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FRC Diving

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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New Member
Jan 16, 2002
So how is everyone doing with the FRC dives? I hit 54' Saturday and it felt like 150'. I must admit the surface dive feels really smooth though. Anyone else?
Well, I do them only for the training and I think I get different volume of air almost every time... I guess it takes time to be precise.

I hit 22m last weekend and this saturday I hit 28m. (Don't know if the difference was the amount of air I had in my lungs.)

My lungs has never felt that empty ...

I will take it real easy and slow with this training.

I dont understand how you guys equalise

I tried some frc dives from the defintion Eric described (Leaving at the bottom of a normal breath) and I struggled to equalise at about 5m because of the volume I start with. I use the the standard equalising method ie pinch and blow.

What secrets are you using to dive 28m with such little air volume :confused:

equalizing on an FRC dive

I have been doing FRC dives in a 10' pool, which means that once I exhale completely, I have to reverse pack a couple of times to empty out even my residual reserves, to feel any negative pressure. The only way to equalize then is to reverse pack some air back in the mouth and trap it there by closing the epiglotis.
Equalizing seems like it would be hard, but maybe you need to fill everything above your epiglottis (mouth, nasal, and upper throat) to aid in equalization, even though your lungs are not full. You should be able to separate the lungs from above the epiglottis into two distinct air cavities. It’s the volume in the lungs that defines FRC and its advantages, not what’s above the epiglottis. I’m just guessing here!

Another question I have for Eric F., that I have had ever since he discussed it on an earlier thread, is the importance of the breathup. Eric, I believe you stated that the breathup is not as important for FRC diving as it usually is. It would seem to me, that since the lungs put oxygen into the blood stream and remove CO2 from it, that the breathup would be even more important. This is because the lungs are not going to have much air in them to pull oxygen out during the dive. The breathup seems like it would be the only time to enrich the blood and tissue with oxygen? Am I totally off here?

Maybe its in my mind, but it definitely seems easier when doing negative statics to do a good breathup and really get some air volume in and out of the lungs before doing the final exhale.
The trick to equalising is to use Eric's mouthfill technique at the surface, before you dive. If you do it properly, you will have enough air to get to 20+ metres. Reverse packing is much less efficient.
Erik Y.
I did an FRC dive to 18 metres a few weeks ago, with a 15 seconf static at the bottom.
Last weekend when diving with JMD I did an empty lung (1 reverse pack then one more to fill my mouth) to 10 metres and 2 minutes! That's a PB for me :)
Erik Y.
I fill my mouth at about 5-10m and equalize with my tongue (frenzel) the rest of the way down.

I belive I start with about 3.5l of air (some 1/2 l under half lungs; Residual volume + Expiratoric reserve volume). It could be 3 or 4.5 liters, as I said I get different amount of air every time because I have not trained to do this type of diving.

This should leave about 0.9-1.1 liters in my lungs at 28m which should be compared to the volume at the depths I 'm diving to with full lungs.

50m and 8liters gives ~1.3liters left. Equalizing is normally no problem for me with full lung diving to 50m.

So I don't find it strange..:duh
Last weekend, I managed to reach 32.3m on a single mouthfill from the surface.

On an FRC dive, I can fill my mouth inverted at 10m, which would take me to 74m, still equalizing with air from the one mouthfill.

If I flare horizontally on an FRC dive, I can fill my mouth deeper, at 13-15m, which would put me as far as 95m, still without resorting to water equalizing techniques.

The reason I can fill my mouth so deep is that I become 'gorged with blood' after a few warm up dives and my residual volume decreases dramatically. Also, I lose the ability to inhale a full breath. When I can no longer inhale a full breath, I know I'm in the zone.

Obviously you need to be very good at the mouthfill in order to air equalize on FRC dives.

