Spare Air on deep but no deco dives??
- Thread starter ReadyDiverOne
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
caruso
Banned
This article proves that a 3 cubic foot Spare Air is enough gas to get a diver to the surface from 100' which is opposite of what it says at the bottom of the article which contains two statements that are just plain nonsensical.
1) For a three-minute safety stop, you’ll need another 2 cubic feet of air.
2) it should take you about 3 minutes to get to the surface if you maintain a nice controlled ascent rate of 30 feet per minute. Yes, it’s twice as slow as what you probably learned when you took your open water class, but for extra safety, 30 feet per minute is recommended.
No diver with his or her mental faculties intact is going to, in an out of air emergency at 100', going to 1) ascend at a "slow recommended rate which his half of what was taught in open water class" nor will the diver 2) sit at an optional safety stop 15' for 3', it's simply ridiculous to even consider that they would do such a thing in that situation.
The article also assumes an abnormally high SAC rate which probably does not apply to most divers. It also doesn't account for the fact that we can stretch a few remaining breaths of air because as we ascend the air in our lungs expands and we can exhale slowly to vent the increasing volume of air in our lungs.
So once we remove the stupidity from the equation in the linked article, and revisit the final statement in the article: which is "You need 8.5 cubic fee of air" we can subtract the 2 cubic feet calculated for the safety stop and half the remainder due to the faster ascent rate and you get almost exactly the contents of the large model of spare air which is 3 cubic feet. Even if we assume an excessive SAC rate and don't account for releasing the gas slowly to conserve it. 'Nuff said.
drrich2
Contributor
Quick Googling didn't turn up a source, so going on memory here. IIRC, I've read a report from someone who simulated an OOA situation with a Spare Air 3 at around 90 feet deep; looked around quickly to simulate the natural response to a surprise loss of primary gas supply, then ascended. From what I recall, the SA wouldn't last all the way up for a controlled, properly slow ascent to 15 feet, a full 3 minute safety stop and a properly slow ascent to the surface.
That said, 3-cf air sounds a lot better than none. Ascent should be slower, allowing for safer off-gassing, and I would imagine stress & anxiety levels significantly lower.
It's my understanding a Spare Air 3 at the surface gives roughly around 45 or so breaths (which is about what I counted emptying it for travel).
That said, I use it as a redundant air source in some solo diving situations. The gas supply is much more limited than a pony bottle. My thinking:
1.) It's way lighter, more compact & just more likely to go with me in luggage than my 30-cf pony with separate regulator. I bought an H2Odyssey setup with 6-cf pony that I've never gotten around to getting going (killer deal on pre-owned).
2.) I'd rather have 45 breaths (or pressure-reduced amount) at an OOA situation at depth than none.
3.) I don't usually solo dive 90 feet deep!
The OP seems interested in whether having a SA 3 is a worthwhile 'extra redundancy' measure when doing recreational deep buddy dives with (I presume) reasonably good buddy practices and diligence to monitoring gas supply. General community practice suggests it's not thought needful, and a diver who loads up on dubious peripherals is sometimes said to look like a Christmas Tree from all the 'dangling' stuff.
But it's not a huge deal if you want to carry one.
Richard.
That said, 3-cf air sounds a lot better than none. Ascent should be slower, allowing for safer off-gassing, and I would imagine stress & anxiety levels significantly lower.
It's my understanding a Spare Air 3 at the surface gives roughly around 45 or so breaths (which is about what I counted emptying it for travel).
That said, I use it as a redundant air source in some solo diving situations. The gas supply is much more limited than a pony bottle. My thinking:
1.) It's way lighter, more compact & just more likely to go with me in luggage than my 30-cf pony with separate regulator. I bought an H2Odyssey setup with 6-cf pony that I've never gotten around to getting going (killer deal on pre-owned).
2.) I'd rather have 45 breaths (or pressure-reduced amount) at an OOA situation at depth than none.
3.) I don't usually solo dive 90 feet deep!
The OP seems interested in whether having a SA 3 is a worthwhile 'extra redundancy' measure when doing recreational deep buddy dives with (I presume) reasonably good buddy practices and diligence to monitoring gas supply. General community practice suggests it's not thought needful, and a diver who loads up on dubious peripherals is sometimes said to look like a Christmas Tree from all the 'dangling' stuff.
But it's not a huge deal if you want to carry one.
Richard.
StefinSB
Contributor
[QUOTE="caruso, post: 8372976]
The article also assumes an abnormally high SAC rate which probably does not apply to most divers. It also doesn't account for the fact that we can stretch a few remaining breaths of air because as we ascend the air in our lungs expands and we can exhale slowly to vent the increasing volume of air in our lungs. [/QUOTE]
Why is a SAC of 1 cft/min abnormally high for an out of gas and most probably very excited diver?
The article also assumes an abnormally high SAC rate which probably does not apply to most divers. It also doesn't account for the fact that we can stretch a few remaining breaths of air because as we ascend the air in our lungs expands and we can exhale slowly to vent the increasing volume of air in our lungs. [/QUOTE]
Why is a SAC of 1 cft/min abnormally high for an out of gas and most probably very excited diver?
Landlocked123
Contributor
I have a 19 and a 30. I have never dove without one or the other. Dives up to 60 feet its 19. Dives deeper than 60 its the 30. I recommend the 30. In a real emergency situation, which I have experienced only once it was great knowing I had the 30 on me. The buoyancy difference to the 19 is almost non existent. Save the money, forget the spare air, get a 30 and never look back. For dives up to 100 feet it should be all you ever need. Regarding the 40 if you are considering a jump into tec go with the 40 as others have mentioned. I think its not needed but if you jump to tec down the road I believe its what most tec divers use as a deco bottle for o2
Another negative nod for spare air. It simply does not have enough capacity.
PfcAJ
Contributor
Learn to dive in a buddy team.
Manage your gas.
Skip out on unnecessary gear.
Manage your gas.
Skip out on unnecessary gear.
A 13cuft is quite travel friendly and will provide a safe accent with most if not all of a safty stop.
I just use it in place of my left sm tank when single tank, resort diving.
A full size (accurate) spg lets you monitor consumption to the last few bar.
I get the buddy thing but adding a layer of self reliance is how I dive.
Cheers, Kevin
caruso
Banned
As we ascend, the gas in our lungs expands. I think that's universally understood. So if a diver is ascending from depth he or she doesn't need to be huffing and puffing on their regulator, they can take slow breaths and just allow the expanding gas to vent from their lungs which gives them a lot more mileage out of what gas remains in their tank.
Lets assume the SAC rate of 1 is perfectly normal for every single diver in an out of air situation. It's a bit extreme but my point is that according to the linked article if a diver ascends at 60 feet per minute and does not do a safety stop the Spare Air will be sufficient even at a SAC rate of 1.0
Similar threads
