Do I want a Spare Air

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I am soliciting opinions on carrying a Spate Air secondary air source for emergencies. I am a relatively new diver that is starting to dive down 70 to 90 feet. My primary fear is equipment failure and needing to rely on a buddy. How common are equipment failures at depth? Is the Spare Air a good option for deeper dives?
You are asking good questions, so kudos to you.

The good news - equipment failures at depth are quite uncommon. That does NOT mean they cannot occur. But, if equipment is properly maintained, and good pre-dive procedures (including inspecting the O-ring on a yoke valve cylinder, or on a DIN regulator first stage) are followed, the chances of a catastrophic gas supply failure are very small indeed. Nonetheless, IF they occur, you may not have much time to reach your buddy to get assistance, or reach the surface if that assistance is not readily available. A good article providing actual hard data on the rate of gas loss associated with different equipment failures is available online ((Life Ending Seconds • ADVANCED DIVER MAGAZINE • By Curt Bowen)

As you probably note from the majority of responses in this thread, a Spare Air is not considered to be an adequate 'redundant' gas supply. It is relatively expensive considering what you get, and not particularly functional - 3cf of gas, at depth, is so minimal as to be trivial. Even the newer, larger Spare Air, with 6 cf of gas offers very little. Better than nothing? Yes. Anywhere near adequate as a redundant gas supply when a gas supply emergency occurs at 110 ft? Not at all. When I am diving a drysuit, I carry a 6 cf pony bottle as the gas supply strictly for inflating my drysuit. It really isn't a lot of gas. :(

Carrying a pony bottle of reasonable size (19 cf or larger) is a valid approach to providing a redundant gas supply. Preferences on size, and configuration differ. A 19 cf bottle is small enough to be attached to your primary 'backgas' cylinder, and some people prefer that. I do not like that approach, but that reflects my personal preference as much as anything. I prefer to 'sling' my pony bottle - attached by bolt snaps to a chest strap D-ring and to a waist strap D-ring - because I have better access to the valve, and regulator when it is in front of me. I use 30 or 40 cf bottles, and do not find either to be at all cumbersome or inconvenient, either on the boat, or underwater. The 30 is slightly smaller, and over the years I have gravitated to that size as a (very) slight preference for recreational diving redundancy. For the kind of diving you mention (70-90 feet), either size would work well. I encourage you to make the investment in such a bottle, and a regulator, and the rigging, and learn to use it. After a few dives, you won't know it is there. :) And, you should practice with it, to become 'fluid' in switching to the pony bottle regulator. I started learning to carry and use a 40 cf bottle years ago, on a trip to the Florida Keys. (And, yes, I caught some grief from other people on the boat, including the captain) when I carried a 40 cf pony on a 25 ft reef dive. :) But, that didn't bother me - I wanted to become comfortable diving with a 'slung' bottle. And, I did.

Several posters have specifically mentioned O-ring failures, and that concern merits comment. I have seen a few O-ring failures on cylinder yoke valves, at depth. Usually, they are manifested as aggressive bubbling and do not represent catastrophic failures. They are inconvenient, because the dive usually needs to be called. One alternative, to avoid that possibility, is to switch to DIN cylinder valves and regulators. In the western hemisphere, that is not the norm. But, I have used DIN equipment since I began diving some time ago - my first regulator was DIN - and have never regretted my choice.

I also second scubadada's recommendation to do a search here on SB. There have been a number of discussions on this issue, including some that were somewhat 'animated', and they are worth reading as well.
 
Divers using an AL80, or even an AL 50 which I sometimes use for very shallow jetty dives, would be in no danger of running low on air if they checked their SPG every few minutes. That should be a cardinal rule of diving, giving warning of air consumption higher than anticipated and allowing the diver to adjust their plans to reflect the gas situation. I sometimes carry a small computer, but I rely on my SPG and wrist watch for dives <50 feet. How divers run out of air when they have a functioning SPG is beyond my comprehension. When I was young there were no computers and SPGs were not available. I was acutely conscious of gas usage and limitations, but had only a J valve to rely on. When I got my first SPG sometime in the 70s I thought it was the greatest thing ever invented for scuba. I've never changed my mind. I've never gotten a clear explanation of the reasons for not checking an SPG every 5 minutes or so. Running out of air when an unconsulted SPG has been indicating increasingly limited air remaining qualifies the diver for the Darwin award.