Eric Fattah
BC, Canada

I can reach 18-20m on one mouthfill at the surface.:hmm

How deep have you tried on FRC, Eric?
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So far, I've done several repeats to 31m on FRC (mouthfill at 8-10m) Feels great. Not running out of air at all. I hope to progress to 40-45m on FRC within the next month. Takes time, but the feeling is worth the slow progression.

Vancouver, BC
what kind of suit configuration were you all wearing for those dives? were you sinking all the way from the surface?
So far I have tried three suit configurations for FRC dives:

1. No suit, no weight
Sink at RV.
Must do one monofin kick to start sinking at FRC
Terminal velocity 0.85m/s.
Ascent from 40m takes 22-24 monofin strokes.

2. 3mm/5mm (bottom/top) Elios w/10lb belt
Sink at RV, but must do one or two monofin kicks to sink at FRC
Terminal velocity 1.00m/s.

3. 5mm Elios w/19lb belt
Sink at FRC.
Terminal velocity 1.35m/s, even while pinching my nose.
Ascent from 40m takes more than 40 monofin strokes.

Eric Fattah
BC, Canada
Now that you have stopped all other exercise except FRC diving, what kind of physical transformations is your body undergoing? Have you put on any subcutaneous fat due to no suit, or have you atrophied or even increased muscle density? Specificity of exercise often yields interesting adaptations.
So far, my ERV has increased from 3.25L to 4L. My VC has decreased, especially after a diving session. My VC with packing has decreased dramatically. My legs seem to have more 'jump' and anaerobic power. My arms and legs are extremely weak for the rest of the day, after diving. I also lose a HUGE amount of water via immersion diuresis. For example, I often weigh in at 176lbs in the morning, and come home from diving weighing 168lbs, despite drinking tons of water.

Eric Fattah
BC, Canada

Eric now I understand how you guys are equalizing on air. But how do you dive to 32m with only a mouthfull of air :duh My mouth sure as heck wouldnt hold enough air to equalize my sinuses to that deep ??


ps What is your ERV mean
The volumes/capacities of the lung

I hope this will clear something for you Ivan!

RV=Residual volume, The minimum inner volume for the lung.

ERV=Expiratoric reserve volume (The air volume you can exhale from FRC(=Functional residual capacity))

TV=Tidal volume (the volume of air used for each breath in normal breathing)

IRV=Inspiratoric reserve volume (The air you can inhale from FRC+TV)

FRC=RV+ERV, Functional residual capacity

VC= ERV+TV+IRV, Vital capacity (The volume of air you can exhale on a full lung)

TLC=RV+ERV+TV+IRV, Total lung capacity

Correct me if I'm wrong.
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Thank you Peter I understand it better now, I never knew their were so many abbreviations.

Degrees of FRC

The theory behind FRC seems sound but I still dont feel tempted to go that route because:
1) I have never come accross water warm enough that I could dive for more than 30 minutes without getting cold,
2) My recreational depths and times on full lungs are good enough for my purposes, and If I understand the FRC theory, it wouldnt give me longer bottom times anyway.
3) I dont have N or CO2 toxicity issues on even my deepest dives
4) I'm fearfull of a sub 15m blackout whilst recreational diving.

I'm just wondering if I'm misunderstanding something and if I could be convinced otherwise.

Also, if FRC is the way to go, could it then be implied that full lung diving without packing is preferable to full lung with packing. As I understand it, the long term benifits of FRC diving(increased haematocrit) come from the fact that one is diving constanly hypoxic. A full lung dive is hardly hypoxic, yet it is a degree of the same thing is is not? And infact all the benifits of FRC diving should also be evident, but to a much lesser degree of course in full lungs minus packing. If my reasoning is correct, how come most FRC divers used to prefere packing over not packing on full lung dives.

Personally I like the idea of minimising changes in bouyancy and expending minimal efford in the early stages of the dive. I plan to go back to diving without packing for a while and see how it goes. Also,I dont want to be doubting FRC diving because I dont understand it properly, so If any of you FRC divers out there have got the time to try convince us fence-sitters we're missing something, we're all ears:) cheers
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