A Case for Spare Air

[2airishuman]

At the risk of getting beat up here, allow me to make a case where Spare Air or equivalent might make sense. And no, I do not own the unit. Below are the very specific conditions I had in mind whereby it sounds reasonable to me. There may be others (e.g., buddy separation, etc.).

1. Solo, therefore it will serve as your redundancy (I know this sounds silly, but see #2)
2. Shallow (< 30' depending on your SAC rate)
3. In the event of an OOA, you will head to the surface immediately

Yes, anybody should be able to perform a CESA from at least some shallow depth, and if you are soloing and can't perform a CESA, well, then, I'm concerned. Anyhow, as for me, I would simply prefer to suck on this on the way up than do the CESA and the capacity seems enough (notwithstanding a few SAC calculations), given #2 and #3.

What say you?

David

David,

I dive solo and have made many dives with redundant air in various configurations. Generally at depths less than 30 feet the surface is my reserve. The capable, reasonably fit diver who has the training, experience, and mindset for solo diving can reach the surface with no drama and no difficulty from these depths.

I don't see any advantages to a Spare Air over a larger pony cylinder with a standard valve with a detachable regulator. Spare Airs are difficult to service and do not provide a way forward when you are ready for a dive that calls for a larger reserve. They do not breathe especially well. They are no less expensive than individual components. They are not materially easier to pack or carry. And due to the lack of a BC connection, you can't use them to inflate the tires on your divemobile.

 

[2airishuman]

I agree with everything here except the deployment time vs. getting up from 30'. These are always turned on, and with the right placement, it should be as quickly as you can grab off your chest and insert into your mouth.

What if you have a freeflow? How will you know it is still full if you've been leaving the valve open -- they don't have SPGs?

I carry my pony cylinder slung and with the valve off. The cylinder and its gas supply are secure and accessible when needed. (Also, it has an SPG.) How long to deploy? I don't know, 10 seconds or something, sitll less time than it takes to make a lazy ascent to the surface from 30'.

Eh, it's more than a couple, from shallow depths that is. I believe the 3 cu. ft. is 50 breaths or so on the surface, depending on your SAC.

Most ScubaBoard pony cylinder discussions, for various reasons, greatly exaggerate the amount of cylinder capacity that is required.

The typical tidal lung volume for a person at rest is usually given as 500 mL. That works out to 57 breaths per cubic foot. (Tidal volume - Wikipedia). 3 cubic feet would be 170 breaths at rest at the surface.

A 3cf spare air provides sufficient gas for a direct 60 fpm ascent (no safety stop) from around 60-80 feet for most divers, assuming that the cylinder is at least 90% full at the start of the ascent, and with no surface reserve or time spent at depth before the ascent begins. That doesn't mean it's suitable for such dives because it is unreasonable to make a contingency plan without allowances for at least some time at depth and some time at the surface.

 

[R.Chisholm]

I really don’t see how buying a spare air makes financial sense – especially in the US.

List price for a spare air 3.0 is ca 289 USD (?) – for a 6 cft tank with a so-so integrated regulator.

In the US you can buy a 19 cft tank with valve for 120 USD or so and a cheap regulator for 175 USD or so (list prices with absolutely minimal searching on the Internet without considering used, or any other bargains)

Admittedly this does not include tank bands and bolt snaps.

You could get the same with a 40 cft tank for little more which should be enough to take you safely from 130 feet to the surface even with a small amount of decompression obligation.

I suppose the 6 Cft/0.45 l spare air is a bit easier on the ever dwindling luggage allowances for air travel.

Other than that I can’t really see the point – if you are likely to run out of air at depths where a 6 cft tank will help you would be better off monitoring your supply and taking some additional training if required.

Alternatively if you are likely to run out of air & are diving at depths where 6cft are not going to get you safely to the surface you probably shouldn’t be diving there in the first place.

 

[Compressor]

At the risk of getting beat up here, allow me to make a case where Spare Air or equivalent might make sense. And no, I do not own the unit. Below are the very specific conditions I had in mind whereby it sounds reasonable to me. There may be others (e.g., buddy separation, etc.).

1. Solo, therefore it will serve as your redundancy (I know this sounds silly, but see #2)
2. Shallow (< 30' depending on your SAC rate)
3. In the event of an OOA, you will head to the surface immediately

Yes, anybody should be able to perform a CESA from at least some shallow depth, and if you are soloing and can't perform a CESA, well, then, I'm concerned. Anyhow, as for me, I would simply prefer to suck on this on the way up than do the CESA and the capacity seems enough (notwithstanding a few SAC calculations), given #2 and #3.

What say you?

