Spare Air - Sorry!

[RalphPorter]

It certainly is an emotive subject isn't it

I sense that naturally enough everyone wants to answer the question in the context of the diving they do and maybe not so much in the context of the question, this from UaVaj is interesting:

IMHO
0-33' = 3cf
34'-66' = 6cf
66' - 99' = 12cf
100' - 133' = 24cf

Maybe that is a little more subjective. I read several times that the maths don't lie so from my point of view with the same parameters as before (my diving < 60' reef daytime clear water no overheads etc) and using the table kindly provided earlier in the thread it seems reasonable that a 6cu would be beneficial given that the maths say I could do an ascent under the maximum rate from 60' at triple the normal SAC rate (is that reasonable in a stress situation) and use 75% of the supply, safety stop aside of course. I guess the argument that you could potentially always need more air is clear, but still that's true if you carry 19, 30, 40, if a big rock fell on you and pinned you to the bottom how much would you need while you buddy went to find a jack or something

I would like someone to explain something to me here though in case I've messed up the calculations, the parameters for spare air 3cu in the spreadsheet were given as tank volume 0.375 litres but the tank volume on the 6cu is apparently 0.9 litres which is more than double, confused about this. I plugged in as below:


ENTER DATA Notes:-
SAC= 75 Lit/min UK Average Air Consumption= 25 L/min
Tank Vol= 0.9 Liter SPARE-AIR Volume = 0.375 Liters
Tank Pressure= 207 Bars SPARE-AIR Pressure = 207Bars
Ascent Rate= 18 m/min PADI Max Ascent Rate = 18m/min
Available Gas= 186.3 Liter SPARE-AIR Contents(USA)=2.7cuft@3,000psi

Depth(m) Asc.Time(min) Avg. Amb. Press. Gas Consumed(L) % of Tank Used
2 0.11 1.10 9.17 4.92%
4 0.22 1.20 20.00 10.74%
6 0.33 1.30 32.50 17.44%
8 0.44 1.40 46.67 25.05%
10 0.56 1.50 62.50 33.55%
12 0.67 1.60 80.00 42.94%
14 0.78 1.70 99.17 53.23%
16 0.89 1.80 120.00 64.41%
18 1.00 1.90 142.50 76.49%
20 1.11 2.00 166.67 89.46%
22 1.22 2.10 192.50 103.33%
24 1.33 2.20 220.00 118.09%

Thanks

Ralph.

 

[TSandM]

I think your math is probably right -- my calculations would be about 10 cf of gas for an ascent from 60', but I don't calculate for the maximum ascent rate (20 meters/min).

Again, the underlying question is: Is this device necessary at all? Is it cost-effective? If a device is necessary, is there a more effective or less expensive solution?

I again posit that, given the situation you have described, of diving with a known buddy who is mindful of her gas supply and who practices emergency procedures, no device is necessary for the dives you describe.

Should you CHOOSE to provide yourself with redundancy, I believe there is a more cost-effective solution, which is an auxiliary tank with enough gas in it to permit an ascent at a normal ascent rate -- and also give you a little time to cope with whatever made you bail out to that gas supply. (Get buddy's attention? Secure unusable regulator to avoid getting tangled in kelp?) In addition, as I pointed out some time ago, the resale value on a spare first and second stage, and a bottle which could have multiple uses, is much higher than the resale value on a Spare Air.

 

[UaVaj]

All those math equations are only good for controled labortory conditions. Under depth / real condition - those math equation are useless. It will never happen like those equations under depth. Mark my words.

My profile is typically 130' without no overhead and I carry a 23cf. According to my actual downloaded dive log. I am averaging 15cf ascending from that depth with a safety stop. This is a "non stressed" ascend consumption. I can only imagine the difference of a stressed out ascend consumption. Sometimes I do feel like my bail-out bottle should be be bigger.

 

[Rhone Man]

Most of the people who I know who have spare air don't actually use it for diving. They either (i) keep it on their boat, in case they run over a fish trap, so they can cut the line loose from their prop shaft, or (ii) they use it for cleaning awkard spots in their swimming pool. It is extremely useful in both cases.

But I do know one guy who uses his for diving and he professes to be very happy with it. Horses for courses, I guess.

 

[DevonDiver]

Andy, I think I know where you are coming from, but I don't agree. As I've previously mentioned, the SA device isn't ideal or even the correct one in all circumstances. It does however provide a credible secondary air source for the OP, under the conditions described. To say that any piece of equipment is unsuitable across the board just isn't substantiated and certanly can't be deemed to be a fact.

My logic is that the SA only provides sufficient air for ascent at depths which would ordinarily be easily accomplished with CESA.

Furthermore, adding SA as an option in those scenarios (shallow dives) only serves to complicate and delay a diver's emergency reaction.

We've already seen one thread contributor citing their plan "to use SA to locate their buddy underwater if OOA". That's a good example of how it creates a false sense of confidence that has a severe negative impact on emergency management.

SA has in-fact saved divers lives.

Spare Air has been used for emergency ascent. Chances are that those divers could have conducted a CESA anyway..and lived. Obviously the SA marketeers don't mention that when they cite their statistics.

