Question re: Bailout bottles

[Jimmer]

Well Doc, I am registered as a Solo diver and actively dive solo. To stick more directly to the question, I used to own a 3.0 cf Spare Air and sold it off, as I felt it didn't have the volume needed, and chose to switch to the 30/40 cf bottle, partially for bailout during solo dives, and partially for use when I do my deco classes. Sy, if I was choosing between the 2 items you mentioned, I would definetly opt for the 6 cf bottle over the spare air any day.

 

[texdiveguy]

I just purchased the Spare Air 3.0 bottle and the H2Odyssey Extra Air Source 6.0 bottle. I will be returning one of them.

Realizing that these are "bailout bottles" for emergency use ONLY and not in any way meant to be an extra air source I would like to hear opinions from people who have them.

Thanks,

Sy

I have never used either of these 2 systems,,,IMO a larger traditional pony bottle is a better method of carrying and deploying contingency gas.

OP---if you just must keep one....go for the larger of the two systems.

 

[anytime]

I have tried the 3 cu/ft spare air from a depth of 100'. I got to 15 ft and 1 min in to the saftey stop before it ran out. I would go for the 6 cu/ft and try it out a few times to get the feel for how long it will give you before it runs dry.

 

[bogrady]

I struggled with this question myself recently. Based on the research I did on the boards, I was able to determine that with the 3.0 spare air, you are in serious danger just owning it, and with the 6.0 you are not in serious danger until you actually get in the water with it.

In the end, I took a serious look at the conditions I was trying to protect myself from and the limits I thought I was able to place on myself. The conditions/limits I defined were:

- No overhead or entaglement hazards

- No diving in locations I was not already familiar with

- Not planning on taking the time to problem solve, I'm just heading for the surface - I'll either leave the problem at the bottom or figure it out when I surface

- Never get close to NDL limits so the safety stop is optional. I always head up with at least 15 minutes of NDL time on my computer.

- 60' per minute ascent rate

I described my conditions/limits list to my LDS guy who owns both the spare air and the 6.0 and in the end he recommended I go with the 6.0 (the Zeagle Razr system). With this bottle, I believe my absolute limit is that I can get from 100' to the surface. In reality, I limit myself to 60-70'. The 3.0 just didn't have the volume to handle the depth.

I'll also relax some of the limits - like the need to be familiar with a location if the depth is less than 30'.

 

[markfm]

I ended up with a 19CF.

I did look at both Spare Air and the H2Odyssey, early on in diving. Not thinking solo really, at that time, but simple self-preservation

My choice for bailout was based on consumption. I wanted to be able to get up from depth, with safety stop, and a little margin for initial "oh, heck" huffing heavily.

You can check your own consumption, from several depths, diving an AL80. Write down your air pressure just before start of ascent. Write down the final pressure at the surface. The delta is what it takes to get up cleanly, with safety stop. Add a bit of margin.

(Realistically, I'm purely recreational, no deco, know that I could curtail my safety stop, but I don't want to have to. Given that I was going to spend the $ to buy something, I wanted enough for reasonable comfort.)

An AL80 is actually around 77 ft3. Here's the "PSI equivalent" for several possible bailout options:
19 ft3 -- 740
12 ft3 -- 468
6 ft3 -- 234
3 ft3 -- 117

If it takes me more PSI on an 80 than shown above, I have a problem.

I didn't bother looking at larger -- the 19 meets my personal criterion of the largest bottle I'm willing to schlep on vacation (and I do take it), as well as for consistent use (always when solo, and whenever it's deep even with a buddy).

Whatever you choose, practice with it so that it becomes second nature. I check my pressure before every dive, check the reg placement while in the water, top it off every few dives (small, but real, loss of PSI over time, due to just turning it on for diving then bleeding it when done).

