within my training and experiance but reading here on sb and being curious by nature. i am wondering as to how one would conduct such a dive..

 

[ajduplessis]

Like they say "The dive went well, then they entered the water"

 

[Colliam7]

I think the difference is due to ...

1. How the question gets asked.
2. The history of similar past discussions with the person doing the asking.

This OP approaches the subject by asking what it takes, rather than making assumptions about what it doesn't need.

OK, I understand. Thanks for the insight.

 

[DCBC]

eternaljonah,

I'd encourage you to join a diving club if one is available in your area. You don't have to take a course to learn, although many people find this easier. Find an experienced mentor with a PhD in common sense (that's better than having numerous certification cards as far as I'm concerned). Go slowly and have fun!

 

[DevonDiver]

not doing dives deeper than 38m and not planning on going deeper than 40,.nor planning to take multiple mixes or bottles down, just thinking about how one would do it.

That's reassuring. However, don't get drawn into thinking that it'd 'still be ok' to push too hard with the 'easy stuff'. Your diving sounds remarkably aggressive - very low (and beyond) NDL. Be aware that you are severely cutting your margin for error - one uncontrolled ascent or a mis-match with your gas planning...and you could get yourself hurt.

As you say, there isn't much technical training because of your location. Does that also mean there isn't much hyperbaric medical support?

Distance to a chamber is a major factor that you should consider if you tend to dive aggressively.

i am staying within my training and experiance but reading here on sb and being curious by nature. i am wondering as to how one would conduct such a dive..

Firstly, your core scuba skills need to be flawless. Technical dives involve a huge amount of task loading, and this will severely degrade core skills unless they are perfected and totally ingrained. For an example, check out the buoyancy, trim and control exhibited in the UTD instructional videos on YouTube, there's lots to look at :

UTD Essentials of Technical Diving DVD - Skills Preview - Gas Switch - YouTube

Secondly, be aware of what situational awareness is. As a technical diver, you need to have second-by-second awareness of your gas state, your depth, time and deco state. You need awareness of your buddy/team and should be able to anticipate everything before it happens. As an example, I get my tech students to record time/depth/gas at strict regular intervals during training dives. It doesn't matter what else is going on (and there is lots!), they have to get that information recorded. I expect to ask a student what their gas/depth/time is at any point during the dive... and get an accurate answer without them having to check their gauges.

Thirdly, technical diving involves far more complex equipment and drills. Screwing up a procedure on a tech dive can kill you very quickly. You need to be very comfortable in the kit and have the procedures ingrain at an unconscious level. Again, the YouTube link above shows the gas-switching drill. It seems simple, but is actually a very formalised process that has to be done right every time. Errors with gas switching have killed lots of technical divers (O2 tox from using the wrong gas at the wrong depth).

Fourth, you need a lot more theoretical knowledge. Others have mentioned Mark Powell's 'Deco for Divers'. That's a great starting point. You really need to understand what is happening in your body when your computer says 'ceiling'. There's loads of decent technical diving manuals and books you can buy to further your knowledge. Some are available as Ebooks for download.

Fifth, you need a high degree of precision and accuracy with your dive planning. And you need effective awareness...and self-discipline... to follow those plans (hence the 'facepalm' funnies earlier, when you described some pretty undisciplined planning/management of your dives). Technical diving isn't about a gung-ho plunge into unknown depths... it's about meticulous preparation and attention to detail. More NASA than James Bond.

You'd need to know your SAC (surface air consumption) to calculate your gas requirements throughout the dive (descent, bottom and ascent at different levels using different gasses). You'd also need to know your accelerated SAC... because you'd plan for contingencies/emergencies - where your respiration rate will be substantially higher.

You'd need to calculate your ideal gas mixtures for descent, bottom and ascent/deco. To do that, you need to have knowledge of decompression theory and also be able to the math to work out EADs, ENDs, PPO2s, MODs etc etc.

The actual dive profile would be produced electronically. This could either be a laptop/pc running dedicated deco planning software (cutting 'custom' tables that you laminate and take on the dive), or you could use your dive computer/s if they could handle the gas types and number of mixes required. Either way, you'd also 'cut' contingency tables - in case you went deeper, stayed longer or both. You'd also work out scenarios for lost gas; especially deco gas. Finally, you'd gas match with your buddy/team... to that you ensure the ability to mutually support. Remember, not every diver has the same SAC... so that has to be accounted for.

Sounds complicated? That's just a very brief overview of technical dives....

 

[mathauck0814]

The actual dive profile would be produced electronically. This could either be a laptop/pc running dedicated deco planning software (cutting 'custom' tables that you laminate and take on the dive), or you could use your dive computer/s if they could handle the gas types and number of mixes required. Either way, you'd also 'cut' contingency tables - in case you went deeper, stayed longer or both. You'd also work out scenarios for lost gas; especially deco gas. Finally, you'd gas match with your buddy/team... to that you ensure the ability to mutually support. Remember, not every diver has the same SAC... so that has to be accounted for.

Decompressing on a computer alone is frighteningly dangerous. Without the tables that DevonDiver mentions you have no plan for when the computer suddenly dies. Now what? I, too, generally dive the schedule that my predator gives me (as it benefits from multi-level and multi-gas diving) but you have to have a back-up timing and depth device and set of tables to interpret that data should your primary (computer) fail.