I'm happy to do an ascent on 200 litres of air that "requires 600 litres." In an emergency ascent, there is no rule that says that you have to breathe continuously. I'm happy to accept one more breath of air in any situation where none would be otherwise available.

This is very true. Some air is better than none. Especially if you are a highly experienced diver, with ingrained emergency reactions and a high tolerance for air starvation and equally high panic threshold....

However, my definition of an appropriate redundant air source is one which provides sufficient gas to reach the surface as a normal ascent. That should be regardless of the skill, experience and physical capacity of the diver concerned.

An appropriate redundant air source ends the emergency there and then. You have ample air and conduct a normal, but immediate, ascent.

An inappropriate redundant air source continues the emergency. You have insufficent air for a normal ascent, thus are still forced to conduct a CESA with intermitent breaths.

Now.... I would still argue that SA is an inappropriate redundant air source. It can only supply sufficient air at depths where redundant air is not required. However, we can split hairs and I could agree that it was feasible as a "CESA Assist" device. BUT...(and a big BUT)... if it is used as a 'CESA Assist'... then it must not provide any other delays to the divers' CESA reaction...and the way it is marketed and advertised does exactly that.

 

[irishsquid]

...Some air is better than none...

Someone had a Sig Line related to that; some thing about breathing a fart from a donkey's ass if it got them to the surface. Bob; I think it was. But, I'd bet no one would seriously WANT to be in that situation. SA is better than a donkey's fart and a pony is better than a SA. (Pony BOTTLE) that is, not a pony fart.

 

[DevonDiver]

Hi JImi,

Some air is better than none - but not if:

1) It leads the diver into delaying their emergency ascent due to false expectations.
2) It causes a dangerous level of complacency, decreasing overall dive safety.
3) It causes a delayed panic reaction once that complacency is shattered.
4) It is marketed as an 'emergency solution' when it is not, leading to false expectations.
5) Better alternatives are available, but the diver is 'encouraged' not to source them.

 

[SCUBA482]

Lots of good info here and as you can see the SA just isn't the BEST option available IMHO. I concede to the notion it is a lot more convienient, but at what cost?

I use a 19cf pony back mounted to my tank. I have a yellow hose, 2nd stage, and button gauge that I use just for my pony rig. Since I dive with a Scubapro Air2, I eliminated my octo on my primary 1st stage thus only two 2nd stages on my right side to chose from. I charge the line then shut off the valve until I chose to deploy my pony setup (which is clearly marked yellow as mentioned). This method has prevented my "accidental" use during the beginning of my dive and not given me any problems. Furthermore, I also deploy it on my final dive to ensure competency. I will add though that I do not attach my pony rig unles I dive below 60 fsw.

I'd like the OP to consider cost effectiveness as well. As mentioned, the full pony setup with a 1st, 2nd and button SPG is not much more money than the SA. I looked as well when I first started. I don't notice the pony at all while diving and find it useful during S&R dives while using a lift bag or smb. Try deploying a SMB while breathing off your A2 during an ascent on a drift dive when you may need to vent air from your BC. Makes things much easier to use pony reg for said tasks. I mention this since you may expand your diving interests and this is another good use of a pony system if you have an A2 type of setup.

Finally, I wish my wife would dive but it's not going to happen. I know if she did I would feel compelled to ensure her safety. I'd hate to leave her UW while I was on the surface so I'd opt to deploy pony and locate her to end our dive (depth and air permitting in pony of course). Not saying anything about genders here, just like any good buddy we should be taking care of them as well. Guess that comes from a self sufficient mindset. I believe a pony offers aids in your abilty to increase your self sufficiency, again IMHO.

An interesting perspective that I had not thought is the traveling with the SA v Pony. If travelling, I dive with my son or in the "herd" and there is ALWAYS somebody close (too close if you ask me) thus reducing my need for the pony or SA. I'll also add that I prefer to travel to clear warm water destinations for vacation so the conditions will most likely be better than here in California where I dive regularly. Having said this, practice good buddy skills by staying close, checking your air regularly and asking your buddy for his/her air remaining so you avoid the OOA and know when to turn a dive (rule of thirds). This is all part of the dive plan isn't it?

Whatever you decide, it doesn't matter what you strap on for your potential Murphy moment of OOA, just think..if it hit the fan do I want a little insurance or adequate insurance to handle the task. You may only get one chance at it!

Good luck!

 

[halocline]

Why is everyone so seemingly worried about running out of air? That's the question that should be answered.

The idea that an alternate air source, regardless of its size, is somehow a substitute for a missing buddy is pretty troubling. There are problems encountered underwater FAR more likely than suddenly running out of air. A serious cramp, nausea, disorientation, entanglement, anxiety, loose tank, loss of buoyancy, etc....a bailout bottle solves NONE of those problems, yet people routinely think that carrying one increases their safety because they 'might' get separated from their buddy.

Safe diving is one thing, use of bailout bottles is another, and the relationship between the two is more complicated than most people care to acknowledge.

 

[Chris12day]

Why is everyone so seemingly worried about running out of air? That's the question that should be answered.
QUOTE]

Because we do not have gills and must breath under water? I dive all over the world. I have insta-buddies. Am I willing to risk my life on that insta-buddy? NO WAY!