 

[bogrady]

markfm - Thanks for doing the math on the "PSI equivalents". I'm going to use it when I graduate from my current 6ft3 bottle. I'm finding the hardest thing to do is to stick to the conditions/limits I set myself when I decided to go with the 6ft3. I get down to 60' - which is my self imposed safety limit on the 6ft3 and immediatly think - wow - that looks cool and its "just another 20 feet"

While I'm very happy with the 6ft3 - which answers the OP question - There is a 13 or a 19 in my future.

 

[Doc Harry]

Besides the discussion on volume, I think there should also be talk about a redundant regulator. In my mind, a Spare Air unit does not qualify as a redundant regulator, no matter what its volume.

Solo divers should be carrying a redundant regulator and air supply. In my mind, this means either: (A) doubles with an isolator manifold and two complete sets of regs, or (B) a single tank with a standard 1st & 2nd stage regulator setup AND a slung stage bottle (or attached pony bottle) with another REAL 1st and 2nd stage regulator attached.

If you do the math based on a stress SAC, a volume of 13 cubic feet is adequate for soloing down to 50 feet or so. For deeper soloing, a 19 cubic feet is necessary.

In my mind, a Spare Air would be fine to carry for standard buddy diving in case of unanticipated emergencies. The volume (either 3 or 6 cubic feet) may be adequate for an emergency ascent.

But for solo diving, I would not trust my life to a Spare Air unit even if it's volume was 80 cubic feet. I want a real regulator.

So, to answer your question: a solo diver needs something more than an "emergency" air supply, he needs a redundant air supply with redundant regulators.

To each, his own.

 

[-hh]

I ended up with a 19CF.

I ended up with a 13cf, but this was based primarily on easier warmwater diving. Had I been more intent on coldwater, I would have gone with a 19 or 30.

My choice for bailout was based on consumption. I wanted to be able to get up from depth, with safety stop, and a little margin for initial "oh, heck" huffing heavily.

You can check your own consumption, from several depths, diving an AL80. Write down your air pressure just before start of ascent. Write down the final pressure at the surface. The delta is what it takes to get up cleanly, with safety stop. Add a bit of margin.

The tricky part is the margin. SAC rates when stressed tend to skyrocket to 3x-4x normal consumption. Also, don't forget to add it some budget for time spent at max depth for sorting out whatever your OOA problem was and making the change-over.

An AL80 is actually around 77 ft3. Here's the "PSI equivalent" for several possible bailout options:
19 ft3 -- 740
12 ft3 -- 468
6 ft3 -- 234
3 ft3 -- 117

I like this ... its an effective way to illustrate the relative capabilities.

If it takes me more PSI on an 80 than shown above, I have a problem.

Here's some related text that I've lifted from the 1995 vintage rec.scuba FAQ, written by Nick Simicich (a former YMCA Instructor). I've interjected a few comments in blue:

How much air do you need to be safe?

The following chart was produced by Dave Waller, and presents a picture that I feel is conservative. You should probably assume that, in an emergency, you will be breathing at one of the higher breathing rates. It also assumes a 60 fpm ascent rate, which is considered too fast by many computer models and some training agencies. Therefore, these numbers should be considered minimums, and any deviation from these conditions would be likely to cause these numbers to increase.

Note the recommendations for using a stressed breathing rate, and that this model assumes 60ft/min ascent rate.

Philisophically, I'm of the opinion that if I'm going to spend a couple of hundred bucks for a bailout system, I'd want to be able to surface without also busting my dive computer's rules - - one less headache to worry about. This also builds in a bit of a safety margin in case things don't go quite right.