David

@certainmisuse If you really believe in this device, please go ahead and use it. No beating up here. What would you do when you go deeper than 30 feet? Would you dive with a buddy and use them in case of an emergency or double tanks or carry a pony? Why learn 2 different scenarios?

 

[certainmisuse]

@certainmisuse If you really believe in this device, please go ahead and use it. No beating up here. What would you do when you go deeper than 30 feet? Would you dive with a buddy and use them in case of an emergency or double tanks or carry a pony? Why learn 2 different scenarios?

It's a fair question, but I only plan on doing shallow diving for a while. I don't want to make this thread about that, however.

 

[markmud]

Why write when I can just cut-n-paste my thoughts!

I carry my pony cylinder slung and with the valve off. The cylinder and its gas supply are secure and accessible when needed. (Also, it has an SPG.) How long to deploy?

Right on!

Most ScubaBoard pony cylinder discussions, for various reasons, greatly exaggerate the amount of cylinder capacity that is required.

Aint that the truth--PFFT! A 40cf for a recreational dive to 60 fsw--nah, I don't think so.

A 3cf spare air provides sufficient gas for a direct 60 fpm ascent (no safety stop) from around 60-80 feet for most divers, assuming that the cylinder is at least 90% full at the start of the ascent, and with no surface reserve or time spent at depth before the ascent begins. That doesn't mean it's suitable for such dives because it is unreasonable to make a contingency plan without allowances for at least some time at depth and some time at the surface.

Yep!

ReefHound, well a large pony anyway; a 13cf or 6cf, or 19cf are OK. They travel well.

Sure, a pony bottle is better but there is theory and there is reality, and the reality is the vast majority of divers aren't going to bother to take a pony bottle when they fly somewhere.

I dived solo with a spare air for years then I came to the conclusion that a 19cf and regulator was not only less expensive but also very easy to throw in a carry-on or checked bag and easy to fill either by the Op I'm diving with or a nearby dive shop and truth be told it's rare that whoever fills it even cares if it's out of VIP.

I love my trans fill whip. I get a shore dive tank when I arrive and my pony is mostly gassed up.

A 13 or 19 cu ft bottle and basic piston reg is more reliable and cheaper if you buy used.

That's what I have. They breathe so nice!

I could make a normal, direct ascent from 90 ft or a little deeper, at twice my average RMV, using a 6 cf Spare Air

Been there done that, quite a few times (practice, not for real, 6cf of gas used. Not a spare air).

That was easy, thanks guys!
m

 

[certainmisuse]

I really don’t see how buying a spare air makes financial sense – especially in the US.

List price for a spare air 3.0 is ca 289 USD (?) – for a 6 cft tank with a so-so integrated regulator.

In the US you can buy a 19 cft tank with valve for 120 USD or so and a cheap regulator for 175 USD or so (list prices with absolutely minimal searching on the Internet without considering used, or any other bargains)

Admittedly this does not include tank bands and bolt snaps.

You could get the same with a 40 cft tank for little more which should be enough to take you safely from 130 feet to the surface even with a small amount of decompression obligation.

I suppose the 6 Cft/0.45 l spare air is a bit easier on the ever dwindling luggage allowances for air travel.

Other than that I can’t really see the point – if you are likely to run out of air at depths where a 6 cft tank will help you would be better off monitoring your supply and taking some additional training if required.

Alternatively if you are likely to run out of air & are diving at depths where 6cft are not going to get you safely to the surface you probably shouldn’t be diving there in the first place.

It's not about the money for me. It's about the smaller size during shore diving transport. Something I should have mentioned. Apologies.

 

[Compressor]

Thank you for your understanding @certainmisuse. IMO over learning a skill is essential in being a safe diver. If you are only going to dive <30 feet and would like to carry it with you on all dives as opposed to doing a CSEA, then go ahead and practice it over and over again until it becomes second nature. If you've every been out of air or close to it, there is not much time to make a decision on a course of action: surface or spare air.

 

[boulderjohn]

Just a historical note that some might find a way to apply here....

I recently saw a PBS show on the history of the SeaLab project, and they started with early research by the Navy that eventually led to SeaLab. They wanted to check out potential procedures for escaping from a submarine, so they took a submarine to 320 feet and had two people do a buoyant ascent from there. (That is a CESA without the C--they had an inflated vest and went up quickly.) They had no trouble exhaling all the way up from 320 feet, going much faster than the standard CESA ascent rate. They were just fine on the surface.

 

[lowviz]

I only plan on doing shallow diving for a while.

Perfect. That shows a sense of restraint. Read @markmud's comments.

It isn't the bitsy little bit of gas you want to carry, it is the false sense of security that comes with it...