Main Menu
Join Undercurrent on Facebook

The Private, Exclusive Guide for Serious Divers Since 1975 | |
For Divers since 1975
The Private, Exclusive Guide for Serious Divers Since 1975
"Best of the Web: scuba tips no other
source dares to publish" -- Forbes
May 2001 Vol. 16, No. 5   RSS Feed for Undercurrent Issues
What's this?

Is A Spare Air Wo rth It?

how to ensure you’re not the next victim

from the May, 2001 issue of Undercurrent   Subscribe Now

Cylinders providing extra air for emergencies come in three basic forms: A small bailout bottle (like Spare Air), a pony bottle (a larger bailout bottle) and independent twins, which technical divers also use to provide all the gas they need to make a dive.

Ponies, which attach to the main cylinder by various bands, hold from 6 to 500 cubic feet of air, although with the higher amount one might just as well use standard size independent twins. Small bailout bottles, like Spare Air, typically attach to the BC and come in sizes from a tiny 1.2 cu. ft. to Spare Air’s 6 cu. ft. “600-Twin,” and are connected to the BC via Velcro straps, holsters or lanyards. Spare Air sells three rigs. The least expensive 3 cu. ft. lists for nearly $300 and the Twin approaches $500 (a sum that can also buy you a decent pony or independent doubles set-up and lots more air). The small Spare Air cylinder comes with a built-in regulat or.

For deeper recreational diving, and some technical diving, a pony bottle is the best bet. The question here is whether there is a value, at all, to the Spare Air.

For dives above 60 feet, the largest Spare Air should suffice for an emergency ascent. Spare Air advertises 30 surface breaths for the 1.7-cu. ft. unit, 57 for the 3 cu. ft. and 144 for the Twin 3-cu. ft. set-up. But, that’s on the surface. What about in an emergency, when one is down a few atmospheres and breathing hard?

Depending on breathing rate, to ascend from 60 feet at a brisk 60 feet per minimum without a safety stop requires anywhere from 2-7 cu. ft. of air. From 100 feet, it’s from about 3 cu. ft. to more than 12 cu. ft. Given the likelihood that consumption rates will be greatly elevated in an emergency out-of-air- situation , the average diver could expect to have enough air to make it quickly and directly to the surface from around 60 feet. Surely there is something to be said for this.

Is A Spare Air Wo rth It?

Of course, such an ascent rate without a safety stop is an open invitation to DCS. For a slower ascent and 15-ft. safety stop for three minutes, you’ll need proportionately more air, far more than afforded by the most generous Spare Air at any depth. For this reason, it is important that a diver carrying a Spare Air not be lulled into a false sense of security. Once in trouble, he will have scant time to solve problems or even make himself positively buoyant.

Some in the dive community who have tried a Spare Air, complain about the lack of it. Leaking from the regulator is the most frequently heard disgruntlement. Bob Parks told Undercurrent that his Spare Air lost air between dives. “While on a live-aboard last year, the spare air would lose about one quarter of its contents over a period of about four hours. I sent it back to the office in Huntington Beach, CA and they fixed the problem, gratis.” Don Latta (Chicago) said his “Spare Air would fill and seemed okay, but the pin gauge would show half full at the end of the day. Slow leak. Sent unit back; out of warranty and over $100 to repair it. Eight months later I checked before a trip and a faster audible leak this time. Spare Air fixed it for half price and says my problem is that I am not storing with bottle pressurized. After I return from the trip, I fill the bottle at the dive shop, however, before my next trip the bottle is empty again. I fill it at a shop to check integrity; and air comes out almost as fast as it is going in. Along the line, I lost the little screw that acts as a relief valve on the filler gadget and didn’t have time to locate the part; I bought a second filler for $45. Not a good experience for a pretty cheap guy, but mainly I got to the point were I just didn’t trust the thing. Incidentally, both dive shops I deal with refuse to carry the things or be involved in repairs . ”

Because some shops don’t want to deal with Spare Air, this often means the inconvenience of sending it back to the manufacturer, with shipping and handling charges both ways going on your tab. Dean Michaels, who works in Florida, says, “I’ve been repairing Spare Airs for three years and have seen hundreds of units that wouldn’t hold air, even after they just got back from servicing. In all but a few cases it was a matter of lack of service by the owner (“if it ain’t broke, don’t fix it”) or poor service by someone who didn t have a clue what to do. Most people seem to think a Spare Air requires the same amount of service their tank and valve needs (none). That’s not the case. It is a special use tool that needs to be checked regularly and serviced before it is needed by someone that knows what they’re doing . ”

Air Required to Surface Safely

Total consumption
Without 15-ft.Safety Stop
Depth 0.5 1.0 1.5 2.0
60 1.66 3.32 4.98 6.64
80 2.33 4.66 6.99 9.32
100 3.10 6.21 9.31 12.41
130 4.45 8.90 13.36 17.81
150 5.48 10.95 16.43 21.91
200 8.48 16.96 25.45 33.93
Total consumption
Without 15-ft.Safety Stop
Depth 0.5 1.0 1.5 2.0
60 2.75 5.50 8.25 11.00
80 3.42 6.84 10.27 13.69
100 4.19 8.39 12.58 16.78
130 5.54 11.08 16.63 22.17
150 6.57 13.13 19.70 26.27
200 9.57 19.14 28.72 38.29

Notes: All consumption rates assume a 60FPM ascent rate; total consumption includes 30 seconds at indicated depth
and assumes 1/2 consumption rate during a 15-ft. safety stop for three minutes.(Thanks to David Waller for this table.)

So, if you don’t want to tote a Spare Air, consider one other source of air for an emergency: your BC. Air in the BC from the tank contains 21% 02 and 16% if orally inflated. Studies by the YMCA show that air added to a BC can be rebreathed 13 times or more without becoming overly hungry for fresh air. While the technique is not difficult, it does require some brief instruction and practice. Interested readers are directed to the September 1999 issue of Undercurrent for a detailed description of the technique.

Remember, these devices and techniques are nothing more than emergency sources, and not ways to extend dive times. The confidence provided by carrying an alternate air source does not absolve the diver from monitoring his air supply. There is no reason to run out of air in non-emergencies, air that is your buddy’s as well as yours.

-Doc Vikingo

I want to get all the stories! Tell me how I can become an Undercurrent Online Member and get online access to all the articles of Undercurrent as well as thousands of first hand reports on dive operations world-wide

Find in  

| Home | Online Members Area | My Account | Login | Join |
| Travel Index | Dive Resort & Liveaboard Reviews | Featured Reports | Recent Issues | Back Issues |
| Dive Gear Index | Health/Safety Index | Environment & Misc. Index | Seasonal Planner | Blogs | Free Articles | Book Picks | News |
| Special Offers | RSS | FAQ | About Us | Contact Us | Links |

Copyright © 1996-2022 Undercurrent (
3020 Bridgeway, Ste 102, Sausalito, Ca 94965
All rights reserved.