Redundant Gas - thinking through my options

[markbuk]

Yes your thinking is very correct. But it is more of you MUST have a redundant gas supply when your in an overhead environment or have mandatory deco obligations.

Remember if your on a single tank and you run out of gas or have some type of equipment malfunction your SOL.

My suggestion is to take the correct training for diving like this. ANDP is a good starting point. You will learn about various redundant gas systems and how to use them, how manage them, and how to plan a dive with them.

It is just as important to know how to manage and plan a dive with multiple gas systems as it is to carry them.

I think my original post may have been slightly clumsily worded - I am fully aware I can't do this kind of diving without redundant gas, and am trying to work out what the right solution would be for me.

Whichever route I go for, I'll get training in how to use it. I'm just trying to get a sense of what the pros and cons are of each option (eg I think ANPD is probably too 'technical' for me - I'm unlikely to want different deco gasses as I don't intend to get into more than 5 minutes of deco).

Thanks for all the helpful advice so far!

 

[tursiops]

Semantics can be a fancy term to mean that people do not agree on the meaning of words.

In my world...
A "pony" is a (usually small) cylinder carried for redundancy. It is not part of the gas plan for the dive. I might be slung, attached to your main cylinder, or even side-mounted. Its contents are usually the same as your ack gas, or even just air if you r diving Nitrox. The perfeact dive does not use it. The perfect dive trips means it is still full at the end of the trip.

A "stage" is part of your gas plan, and is usually slung, because it might be staged along your dive route so you do not have to carry it the entire time. This works well for caves, might work for wrecks, and doesn't work at all if you are just wandering about on the bottom because you might not come back to where it is. It usually contains the same gas that you have in your back gas.

A "deco bottle" contains a higher-O2 mix to accelerate your deco. 50%, 80%, and 100% O2 are popular. It is definitely part of your dive plan for gas usage. It is usually slung, and could be smallish or large....depends on your deco needs.

NOTE that only the pony is not part of your gas plan. It is truly redundant...and used only in the case of lost gas from your back cylinder.

You might carry a stage and a deco bottle...they are for different purposes.

 

[johndiver999]

I'm not planning to go into long deco (and hence, probably not planning on doing ANDP either as the AN aspect of it is unnecessary for the diving I want to do - though I am prepared to be talked round on this).

I'm just aware that on some of the dives I do I am limited by my NDL, whereas if I had a redundant source this would be less of an issue - I'm only talking of a very few minutes of deco, which quite often I would expect to clear during my ascent and/or be no longer than my current safety stops, I'm just aware that a gas failure with a deco obligation would be less than ideal. I guess a pony is the easiest option for me to bolt onto my current kit configuration, so it's useful to hear arguments like this as to why maybe it's not the right option!

I personally am comfortable going a few minutes past the no deco line, with a single tank and a pony bottle. Also if you are diving 50 meters, even a no deco dive, you should have some redundancy - in my opinion.

You gotta feel reasonably confident the pony is big enough to get you to the surface in one piece however. To do that, you should probably do some calculations (which incorporate several important assumptions) to see how much gas you need to surface.

Lastly, I get the sense that you may not have a good working knowledge of decompression and dive time relationships. On one hand you say you want to extend your dive time, but on the other you say you want 2-3 minutes (I guess) deco.

Going past the nodeco limit at say 50 m, is going to be racking up deco FAST. In fact staying 20 seconds extra, might earn you 3 min of deco. So it sounds like your goals, or problem statement are mutually exclusive. Going past the deco limit might give you a minute or two or three at depth (depending on dive depth), but that it is it. If you want to meaningfully extend your dive time deep, you need to plan for decompression of some significant amount.

 

[GF99/99]

5min or 5hr of mandatory deco obligation is still technical diving (don't forget your insurance will see it this way a well). When you are in an overhead environment or have mandatory deco obligations it is now technical diving. Its not a big deal but it is just different equipment and different training to prepare your for that type of diving.

When you are in an overhead environment or have mandatory deco obligations you can no longer just bolt for the surface when you have an emergency.

Also I don't think ANDP is "too technical" it is actually one of the best course you can take to make you a better diver. Plus then you would not be learning about redundant gas system and how to dive them from the internet. I am not saying that this board is wrong but also remember this is the internet is that really where you want to learn how to do overhead or deco dives from.

As I said before get the correct training. There is a reason why a thing called NDL exist and there is a reason why an ANDP course exist for those that want to learn how to go past there NDL safely.

Yeah you can learn how to do deco and overhead dives on the internet with out the proper training, yeah chance you would be fine but why risk it.

 

[GF99/99]

If I am not mistaken the number is upwards of 200 deaths now.

Most are single tank divers, diver without the proper training or equipment, or diving beyond there training. And a lot of them are very experienced divers or recreational instructors. Most just doing "light deco"



Link A while back I posted a picture of a friends 1st stage that completely blew apart on the high pressure side. I was with him, this happened around 115m on assent from 140m and we still had around 3-4hr of deco to go. No, issues as we had redundant gas and planned for loss of gas scenarios. But it shows you accidents do happen including catastrophic equipment failures.

