• Welcome to the DeeperBlue.com Forums, the largest online community dedicated to Freediving, Scuba Diving and Spearfishing. To gain full access to the DeeperBlue.com Forums you must register for a free account. As a registered member you will be able to:

    • Join over 44,280+ fellow diving enthusiasts from around the world on this forum
    • Participate in and browse from over 516,210+ posts.
    • Communicate privately with other divers from around the world.
    • Post your own photos or view from 7,441+ user submitted images.
    • All this and much more...

    You can gain access to all this absolutely free when you register for an account, so sign up today!

A Few Thoughts on Tech Freediving

Thread Status: Hello , There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.


Deeper Blue Hypoxyphiliac
Oct 24, 2002
Howdy all, trust everyone had a merry christmas/happy hanukah? Good to hear :)

Been doing some thinking over the holidays about 'tech' freediving. From my understanding, we can't do depth dives on highly oxygenated air because of gas exchange and oxygen toxicity, right? What about doing empty lung dives on 100% O2? Again from my very limited understanding, there's a cessation of gas exchange once the lungs start to compress, so if we did a negative on pure ox, would we be as susceptible to oxygen toxicity? Even if there's only a marginal increase in safety, then we would still be able to do dives on say Ntirox-40 or something?

I've got a little more to say on this, but I'll wait for a few replies first... thanks for your input :)
hi Loopy

Maybe this is a stupid question but even if you have 100% 02 on a empty lung dive I would have thought that you still need air in your lungs to equalise your ears. Maybe I dont know how to do empty lung dives properly, but I blow all air out then attempt to equalise with no air. I cant go past about 2m.


Not advisable.


Still in dangerous territory with the 02 toxicity (although slightly less so), but now you would be putting an immense strain on your lungs as they gobble up the 02 and force your lungs into a massive (probably dangerous) blood shift.

Don't do it - especially is you can clear your ears well i.e. via the mouthfill technique!

It'll end in... :waterwork
Yeah, the reason I ask is not because it's something I was gunna try, but just something I thought of. At the mo, Seb Murat is doing 100m negative dives (yup, 100m in constant weight on empty lungs!). He's using wet equalisation, so basically he doesn't really have to equalise. Obviously you have to be a superhuman to try this kinda stuff, but I just got to thinking that if he's doing 100m constant on 21% O2, and there's no gas exchange, he should be able to do insane stuff on pure 02.

Ivan - my deepest negative was only 5m, but if you fill your mouth with air, then close of your throat, you should be able to equalise using just the air in your mouth. That should take you down a fair ways. I find I need at least about 2.5m of depth to do an effective negative anyways.

Yeah I cant do that mouthfill thing, I ll just stick to full lungs.

Where did you get this idea that there is no gas exchange?

There is always gas exchange in lung tissue until total collapse of all alveoli?

Seb may be getting close to that point if he is doing that kind of depth and starting with empty lungs.

100m constant with full lungs, yes. but 100m constant weight with empty lungs?? :hmm
where did you get this information? sorry, but this sounds extremely unlikely to me. could you have misinterpreted something you heard or read?
Heard it from the man himself... :D

I'd love to forward off the email to everyone interested, but it'll be a couple of months, because it's on my other comp back in Canberra, and I'm stuck here for 8 weeks :duh. His technique is absolutely insane - Ben and Alun, pm me with your email and once I get a new address here I'll mail you the gist of the idea.

Ben, the no gas exchange thing was something I read, I think it may have been on another post... have you got any examples of collapsed alveoli? That's sounding rather nasty... :(
  • Like
Reactions: Alun
sorry to sound so sceptical, but i still don't believe this.

don't get me wrong, i'm not trying to suggest that you're telling porkies or anything. (sorry- cockney... 'pork pies, lies'... never mind). :eek:

the fact that you got this information from an email rather than from a personal conversation tells me that misinterpretation is much more likely. he may even have been pulling your leg? :t

there are 3 major problems with this dive:
1. equalising the pressure in the ears
2. equalising the pressure in the lungs
3. being able to store enough O2 to complete the dive

i could envisage that it may be possible to overcome the first problem with wet equalisation. but as for the second two....

if he begins the dive with a typical residual volume of 1.5litres. then at 100m his lungs should have a volume of 136ml!!.... this must surely be less than the volume of the trachea!.... so i wonder how on earth could possibly equalise this pressure without sustaining massive lung damage?

exhaling before a dive means that he will store at best 50-60% of his normal O2 capacity (i think those figures are about right). a 100m CW dive probably takes the best part of 4mins...... i really dont know what else to say?!

what's your view on this EricF? any thoughts?

Although I don't have any real data on the volume of incompressible spaces in the lungs, the sums Alun gave seem very sensible to me.

I really can't believe it is possible, unless the lungs are flooded with some extra surfactant to reduce air space - very nasty.

The O2 storage problem is also mystifying, but could be explained by the massive blood shift that would result from diving with a small breath. This would effectively cut blood supply to the muscles so that the dive may be completed without musclular perfusion.


Loopy are you serious 100m no air. I dont hink most people including E fattah can go much over 20m. How is seb doing it. I remember Eric F telling us that Seb had done 105m constant weight in training but I dont remember him saying empty lungs.

I think Eric already made some comments on this type of topic some months ago.

As far as I remember he said that seals avoid the gas toxicity problems that we face as they dive without air in their lungs. He also mentioned that this should be possible for a human with good enough blood.

It should actually be a more efficient way to dive as you also reduce boyancy problems and carry less weight.

