Dive tables for accelerated decompression

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diving to 40m without helium in the mix is not necessarily a good idea.

British police search and rescue divers spend extended periods at over 40m using just air, with just a single 12L of air on their back in case the umbilical supply fails. This fact seems to contradict the requirement for helium in the mix or having a large amount of back up gas for decompression.
 
@60plus
you seem to be choosing to ignore some very good advice from very experienced divers - your choice of course

If you think that with your very limited diving experience that you're too advance for Fundies, then I suggest you read the Thread about a fundies course written by @kensuf, who when he took it was already an accomplished full cave instructor

Every diver can learn new things on a course

A tec/deco course will help you towards knowing what you don't know, you don't know. Unfortunately on Tec courses it's not an automatic pass, you can be failed for bad practices or attitude.

The rest of yoru posts just shows how much you have to learn and how far you are from being able to safely make the dives you desire
 
Someone in an earlier post suggested I would be exposing myself to a PO of 2 by using nitrox 32 at 45m.
If you don't see the error in this you should not even be using Nitrox.
If at 45m my air failed I would immediately start my ascent, and in a few kicks would be at a depth where nitrox 32 gave a PO of 1.4 or less.
That would be 34m (I hope you know how to calculate this), but is probably not even necessary. One thing you learn from proper training is that PPO2 (not PO) of 1.4 is not magical, and oxygen toxicity does not occur instantly if you breath PPO2>1.4 or 1.6, and that CO2 buildup is a really bad idea (for both toxicity and narcosis), so kicking hard to get away from 45m is not a good idea.
 
No. Just no. I’m not exactly a fan of GUE, but they will teach you way more in fundies than this. Including why diving to 40m without helium in the mix is not necessarily a good idea.
GUE teach Helium as a standard gas below 30m, Do you do that?

BSAC /CMAS teach Recreational to 50m PADI teach Tec 50 without Helium...

Different people have different reactions at depth, I've never felt euphoric but I do get dark Narced as I approach 50 Others are different and get affected shallower
 
GUE teach Helium as a standard gas below 30m, Do you do that?

BSAC /CMAS teach Recreational to 50m PADI teach Tec 50 without Helium...

Different people have different reactions at depth, I've never felt euphoric but I do get dark Narced as I approach 50 Others are different and get affected shallower
For me personally, it varies. In cold water (Great Lakes) I noticed that I do not remember a whole lot of a dive deeper than 115ft when on air. Even though I felt perfectly coherent durong the dive, and quite confident that I would have handled contingencies ok. But why pay for the boat etc. if I don’t remember much of the dive? Just bragging rights? So I limit myself to about that depth on air, even though my AN/DP ticket is good to 150’. Warm water is a different matter, nitrogen narcosis doesn’t seem to affect me nearly as much.
 
Firstly I never said that diving sea caves without qualifications is safe - it is not. It is however the case that in the instance of that particular cave I was prepared to accept the level of risk that some consider unacceptable.
Regarding decompression diving I also know that you should be trained and build up to it gradually, not just leap off the boat with two tanks and hope for the best.

However my interest in diving is such that I do not want to spend that amount on training or diving equipment. A basic decompression / technical diving course is not that expensive but the equipment is not available at many of the locations I dive.

More generally if people only did what they had learned from others we would still be living in the stone age or possibly not that advanced.

You continue to contradict yourself. Several people have tried to help you and I very nearly did as well. When I initially saw your thread I began posting a link to (free) PDF’s of the IANTD EAN Diving and Decompression Tables, but after reading your responses it became apparent I would only be providing you with the proverbial rope to hang yourself.

According to you “there are two things that limit time at depth, quantity of gas and NDL”. Unfortunately there are many more irritating little details, especially if you “plan” on diving multiple gasses, like EAD, PPO2, FO2, RMV, GF, OTU’s, PATA and CNS, to name a few, all used in conjunction with formulas, tables and gas calculations for comprehensive dive planning. You said you “would become bored hanging about doing deco stops”, so your objective is to do 50m “max bottom time” wreck dives with 50 to 75 minute run times with NO deco obligations. Is this correct? Furthermore, you intend to do a gas switch to AIR after descending to the MOD of your secondary EAN32 stage bottle after entry. How long does it take you to descend 33m to even make a gas switch worthwhile? Do you own a computer with multi-gas switching functionality or does that violate your “minimal cost and minimal complication” criteria? If you are hellbent, emphasis on bent, take @runsongas advice and dive EAN28. Per IANTD EAN28 gives you 10 minutes at 45m with a mandatory 3 minute deco stop at 4.5m. Anything longer than 10 minutes requires multiple extended mandatory deco stops.