 

[markbuk]

I'm not suggesting I want to go to 50m and rack up a long deco obligation, but at 30m on a 15L cylinder quite often it's my NDL rather than gas consumption that limits my dive time. My qualification allows me to go to 50m (extended progressively from 35m in 5m increments), but I haven't been that deep and to be honest don't really intend to. But I'd like to get more out of the diving I do in the 30-40m range (predominantly towards the 30m end of the spectrum).

I know from watching my Surfacing GF at the point where I start to shallow up (to stay out of deco) and tracking it as I ascend that actually if I incurred a small-ish deco obligation at 30m that it would likely be cleared by the time I get to 6m and/or would be no greater than the length of the safety stop that I do anyway, but I studiously avoid going into deco because I don't currently dive with a redundant gas supply.

BSAC training includes decompression (and includes training dives of simulated decompression), so I'm not trying to learn how to do it from the internet and doing deco is technically within the limits of my current training. I can plan dives with and without deco using tables or an algorithm. Equally whatever kit configuration I do go for I'll get specific training in (and the related gas planning) before actually using it. I'm not trying to do serious wreck penetration, but I am very aware that even a swim through (which is the level of wreck penetration I am thinking of) is technically no clear surface so should have some redundancy.

I'm genuinely not trying to learn how to do deco from the internet, I'm after opinions from people who currently carry redundant gas supplies about the pros and cons of different methods. Sidemount for example I'd completely forgotten about as an option, and while I know a pony cylinder is the easiest and cheapest thing for me to add, it's useful to have it confirmed that it's unlikely to be sufficient (I already knew this really, as I alluded to in my original post).

From the advice so far (thanks to all who have contributed), I think sidemount of twinset is probably going to be my best bet... and yes I will absolutely get training before using them in the wild.

 

[formernuke]

I'm not planning to go into long deco (and hence, probably not planning on doing ANDP either as the AN aspect of it is unnecessary for the diving I want to do - though I am prepared to be talked round on this).

I'm just aware that on some of the dives I do I am limited by my NDL, whereas if I had a redundant source this would be less of an issue - I'm only talking of a very few minutes of deco, which quite often I would expect to clear during my ascent and/or be no longer than my current safety stops, I'm just aware that a gas failure with a deco obligation would be less than ideal. I guess a pony is the easiest option for me to bolt onto my current kit configuration, so it's useful to hear arguments like this as to why maybe it's not the right option!

There is so much wrong with this.

If you plan on any deco you need proper deco training.

 

[SlugLife]

A "pony" is ...
A "stage" is...
A "deco bottle" ...

Those definitions seem quite reasonable and common.

You gotta feel reasonably confident the pony is big enough to get you to the surface in one piece however. To do that, you should probably do some calculations (which incorporate several important assumptions) to see how much gas you need to surface.

I also advocate testing those assumptions and calculations. For example, surface from ???-meters, using your ??-cu bottle, and see how much air remains. Even add in some swimming/exercise to simulate a higher breathing rate.

I studiously avoid going into deco because I don't currently dive with a redundant gas supply.

[Part 1]

Personally, I carry a redundant and independent air supply even on 30ft (10-meter) dives. I understand some people can or have CESA from depth, but it's not a gamble I want to take. I treat my redundant supply as a sort of "health insurance" or "PTSD insurance." Effectively, no matter what goes wrong (whether it's entanglements, regulator problems, lost fin, OOA because I'm a dummy, and so on ....), I always have proper gas planned in my primary, and a bonus completely independent air supply sufficient to safely surface.

I understand far less than half of divers do carry a redundant air supply, but what if you need air and you've lost visibility or your buddy swam away? Your profile says "instructor," would you be confident with your students sharing gas with you. What if a student is hyper-ventilating, do you have more than enough for the both of you?

[Part 2]

I'm far from the most strict diver you'll meet, I "self taught" sidemount after-all (don't recommend, hah), but I get a strong sense you're attempting full-on technical-diving while avoiding tech-diving classes.

I'm not a technical diver, but most of the diving you describe is right on the gray-line between recreation and technical diving, perhaps occasionally finning over that line. You're also asking a lot of questions which are probably answered in most standard technical-diving training. It depends on who is offering the course, but technical diving is often broken down into levels.

If you take "tech 1" (or equivalent), but try to stay out of deco that's fine, it's better to be a little over-prepared, than borderline unprepared. Even if I've taken "Advanced open water" or "nitrox" that doesn't mean I have to dive to 40-meters all the time, at night, with nitrox every dive ... it's just an option I have.

 

[happy-diver]

Thanks in advance for any advice you have for me.

Mate run, get out while you still can and do it quickly before the grim reaper really gets your number
and do not bother listening to all those that post what they think others think they should be posting

as a general configuration sidemount in the ocean from boats is for pillocks

 

[happy-diver]

Yeah well my (forced upon me when I want to dive by myself with a chartered boat) scuba bottle
sure as heck works, when I feel like breathing some 50% for whatever reason, whenever I choose

Here I've got a 12l steel with a 2L steel with 50% adorned with double hose and horse collar bcd

Something to think about, do you have any other ideas

A single cilinder with bottomgas + a pony bottle with decogas is not redundant gas.