Mask Air Inhale, Deadly?

[RebeliousOatmeal]

A common technique that a lot of freedivers use to lower the "need to breathe" feeling whilst ascending back to the surface is inhaling the air from the mask that you used to equalize while initially descending. It is something that I personally do, and that many others do as well. However, could this technique be something thats a cause for concern?
We all know that we breathe in O2 (oxygen) and exhale CO2 (carbon dioxide), so if the CO2 that we have exhaled into our mask is then inhaled back in on the ascent up, is there a risk that this could increase adverse effects such as light headedness, dizziness, or even black outs?

What do you guys think? How many of you use this technique on your ascent back to the surface?

 

[Porky Pig]

Your thinking is incorrect here. The air we exhale still has oxygen in it. For example, in normal breathing, we inhale air that is about 21% oxygen, and exhale air that is about 15% oxygen.

If you think about the progress of a dive, the oxygen concentration in our lungs will be highest at the start of the dive, and steadily reduce throughout the course of the dive. So, the air we exhale into our mask on the way down will have a higher oxygen concentration that the air in our lungs as we ascend. This means that when we inhale the air in our mask on the way up, we are increasing the oxygen concentration (and, of course, the total quantity of oxygen) in our lungs.

 

[SubSub]

What kind of giant masks are you guys using!? The volume of the air in a freedive/spearo mask can't leave much to "breath in".

 

[RebeliousOatmeal]

I have a couple of low volume freediving masks that are no name, though they look just like the Mako Mini Mask.
Have you ever watched a spearfishing/freediving and wondered as the diver ascends: where the hell are all those bubbles coming from and why are there tons of bubbles just above the mask? Well. this is all the air that you used to exhale into the mask on the way down to equalize it sufficently. Go check out a couple vids and you'll see!

 

[RebeliousOatmeal]

Porky Pig I did not see your response. Thanks for the information!! I just looked it up and its the same concept as giving mouth to mouth resuscitation. Thank you!!

 

[cdavis]

Subsub: its a bit surprising how much air must be used to equalize even a very low volume mask, say 100 cc, small. At 4 atmospheres, thats 300 cc extra you have to use equalizing, almost a third of a liter. Thats a big enough chunk of air to be worth getting back .

 

[SubSub]

Hmm. When you guys put it like that it sounds quite logical. Funny this is something that has bypassed me totally! I'm gonna give it a go sniffing up the extra air.

 

[emile.c]

The French call it the second breath! In my opinion it is OK to do it if you don't pack or, if you pack, at a depth where you can easily breath in. If you force it near surface where your lung have filled up with uncompressed air and are still partially filled with blood due to blood shift it can be a little dangerous for your lungs.
I would say to put it in numbers that it is pretty safe until 8-10 meters (going up).
Emile

 

[3joern]

just yesterday I dive in a lake to 23 m, when I go up, I inhale every 2m a bit of the air that expanse in the Mask (Sphera). Was the first time and I surprised how easy it was, but after I see this topic I remember my instructor told me if I got air in the deep from a can diver then I have also his decomp time.
So, if I start inhale air at 15m (at this point start the expanse for enough air) it has the same decomp effect or not?

 

[emile.c]

just yesterday I dive in a lake to 23 m, when I go up, I inhale every 2m a bit of the air that expanse in the Mask (Sphera). Was the first time and I surprised how easy it was, but after I see this topic I remember my instructor told me if I got air in the deep from a can diver then I have also his decomp time.
So, if I start inhale air at 15m (at this point start the expanse for enough air) it has the same decomp effect or not?

I don't think so. It's the same air you inhaled at the surface. No more. Decompression in Freediving is necessary only when going really deep (like Nitsch did in his 214m. dive) as a precaution.
When you go underwater with tanks the Nitrogen you accumulate is much more because you inhale and exhale many times during the dive.

So it is absolutely safe to breath in the air in the mask.

Emile

 

[3joern]

thanks

 

[SubSub]

I also tried, but find it pretty hard and uncomfortable. I "lock" my throat when diving, and it was a really awkward opening up to inhale through the nose at depth.

I doubt you get much extra time if you're not diving really deep and really push it.

 

[growingupninja]

A common technique that a lot of freedivers use to lower the "need to breathe" feeling whilst ascending back to the surface is inhaling the air from the mask that you used to equalize while initially descending. It is something that I personally do, and that many others do as well. However, could this technique be something thats a cause for concern?
We all know that we breathe in O2 (oxygen) and exhale CO2 (carbon dioxide), so if the CO2 that we have exhaled into our mask is then inhaled back in on the ascent up, is there a risk that this could increase adverse effects such as light headedness, dizziness, or even black outs?

What do you guys think? How many of you use this technique on your ascent back to the surface?

It's perfectly safe and for extremely deep dives, the mask is free air. I put a lot of air in my mask when I do my mouthfill. On the way up it's there when I need it and for CNF I actually can feel that O2 landing when I sniff most of it back in around 25M.