I often try to have it in my head, what I'll see when I next look at my SPG. Usually pretty darn close
 
This completely ignores cold water diving, where free flows are a possibility. It’s common here in the Great Lakes to see single tank divers with Alu 30s or Alum40s tanks sideslung on deeper dives where even in the summer, temperatures below the thermocline can be 40F or 42F. Ice crystals stick the diaphragm open in a cold water free-flow.

Having an attentive buddy donating a working regulator doesn’t mean that your troubles are over. Over breathing the donated regulator while the attentive buddy is also breathing off the other regulator can place too much of a demand on the buddy’s regulators in such cold water. And now you have another free-flowing regulator or two. And two divers in a more stressful situation.

This is where having a side slung Alu30 or 40 is a real peace of mind. You just switch to the redundant tank and end the dive.

Your attentive buddy can assist you in turning off your back tank so it doesn’t continue to annoy with noisy bubbles and deplete the entire tank as you ascend.

Sometimes turning off the tank and waiting a few minutes is enough to stop the cold water free-flow, the ice crystals get a chance to melt, and cautiously turning the back tank valve open means the fee-flow is solved.

But other times the second stage is completely frozen open and the tank gets depleted unless it is shut down. The dive is over.

And while a free-flowing reg is noisy, and obscures your vision with multiple bubbles, in warm water you can breathe around it if you try. In cold water you have a mouthful
of ice crystals.

And for an average OW or AOW cold water diver here in the Great Lakes (or anywhere else with cold water) a side slung Alu 30
or 40 *is* best practice.

SD

Yes...and Yes...

I don't dive with a pony as I find the hooves and tail create far too much interference...

But having said that...I do dive with a fully redundant ''bailout'' system...have done since 2008 during our first trip to NC...where the charter operator...Atlantic Beach Diving...had redundant bailout as a mandatory requirement...

I've slung redundant bailout with singles/doubles/rebreather...my choice...my comfort...my safety...and realizing rebreather...and even doubles are beyond the scope of the OP's original question...

And...I'm not about to change any time soon...no argument/no debate...my choice...

Forget all about how uncommon failures are with modern equipment...if and when...you can't use it...if you don't have it...

Buddy's are good...if they're good buddy's...if like some...they're reliant on you...you may want to be fully self reliant...one of the first things we were taught as children...''be careful...and look after yourself''...

W...
 
This completely ignores cold water diving, where free flows are a possibility. It’s common here in the Great Lakes to see single tank divers with Alu 30s or Alum40s tanks sideslung on deeper dives where even in the summer, temperatures below the thermocline can be 40F or 42F. Ice crystals stick the diaphragm open in a cold water free-flow.

Having an attentive buddy donating a working regulator doesn’t mean that your troubles are over. Over breathing the donated regulator while the attentive buddy is also breathing off the other regulator can place too much of a demand on the buddy’s regulators in such cold water. And now you have another free-flowing regulator or two. And two divers in a more stressful situation.

This is where having a side slung Alu30 or 40 is a real peace of mind. You just switch to the redundant tank and end the dive.

Your attentive buddy can assist you in turning off your back tank so it doesn’t continue to annoy with noisy bubbles and deplete the entire tank as you ascend.

Sometimes turning off the tank and waiting a few minutes is enough to stop the cold water free-flow, the ice crystals get a chance to melt, and cautiously turning the back tank valve open means the fee-flow is solved.

But other times the second stage is completely frozen open and the tank gets depleted unless it is shut down. The dive is over.

And while a free-flowing reg is noisy, and obscures your vision with multiple bubbles, in warm water you can breathe around it if you try. In cold water you have a mouthful
of ice crystals.

And for an average OW or AOW cold water diver here in the Great Lakes (or anywhere else with cold water) a side slung Alu 30
or 40 *is* best practice.

is that relevant to basic scuba diving or is that an exception to the rule? literally no mention of cold water until now. You can find all sorts of ways to justify them, but none have yet to be appropriate to the context of this subforum which is basic scuba diving
 
Considering bringing a spare air to mitigate immediate, catastrophic out of gas scenarios while scuba diving is like considering bringing a towel as a backup parachute while skydiving. It simply doesn't work like that.