Perhaps the only really limiting factor is lung damage. On this subject, doesn't the air in a no-limits diver at 170m reach a tiny volume? Is it so much more impossible to dive with empty lungs to 100m?


limiting factors.... let's not forget the halved O2 storage either!

a freedivers with 10litre at the surface should a lung volume of 0.555litres at 170m

a freediver leaving the surface with 1.5litres will have 0.136litres at 100m.... that's about one third of a coke can!

to have a lung volume of 0.136liters starting from 10litres at the surface, you'd have to dive to about 730m!!

the difference doesnt sound much, but relatively speaking that is a very significant difference in volume.

Loopy forwarded me Seb Murat's e-mails. He does say that he's working towards a 100m empty lung constant ballast dive, and that he's trying to simulate it in the pool, but he doesn't really mention if he has managed it in constant weight -- I did think he said he managed it on the sled.

I feel somewhat proud because around a year ago I suggested to Sub Murat the idea of doing a 700m no-limits empty lung dive to go dive a new underwater city they think might be atlantis (near cuba). The idea was to minimize the risk of DCS, O2 toxicity, narcosis, etc... However, the dive would take 8-9 minutes on the sled, meaning you'd need to do an 8-9 minute exhale static. It seems he took this discussion and applied it to his current training.

However, I also theorized about a 100m constant weight dive, especially after the terrible narcosis problems I was having down there (and Seb told me that he too had really bad narcosis down there). So, maybe this was his solution.

He did say that he 'passively' exhales, i.e. not a forceful exhale, so he still has a significant volume of air in the lungs, but he can still sink the entire way down to the bottom.

People ask, is 100m on a semi-exhale possible? The answer is certainly yes, but conditions need to be perfect. The dive will take about 2'50 to 3'30, so at the very minimum you need to do a 2'50 - 3'30 passive exhale static.

Then, the ascent must be 95% anaerobic (except for myoglobin), and done purely on stored ATP/CP/myoglobin-O2/ and glycolysis. The blood shift would be so strong that almost no blood would be in the legs. The problem I foresee is that even in an elite athlete, there may not be enough stored energy in the legs to sprint up from 100m. If not, the legs will fail around 50-15m, and there would be no time to stop and rest due to the low O2 store. So, you need to make it to the surface in one immense, uninterrupted sprint.

Of course, the dive would have to be done with no suit, just as Seb Murat dives, because this is the only way you can sink all the way down with minimal buoyancy change.

In fact, when diving in a no-suit environment, it is not at all obvious that inhaling would result in a deeper depth than exhaling, if the above conditions can be met.

Of course, it takes years of flexing your ribcage to be able to reach the 'solid lung' state that you reach at 100m on a passive exhale.

They say that in seals (who exhale), gas exchange stops at 50m. Dolphins, who inhale, but have huge sinus cavities, experience a cessation of gas exchange at 70m.

So, in Seb's case, if he experiences a cessation of gas exchange at 70m, he's safe from O2 toxicity, CO2 narcosis, DCS, and the works.

Eric Fattah
BC, Canada

Very interesting Eric, it seems pretty dangerous as you said that if your legs fail you cant wait cos of no o2 as far as im concerned you guys diving to depths where all this dangerous sh%# happens are crazy I think i will stick to statics and 20m depth where everything is fairly safe. Oh can Seb do exhale statics for 3:30.

so the empty lung constant weight dive to 100m becomes a NL dive to 100m with a passive exhalation.... i find this a little more believable. i do believe that it's possible to store enough O2 to complete an NL dive to 100m, something that could take as little as 2mins.

i just looked up the value of the dead air space and it's about 150ml.... less than i thought. if the blood shift can reduce the lung volume down to 150ml, then lung equalisation shouldn't be a problem. there is obviously a limit to blood shift volume - ie. it can't reduce your lung volume to zero!:duh the question is whether it can reduce it to 150ml.... who knows?

for a passive exhalation dive to 100m
2.5litres... 0.227litres (> 150ml) possible?? depends on maximum blood shift.

for an empty lung dive to 100m
1.5litres... 0.136litres (< 150ml) extremely unlikely

Eric, can you forward me his email(s?) please. i'm interested to see what he says about it all. i'll PM you my address.

I had a look back at some of Eric's posts and he does mention the actual lungs 'filling' with plasma.

If this happens wouldn't it help to protect the lungs and require a recalc on your volume figures Alun?


P.S. you can spray foam into car tyres to mend punctures, maintain pressure and prevent collapse. I wonder how toxic it is.... :D
Ahh, the joys of monday morning DB... :D

Have you got that email yet Alun? There's actually 2... I think I sent both to Eric, but if you don't get them, let me know, I'll see if Wal still has them. It all came about because a mate mentioned that he heard Seb did 100m dynamic constant. I emailed Seb and asked him, and he said nah it was dynamic. I'll PM you my email, let me know what you need :)
Gas exchange only stops because of total alveolar collapse - but by the sound of things, that is near happeneing in Seb's dives.

I like the idea of near-empty lung diving in this way - but water equalisation would put me off somewhat!
nope, not seen them yet...

the 'lungs filling with plasma' thing... i've read this before somewhere, and i'm not convinced if there is any truth in it. it may be one of those freediving myths. what do you think Dr. Ben?

DeeperBlue.com - The Worlds Largest Community Dedicated To Freediving, Scuba Diving and Spearfishing


ISSN 1469-865X | Copyright © 1996 - 2024 deeperblue.net limited.

DeeperBlue.com is the World's Largest Community dedicated to Freediving, Scuba Diving, Ocean Advocacy and Diving Travel.

We've been dedicated to bringing you the freshest news, features and discussions from around the underwater world since 1996.