Problems with Spare Air?

[Bart]

Im looking to buy a Spare Air and was wondering how reliable they are,and if anyone has anything negetive to say about them.
Also I was wondering, where is a handy place to mount them?

Thanks
Bart

[texdiveguy]

Originally Posted by Bart

Im looking to buy a Spare Air and was wondering how reliable they are,and if anyone has anything negetive to say about them.
Also I was wondering, where is a handy place to mount them?

Thanks
Bart

Bart... you might do a search on this topic here and over at Scuba Board....there are many threads about just this subject.

I can't say anything good about the Spare Air system.....so I will just leave it at that.

PS--- get a pony bottle set-up!!

[navyhmc]

IMO, the spare air is a good bail out for less than 60'. It is intended for something to get you to the surface-that's about it. 6 cubic feet of air is not a lot of air. At 60' and a SAC of .75 cfm, if the diver is at 60' for 30 seconds getting things set and then starts to ascend, he/she will use about 3 cubic feet to get to the surface-good to go, right? Add a safety stop because the OOA incident happened at the NDL and you're down to literally 30 seconds of air left to ascend the last 15' after a safety stop.

Add additional depth to the scenario and you may have trouble. drop the depth to 90' with the same 30 seconds to get set for ascent. You used 1.5 cubic feet for that 30 seconds, 25% of your volume. the ascent to 15' for a SS will take roughly 1.5 min (Though in real life it would be faster, but bear with me.) that will use up 3 cubic feet of the spare air. Now you do not have enough for a safety stop if needed.

The good news is you will make the surface, the bad news is that you are at greater risk of DCS. This is also not taking into account that one's normal SAC rate is out the window when you figure that you will be a little paniced and without any PSI in your tank, you can't inflate your BC for aid in ascent if needed so there's additional work load as well.

I think that a spar air is good for shallower depth, but anything below 60' a pony will be better-13 cu ft minimum, 19 cu ft is better.

YMMV but that's my thought.

From what I have noted, the spare air system is reliable enough in it's own right, but the available air is the issue.

ETA: I was thinking that the spare air was 6 cu ft, halve the figures above and you can see why below 60' I wouldn't recommend it. The only thing it would be good for is to give you some breaths during your emergency ascent.

[Crimediver]

Navyhmc nailed it. I have a spare air. I don't use it for diving. Get a pony if you need a bailout.

[MSilvia]

If you need to bail out of a crashed helicopter or overturned kayak, Spare Air is the ticket. For diving, it isn't really an adequate backup, and I don't have much good to say about them as an emergency device for divers. I'd recommend a 19 cubic foot (or greater) pony tank too.

[DarinMartell]

I bought the Spare Air before I was even certified because I wanted a redundant Air source since I knew most of my buddies would be strangers assigned to me and I wouldn't know their dive styles. For the record my instructor / owner of the LDS said the same as what others have already said. I used it twice in open water and a handfull of times in the pool. I never had any problems with it. However after reading the many threads here about Spare Air vs. Ponies I sold my Spare Air on E-Bay.

On sale Spare Air in around $200. By doing my research, between price matching, our 10% discount, and the gift cards I earned on Scuba Toys I was able to get a 30CF pony, and Mares Regulator set for the same price.

[charlesml3]

I thought Spare-Air was only three cubic feet?

At any rate, I have two pony tanks. A 6 foot for shallow dive locations and a 13 for the deeper ones. I really don't want anything bigger than that because it gets to be a pain on the airplane.

-Charles

[No Misses]

Spare Air or Pony?
The question that you need to ask yourself is, "What do I need/want this for"?
IMHO, If you are worried about having an OOA (Out Of Air) situation in less than 60 fsw. You can easily do a CESA (Controlled Emergency Swimming Ascent). If, on the other hand, you are planning on doing dives where entanglement, overhead environments, and/or depth might be an issue; a spare air does not give you a lot of time to resolve these situations.

There is some simple math that you can use to figure out what capacity is needed for emergencies.

Let's say that your SAC (Surface Air Consumption) is .6 cf/min (cubic feet per minute)
Your planned dive is 66 fsw (3 ATA) on a wreck where entanglement in monofilament fishing line might be an issue. How many minutes of "Spare Air" will you need to get free of the entanglement and surface?

SAC .6 cf = 1.8 cf at 66 fsw (Gas at depth of 3 ATA is more dense than at 1 ATA)

Small Spare Air is 1.7 cf
1.7/1.8= 0.9 minutes to get untangled and surface

Large Spare Air is 3 cf
3/1.8 = 1.7 minutes to get untangled and surface

13 cf pony bottle
13/1.8 = 7.2 minutes to get untangled and surface

19 cf pony bottle
19/1.8 = 10.5 minutes to get untangled and surface

How much time do you need/want?

Please note that I rounded off some of these numbers. Your Air Consumption will not stay at 1.8 cf/min. When you ascend to 33 fsw your consumption will be lowered to 1.2 cf/min. Also I used .6 SAC as a common reference. Your SAC may be higher or lower. Keep in mind that if you are stressed and strugling, your SAC will be higher than normal. I used 66 fsw for this example. You can put in any depth that you want. At 130 fsw your consumption will be ~5x SAC. SAC is calculated for the surface or 1 ATA - to calculate consumption at depth just multiply by your ATA.

I hope this helps with your decision.

[MSilvia]

Originally Posted by charlesml3

I really don't want anything bigger than that because it gets to be a pain on the airplane.

Wow... if I lived in North Carolina, bringing my gear on a plane would be one of the last things I'd be worried about. Some of the best wreck diving in the world is right in your back yard!

[No Misses]

I am bored today. So, here is a graph showing minutes of air at different depths with different size cylinders. I still used .6 SAC for the calculations.