I've been thinking about the "some gas is better than no gas" argument, and while I agree a SA would give you a couple of breaths and therefor would allow you to perform an extended CESA, a lot needs to line up in your favor for this to actually work in real life. Personally, I do not consider an extended CESA a proper ascent strategy, and "some is better than non" is a false perception of safety.
Unless you train CESA regularly, most CESA's are messy to start with, let alone if you absolutely need an extended one to get out a SHTF situation.
If you DO train CESA often enough, you will also be training gas awareness, so you actually are able to avoid the entire situation in the first place.
I guess risking a decompression injury or pressure injury (by performing a most likely messy extended CESA) is preferable to drowning, but why would anybody who is concerned about catastrophic equipment failure choose that as a backup strategy over making a safe ascent?

Keep in mind that running out of gas due to bad gas management is not a black and white event like you might have experienced during OWD training when the instructor closed the valve. Instead of sucking on a vacuum out of a sudden, in reality you feel an increase in breathing resistance, while you still have a few hundred psi left. This is a very noticeable feeling, and should be your (emergency) trigger to consider your ascent options (buddy? start ascending? deploy SA before actually needing it? ready 80 cuft stage?) and take it from there.

Even most real life equipment related out of air scenario's (like regs freezing) are manageable enough to do a safe ascent. Short of an exploding 1st stage while your buddy is too far and you don't have any alternate option there is really no need to consider an extended cesa a viable ascent strategy.

So if you want an alternate air supply, consider why you want it. Look at the scenario's you might realistically encounter, consider how you would like to ascent from those scenario's. Determine the amount of gas you need for those, and make an equipment decision based on that.
A couple of breaths? You must only get 50 breaths out of an al80.
 
There are several comments from people that I have come to have tremendous respect for, that don't believe that independent air sources are appropriate in "basic" diving. IMO, while buddy-diving is the "basic" standard, the reality is more complex and peoples' views are colored by their environment.

Personal, anecdotal results from my admittedly very limited experience ... in about 15% of 'buddy' dives I've been effectively a solo diver.

- Buddy just swam off and never looked back (actually that time I was having issues, fortunately only equalizing on a sawtooth tour dive.)

- Buddy separation in the murk several times, once surprisingly, a couple not. All too easy in the fall at Dutch where viz in the training area is terrible at baseline and goes to hell when it is packed like a Manhattan sidewalk at rush hour.

- Got tired of chasing an otherwise competent instabuddy flying high in the Coz current and chasing underwater squirrels ... (I did not ignore, but rather monitored her closely and positioned myself to be available to respond quickly.)

- Lake diving this last Monday - my buddy was bumping into me and I couldn't even see him (Ironic WRT this discussion - I was not actually carrying my pony since it was a < 20' bottom, CESA was a practical, "safe" option)

So now I carry a pony which gives me full redundancy of gas, valve, & 1st/hose/2nd. And additional time to sort out a problem for myself or others.

I have a 19cu.ft. for air travel or shallow dives and a 40cu.ft. for deeper stuff. My pony reg set is from the same family/performance as my main regs so acts as a backup/parts when traveling - I'd rather rent/borrow a reg for pony use. The 19cu.ft. was not that big a deal going to Cozumel and back - Bled it and removed the valve, rubber banded a plastic bag over it, shoved it checked-baggage. I asked before booking and the shop had no issue filling it for me.
 
Divers using an AL80, or even an AL 50 which I sometimes use for very shallow jetty dives, would be in no danger of running low on air if they checked their SPG every few minutes. That should be a cardinal rule of diving, giving warning of air consumption higher than anticipated and allowing the diver to adjust their plans to reflect the gas situation. I sometimes carry a small computer, but I rely on my SPG and wrist watch for dives <50 feet. How divers run out of air when they have a functioning SPG is beyond my comprehension. When I was young there were no computers and SPGs were not available. I was acutely conscious of gas usage and limitations, but had only a J valve to rely on. When I got my first SPG sometime in the 70s I thought it was the greatest thing ever invented for scuba. I've never changed my mind. I've never gotten a clear explanation of the reasons for not checking an SPG every 5 minutes or so. Running out of air when an unconsulted SPG has been indicating increasingly limited air remaining qualifies the diver for the Darwin award.
I have watched a person go from 1600lb to zero while they were looking at the gauge.
 
I often try to have it in my head, what I'll see when I next look at my SPG. Usually pretty darn close
That is my strategy too. I think what it is going to be before I look. If a DM asks me how much air I have, I tell them first, and then look.
 
That is my strategy too. I think what it is going to be before I look. If a DM asks me how much air I have, I tell them first, and then look.

I do that quite often as well but as much because I've just checked as anything else.

I prefer it when they figure it out and quit asking me.
 

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