Switching gasses at depth?

[Sonic04GT]

When I return to the states I will be getting Nitrox certified and dive that primarily. However, I have the standard Spare Air. Say there were an emergency and I had to use it, would it be ok to just switch over to normal Air from Nitrox? I saw that they have a Nitrox model now...

I'm a rookie but the only real concern I saw was that you've already been down past the allowable bottom time for Air and go into Deco. In emergency situations though, would this be ok just to get back to the surface slowly?

Then again, what if I'm diving Nitrox and my buddy is diving Air and I had to buddy breathe with him...? How often are you matched with the same gas as your buddy?

 

[bamamedic]

When I return to the states I will be getting Nitrox certified and dive that primarily. However, I have the standard Spare Air. Say there were an emergency and I had to use it, would it be ok to just switch over to normal Air from Nitrox? I saw that they have a Nitrox model now...

I'm a rookie but the only real concern I saw was that you've already been down past the allowable bottom time for Air and go into Deco. In emergency situations though, would this be ok just to get back to the surface slowly?

Then again, what if I'm diving Nitrox and my buddy is diving Air and I had to buddy breathe with him...? How often are you matched with the same gas as your buddy?

I'm no expert...but I've got an opinion on almost everything

Generally, I think it would be safe to switch over to your air-containing Spare Air from Nitrox, since the Spare Air is only used for an emergency ascent. If you were to switch over from Nitrox to air for a significant period of time (say, if you were using a pony bottle containing air to extend your underwater time) then you'd have to factor that into your dive plan because of the increased nitrogen content of air vs. Nitrox. However, since you're only using the Spare Air in an emergency, your time on it will be limited to just a few minutes, and you're on the way up anyways, so the increased nitrogen isn't much of a concern. Of course (as previously stated), I don't even pretend to be an expert on the subject....

If you're already past the allowable NDL for air (and still within the allowable bottom time for your Nitrox mix), I'd think the above would still apply. Since you're on your way up, and the time on air is only a couple of minutes, then I wouldn't think it would be a real concern.

I generally try to breathe the same gas as my buddy, because it makes dive planning easier. I don't see the point in paying all that money for a Nitrox fill, only to be limited by my buddy's NDL, because he's diving air, and since we're buddies, we've both got to come up when he hits NDL.

 

[TSandM]

The amount of breathing time you get from a Spare Air is so tiny that decompression concerns are not an issue. Not having enough gas to get to the surface, however, is. If you have been deep enough to have a decompression problem, a Spare Air may not even get you to the surface. But the bottom line is that you are better bent than drowned, and far better not to have gone into deco or run out of gas in the first place.

If you are having to buddy breathe, again, your dive is over and you are heading to the surface. The amount of time you will share gas will not raise significant decompression issues, especially as you will be ascending throughout.

It is a good question to ask, though. And to answer your last question, it is better if the divers on the team are on the same gas. But this isn't really for air-sharing reasons, but rather that it gives everybody the same no-deco time, so the person leading the dive doesn't inadvertently take someone else into a decompression obligation.

 

[ZenDiver.3D]

With your basic nitrox course, you are still not training to exceed recreational limits. In fact, increasing your oxygen percentage in EAN decreases safe maximum depths due your absolute depth limits fro higher dose of 02. You will learn all about this in your course.
You also will stay within NDL's of the ean that you are diving. You will not go into deco time or consideration unless you exceed your plan and limits.

In an emergency in this case, breathing off regular air for your ascent should not have any real effect. Check your equipment, maintain it well, and dive your plan and limits, and you should not run into any problems. If you do, your spare air can be filled with up to 40% too if you choose. Just have it oxygen cleaned first.

And if you are planning properly, your buddy and you create your plan together and dive to the most conservative limits if your percentages are different. In that, you will be on the timing.

 

[Sonic04GT]

Thanks alot for the info guys. The only reason I mentioned DECO is the fact that you get a little more bottom time off Nitrox than regular Air which theoretically would possibly put you in Deco while diving Air. Then again that doesn't exactly make sense since I would have been on Nitrox for the entire dive within limits until I had to switch over to air and ascend so disregard that haha

Thanks again. Sounds like I'm good to go. Hopefully never have to worry about it though. :cool2:

 

[Caver95]

Hey Sonic, The spare is there to give you a warm fuzzy feeling(not a tingle in you shoulder). In 17 years of avid diving, I have never fun out of gas, without meaning to, or had an emergency that I felt was life threathing at the time, but you have to pay attention. If your an alert diver, you will have no need for your spare air. My advice would be sell the spare air on ebay, and take some more training with the proceeds.
Good luck.

 

[Sonic04GT]

Hey Sonic, The spare is there to give you a warm fuzzy feeling(not a tingle in you shoulder). In 17 years of avid diving, I have never fun out of gas, without meaning to, or had an emergency that I felt was life threathing at the time, but you have to pay attention. If your an alert diver, you will have no need for your spare air. My advice would be sell the spare air on ebay, and take some more training with the proceeds.
Good luck.

I definitely didn't purchase the Spare Air in fear of running out of air. I purchased it in fear of some sort of equipment malfunction and not being able to get over to my buddy as fast as I'd like to. It never hurts to play it safe. =-P I have no intent on ever using it. I'm usually very alert and have good confidence in my gear but there's no second chances when it comes to drowning hehe

 

[Rick Inman]

In 17 years of avid diving, I have never fun out of gas...

Yes, that would be fun.

I have only seen two true out of gas situations, and in neither would the spare air have helped. In fact, in one event, it was a good thing that the panic-ed OOG diver was tied by a reg and hose to his buddy and not on spare air, which he would have run out of before hitting the surface and most likely have drowned. The fact that he had his buddy's reg locked in his mouth, which kept a helpful person right next to him, probably saved his life.

I am also not a fan of spare air. IMO it creates a false sense of security before a real event, doesn't provide enough gas to relax and handle the real thing, isn't something that promotes practice in actual use, adds a major failure point, and discourages good team skills.

So, whether it has air or nitrox or whatever in it is the least of it's problems.

Just MHO, YMMV.

 

[String]

Woohoo we haven't had a spare air argument on here for ages. I'll check this thread in a few hours to see if its over 300 posts....

 

[JDostal]

Woohoo we haven't had a spare air argument on here for ages. I'll check this thread in a few hours to see if its over 300 posts....

Spare Airs SUCK!

But to answer the question you can safely use a Spare Air filled with Air on a Nitrox dive.