Nitrox Spare Air

[O2BBubbleFree]

You guys have no imagination how to improve business.
I have the idea of a life time.
Since air and nitrox taste like .....nothing, how about a cherry flavoured spare air?. This way the one more breath will taste like something and if it's the last, than at least your last breath will be sweeeeeet.
If it finds acceptancy, you could expand into other flavours too.

How 'bout throwing in some breath freshner, so that the boat crew won't object so much when it comes time to give you CPR?

 

[Uncle Pug]

Number one reason not to carry a SpareAir:
You immediately identify yourself as someone who is planning to have one or more of the 21 reasons for being OOA.

 

[-hh]

Hmmm... I'm a Naval Aviator, active duty from '69-'91; never saw a spare air there.
Rick

It wasn't for fixed wing, but for Helicopters. It was known as the "HEED" (Helicopter Emergency Escape Device).

Spare Air did have the USN contract for awhile, but lost it to...IIRC...US Divers, who had a 2.5ft^3 bottle with a regulator on a short whip...the Micra?

Apparently, one of the Navy's revised selection criterion had to do with the SA bottle/regulator's design, which had an unpleasant tendency that it would provide the leverage to knock teeth out of the mouth of the crew if they tried to deploy the HEED as the chopper was going down (eg, before water impact).


-hh

 

[SueMermaid]

My dive club bought a spare air back in the early 90s. Why? I dunno. The club then dissolved. I inherited it as the last member of the club. I asked them if they wanted it, nobody did. So I listed it on Ebay a month ago. It was out of hydro, mind you, and I still got $120 for it.

I think therein lies the value. Resale.

 

[-hh]

Depends how long it takes you to react. Have you ever had a 1st stage o-ring blowout?

I've yet to have that pleasant experience. However, I have read the analysis of a Spare Air "Testimonial" by Undercurrent magazine. Fortunately, they've left it online:

http://www.undercurrent.org/UCnow/articles/SpareAir9902.shtml


This evaluation started because SA testimonial #67 claimed an extremely rapid tank vent as the result of a swivel on an HP hose. Unfortunately, it neglects the fact that all regulators sold since at least 1982 have had a restriction orifice that generally prevents you from losing more than 50psi/minute.

Nevertheless, they do try to reproduce the testimonial's "<30 sec" claim, resulting in the following test, which is probably an even worse case than a 1st stage O-ring blowout:

"Okay, then how about just flat-out opening up a tank valve on an aluminum 80 with nothing whatsoever attached to it? Nope, it still takes almost two minutes to go from 3000 psi to zero."




-hh

 

[PhotoTJ]

Wonder if you could do it if you somehow managed to blow the valve - tank o-ring?

 

[-hh]

Wonder if you could do it if you somehow managed to blow the valve - tank o-ring?

It might not make any significant difference.

In plain english, the maximum flow rate of a gas through a restriction is a function of how much pressure and how narrow the restriction is. But what makes this "tricky" is that the proverbial "speed limit" through any restriction is Mach 1, which times the area of the restriction equates to a mass flow rate. Therefore, for a given restriction size, there's a hard limit that cannot be exceeded no matter how much higher the gas pressure is.

For the hardcore techies, I'm referring to when a nozzle's throat hits its choke value.

What this means is...

if:

(the tightest part of a blown tank o-ring's "escape path")

is equal to or less than

(the tightest part of an open-valve's "escape path"),

...then the flow rate can only be equal to or less.


If this is true or not is a pretty good question. However, my hunch is that since O-rings generally need to be well supported, I don't think that its that likely that the tank o-ring will be able to crease a larger path than the one that was designed to be present within a tank valve. But I do admit that this is just a guess.


-hh

 

[jonnythan]

You could do it if your first stage blows apart underwater.

 

[miketsp]

I've yet to have that pleasant experience. However, I have read the analysis of a Spare Air "Testimonial" by Undercurrent magazine. Fortunately, they've left it online:

http://www.undercurrent.org/UCnow/articles/SpareAir9902.shtml

This evaluation started because SA testimonial #67 claimed an extremely rapid tank vent as the result of a swivel on an HP hose. Unfortunately, it neglects the fact that all regulators sold since at least 1982 have had a restriction orifice that generally prevents you from losing more than 50psi/minute.

Nevertheless, they do try to reproduce the testimonial's "<30 sec" claim, resulting in the following test, which is probably an even worse case than a 1st stage O-ring blowout:

"Okay, then how about just flat-out opening up a tank valve on an aluminum 80 with nothing whatsoever attached to it? Nope, it still takes almost two minutes to go from 3000 psi to zero."

-hh

The consensus of nearly 2 mins to empty an AL80 from full has been well discussed in the past:
http://www.scubaboard.com/showthread.php?t=46984&page=1&pp=10

When it happened to me I wasn't starting with a full tank and the air didn't have to pass through any small orifices in the regulator. The post o-ring practically disappeared. It probably took me a good 10-15 seconds to react to the noise and my SPG dropped very fast. As you say there may have been a pressure gradient across
the post with a lot more air in the tank than the SPG was indicating.
But I can assure you that if you're at depth with that noise behind your head and an SPG near zero you do not feel like estimating how much longer it will bubble.

 

[Chris Hipp]

Please forgive my laziness if this has already been said:

Could it be that the nitrox spare air is just a marketing gimmick trying to get all those dumb dumbs that think you use less air when using nitrox? Ya know, the guys that say "Man I need to get nitrox cuz I burn up a tank in fifteen minutes."