------------------------------------#------------------------------
-- -- Total consumption (ft^3) ---- # -- Total consumption (ft^3) -
-- without 15_ft Safety Stop (1) -- # with 15_ft Safety Stop (1,2)-
------------------------------------#------------------------------
--- Consumption rate (ft^3/min) --- # - Consumption rate (ft^3/min)
Depth| 0.50 | 01.00 | 01.50 | 02.00 # 0.50 | 01.00 | 01.50 | 02.00
-----+------+-------+-------+-------#------+-------+-------+-------
60ft | 1.66 | 03.32 | 04.98 | 06.64 # 2.75 | 05.50 | 08.25 | 11.00
80ft | 2.33 | 04.66 | 06.99 | 09.32 # 3.42 | 06.84 | 10.27 | 13.69
100' | 3.10 | 06.21 | 09.31 | 12.41 # 4.19 | 08.39 | 12.58 | 16.78
130' | 4.45 | 08.90 | 13.36 | 17.81 # 5.54 | 11.08 | 16.63 | 22.17
150' | 5.48 | 10.95 | 16.43 | 21.91 # 6.57 | 13.13 | 19.70 | 26.27
200' | 8.48 | 16.96 | 25.45 | 33.93 # 9.57 | 19.14 | 28.72 | 38.29


Notes:
(1) Total consumption includes 30 seconds at indicated depth, and a 60_ft/min ascent rate.

Note that another way of looking at this "30sec @ depth" assumption is half as long at twice the breathing rate, 1/3rd at 3x, etc. Given that the bailout is by definition intended to be used when there's an unexpected problem, I think that it is highly unrealistic to assume that one can rely on it always taking zero time with zero stress to accomplish any change-over


(2) Assuming a 1/2 consumption rate during a 15_ft safety stop for 3 minutes.

From the above summary chart, it is a bit of a hassle to recalcuate everything from a 60ft/min ascent rate assumed above to the more modern 30ft/min ascent rate. Its not all that hard to do, but overall, a new chart would be a lot easier to illustrate these values. You can pull it from the above with a bit of work. For example, for the datapoint of <130fsw @ SAC =1.0 with a 3 minute stop>, the derived total consumption value for a 30ft/min ascent rate would be: ((8.9-2.5)*2)+2.5+(11.08-8.9) = 17.48 ft^3.


-hh

 

[-hh]

For example, for the datapoint of <130fsw @ SAC =1.0 with a 3 minute stop>, the derived total consumption value for a 30ft/min ascent rate would be: ((8.9-2.5)*2)+2.5+(11.08-8.9) = 17.48 ft^3.

For those wondering, here's my "Formula Translation Cheater Guide" to the above:

((8.9-2.5)*2)+2.5+(11.08-8.9)
(ascent air)+30 on bottom)+(safety stop)

8.9 = (from table) Its the ascent time with the :30 on the bottom

2.5 = (calculated) air used in :30 on bottom at 130fsw at SAC=1.0
(ie, (1.0)*(5ATM)*(1/2 minute))

(8.9-2.5) = represents the air used just for the ascent at 60ft/min
((8.9-2.5)*2) = double the above, to make estimate for 30ft/min
((8.9-2.5)*2)+2.5 = add back in the bottom time air we had subtracted out

(11.08-8.9) = (both from table) the difference between these two values is the amount used on the safety stop. Add it in, since we started with just the 8.9 "without" value.

Thus:
((8.9-2.5)*2)+2.5+(11.08-8.9) = 17.48 ft^3.

BTW, if you don't like the original table's assumption that the SAC at the safety stop is half of normal, just add it in a second time. You would then get:

((8.9-2.5)*2)+2.5+(11.08-8.9)*2 = 19.66 ft^3.


-hh

 

[shadragon]

I have used the Spare Air 3. While it is an elegant and original design I feel it would be inappropriate using it any deeper than 40'-60' given my air consumption rate and its capacity. It is as you point out a "bail-out bottle" and not an alternate air source. I get about 35 breaths out of it in the pool. Never tried it in an ascent in open water.

For the few dollars more invest in a Pony and spare reg. I have an AL 40 which can bring me up from any recreational depth plus safety stop and still have a reserve left. Knowing this I can take my time, ascend slowly and control my breathing.

Safe diving...