I realize my observations are harsh, but I am genuinely concerned for your safety and those around you. For the most part, I have been simply reiterating YOUR words. Seriously, please be safe, prudent and smart. Get properly trained, certified and equipped. Moreover, PLEASE DO NOT PUT OTHERS AT RISK!
 
GUE teach Helium as a standard gas below 30m
I have this weird feeling that (pure) helium as a breathing gas wouldn't be a good idea at any depth.

Trimix, otoh...

BSAC /CMAS teach Recreational to 50m PADI teach Tec 50 without Helium...
My personal flavor of CMAS doesn't recommend diving below 40m without He in the mix. Personally, I'm certified (pun not intended) to 40m and light deco, there's no way I'll go to 40m nor do any kind of deco given my gear config nor my personal skills.
 
Ken, thanks for your positive approach and advice. I am actually away diving in Madeira for 10 days that cover the course dates, however I would not be ready to sign up for a course yet in any case. I have probably already covered the GUE fundamentals course contents as I am qualified to use nitrox and dive to 40m. Post #44. I am not ignorant of decompression procedures and some of the other similar assertions you make are also inaccurate. I talk to other divers and get different responses, this is because what they wish to get out of diving is different. If I was going to do a lot of deep diving the answer would be obvious - get trained and buy the required equipment, but most of my diving is less than 30m with a few dives between 30m and 40m. There are however a few times when I feel I am missing out by not being able to spend a reasonable amount of time in the 40 to 50m range and I am just looking for the most cost effective and acceptably safe way to achieve this. No point enrolling for training only to find that I do not wish to spend the required amount on equipment. Barth post #50 that is exactly the type of information I was looking for when I started this thread - thank you. Someone in an earlier post suggested I would be exposing myself to a PO of 2 by using nitrox 32 at 45m. If at 45m my air failed I would immediately start my ascent, and in a few kicks would be at a depth where nitrox 32 gave a PO of 1.4 or less.
I was really taking the Micky out of Marie13 who got very annoyed at people who suggested she do GUE Fundamentals. Barth’s post is also sort of a Micky take I think. He is not at all suggesting you do that plan. Imagine you get confused over which reg is which and start the dive on the 32%, if you don’t tox your off gassing with be compromised. You also have a problem about what your buddy can breath if they come to you for gas.

If you want to do those depths you ought to have redundant gas. That is not really optional. Accelerated deco is optional. Start with indie 12s, then (with ADP or ANDP) add a pony (ideally >3) of something rich. You will want the pony (although indie 12 here are better) for the 30 to 40 stuff. You probably don’t need to own they cylinders, just the regs, as in places like Scapa you can hire cylinders. This is one extra first stage and and extra contents gauge, so not like a full blown extra twinset, BPW, an Ali 80 and three sets of regs.

The various schemes arrived at by agencies all come back to addressing “what if?”. The training is designed to let you manage those problems and survive, preferably without drama. Some of it is very cheap and accessible. Doing the training doesn’t force you to dive that way but you are likely to learn a few things and get clarifications in person on how you intend to dive. You are much less likely to have whoever is running the training jump down your throat than posters here.
 
British police search and rescue divers spend extended periods at over 40m using just air, with just a single 12L of air on their back in case the umbilical supply fails. This fact seems to contradict the requirement for helium in the mix or having a large amount of back up gas for decompression.

yeah, but they are monitored extremely closely for signs of narcosis - and the 12l is a bailout only should the umbilical get damaged/fail...

you can’t equate what you’re talking about with what they do (and the extensive training they receive!)
 
yeah, but they are monitored extremely closely for signs of narcosis - and the 12l is a bailout only should the umbilical get damaged/fail...

you can’t equate what you’re talking about with what they do (and the extensive training they receive!)

In addition, since there is a support team, should the diver need more deco gas the team can get another bottle to him before his bailout is expended. The S&R diver described is more akin to a commercial diver than a recreational diver.


Bob
 
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