Freedive/SCUBA (specialist) skip breathing at depth

[growingupninja]

I have a work gig coming up and thought I would throw this out there to see if any freediver with relevant experience would be able to shed a little light beyond what I know from experience and research...

Doing a shoot at 30m, looks like crew on scuba. I am very comfy CWT hunting aspetto at those depths and have a 6:44 comp static, but will probably be expected to hit an off camera octo as needed. I haven't done a single tank breath since getting padi cert over 20 years ago... I am very familiar with Boyle's law and it's implications, DCS in a pure freediving context, and will not be changing elevation, it is professional shoot with safeties (likely scuba only) but I am basically going to be skip breathing/doing a series of holds at depth, which as you know in recreational scuba is considered a big no-no.

If I am taking full lung breathes at 3atm then I would need to keep an eye on CO2 build-up, correct, since lung O2 is going to be so very much higher than at surface and at my level of training ventilatory drive is linked more to low O2 as opposed to elevated CO2?

Ordinarily dive response and (my) slow ascent speed seems to keep me from DCS harm when doing serial deep cwt dives. For this if I treat the dive as more a scuba thing using scuba tables (scrub on a tank at 20') i would be covered, ya think? It seems skip breathing and/or half lung breathes at depth would lead to reduced nitrogen buildup although i may be running higher than normal CO2... Obviously they will have safeties and protocols but they are usually coming at it from a pure scuba perspective. Curious to hear from strong freedivers who perhaps also scuba.

Thanks

 

[cdavis]

Skip breathing at 30 m will probably give you a nasty Co2 headache, but if you treat the whole thing as a scuba dive,using scuba tables, it should work, safely. Treating it like a scuba dive includes a scuba ascent rate. Come up like a normal freedive and you would be courting a DCS hit.

 

[growingupninja]

Okay, thanks for the response, Connor. The higher total O2 thing/vs CO2 thing will be interesting. I will probably run some extended dry one breath holds and see where I land. Right now my CO2 tolerance is as high as it has ever been so i haven't been able to induce a headache with any sort of static tables, only dynamic work.

 

[japppo]

This might be obvious to everyone but I'm just saying out loud. As you mentioned Boyle's law, remember to exhale continuously during any ascent if you have filled your lungs at depth with pressurized air.

By experience I know that exhaling during the ascent does not come naturally for a freediver... Maybe ascend with scuba and breath continuously, which you were planning to do anyway?

Someone might get the idea to use a spare air bottle during spearfishing for example. I would not recommend that unless for an emergency, and even then proper training would be necessary.

Inhaling pressurized air could save your life if you get stuck in the bottom for some reason, but it can as well burst your lungs and kill you during the ascent if not exhaling continuously.

 

[growingupninja]

This might be obvious to everyone but I'm just saying out loud. As you mentioned Boyle's law, remember to exhale continuously during any ascent if you have filled your lungs at depth with pressurized air.

By experience I know that exhaling during the ascent does not come naturally for a freediver... Maybe ascend with scuba and breath continuously, which you were planning to do anyway?

Someone might get the idea to use a spare air bottle during spearfishing for example. I would not recommend that unless for an emergency, and even then proper training would be necessary.

Inhaling pressurized air could save your life if you get stuck in the bottom for some reason, but it can as well burst your lungs and kill you during the ascent if not exhaling continuously.

Yes, thank you, i remember the free ascent protocols from scuba but would not intend to do anything like that and would probably be stopped by safety divers! I am sure their dive team has a protocol but my own thought after breathing any gas at depth would be to ascend up the line with a breathing tank at a slower than scuba rate (my deep freedive rate is slow compared to most freedivers but obviously faster than scuba rate), take the last 15m even slower and probably scrub for a good while at 20' since CO2 levels could be quite high after doing holds with way high O2 concentrations... and there is some speculation that DCS symptoms among freedivers may be related to CO2 as much as nitrogen.

It is a pro shoot so the layers of safety are actually way over anything I am accustomed to in the context of what I am usually up to in the ocean...

 

[cdavis]

This is a bit above my pay grade, but C02 contributes to narcosis (I think). I've read that the contribution is substantial during very deep dives. Nitrogen narcosis at 30 meters is present but not too much of a problem. What if you add a substantial cnc of c02?

 

[growingupninja]

I am not sure what the narcotic effect of CO2 would be at depth but high levels at surface definitely effect coordination and judgement. I run really high levels in training and when spearing shallow, especially lobster diving where surface interval is just a few breaths.

 

[growingupninja]

Shoot went well, everyone safe. When the client releases the images (it was the gig of a lifetime) in a couple weeks I will post dive/freedive details to anyone interested. Breathed 30% nitrox, 3/4 to 1/4 lung holds on the bottom, not for too long (maybe around a minute at a time?). Bottom time around 20 mins. Did 5-7 min safety stops at 6M on 50% O2. Didn't push the holds whatsoever since the gig wasn't about me holding my breath and there were gnarly environmental concerns and I was mask-less during the holds, but once I got more relaxed with everything it was okay. And of course safety divers were rock solid. Still don't dig the regulator in my mouth and being strapped to a tank forget it but hitting nitrox at depth, dumping the reg, then going to work was pretty cool.