CESA Training

[David Novo]

From 40 m, a safe ascent would take 4 minutes. Let's take 5. My SAC in normal conditions is between 9 (fit) and 15 (tired) l/min. In a very stressful situation, even though I am cold as ice in stress , people told me that I should triple my SAC. Let's take 45. From 40 meters, let's be very conservative again. If I consider, for the sake of the science that I stay 1 minute at 40 meters, 1 minute at 30, 20, 10 and 2 minutes (to make it 5 minutes) between 10 and surface.I would consume 45*(5+4+3 +*2*2)= 720l. I would need a 3,6 liters pony. let's say 4 as you mentioned. What's the volume of a SpareAir? Anyway, I would need a pony that I can travel with meaning empty and take it apart before flight check in and fill it up the destination dive shop.

@Dody you need c. 4L at 200 bar, assuming:
- SAC of 30 L/min (twice, not three times the base one you considered)
- 9 min from 40 m to surface (1 to solve things in the bottom, 4 to get to the safety stop, 3 at the safety stop and 1 to the surface).

I am sure it does not look as conservative as when you wrote it.

 

[Dody]

Ascending from 40m, you have an average pressure of 3 bar, so a SAC of 15L/min leads to an actual consumption of 45L/min.

The OP consciously or not considered a SAC of 15L/min.

P.S.: I am aware that it can be lower with a safety stop but the error is on the conservative side.

Ascending from 40m, you have an average pressure of 3 bar, so a SAC of 15L/min leads to an actual consumption of 45L/min.

The OP consciously or not considered a SAC of 15L/min.

P.S.: I am aware that it can be lower with a safety stop but the error is on the conservative side.

If you look at my calculation, I used a SAC of 45l/ min and I took the depth (pressure into account). That’s why I multiplied by 5+4+3+2+2 considering one minute at 40, 30, 20 and 2 minutes at 10 meters.

 

[Dody]

@Dody you need c. 4L at 200 bar, assuming:
- SAC of 30 L/min (twice, not three times the base one you considered)
- 9 min from 40 m to surface (1 to solve things in the bottom, 4 to get to the safety stop, 3 at the safety stop and 1 to the surface).

I am sure it does not look as conservative as when you wrote it.

Yes, it is even less than 4 liters.

 

[David Novo]

If you look at my calculation, I used a SAC of 45l/ min and I took the depth (pressure into account). That’s why I multiplied by 5+4+3+2+2 considering one minute at 40, 30, 20 and 2 minutes at 10 meters.

Oh, I see. I stand corrected.
However, you are considering a fast ascent 10m/min with no safety stop.

 

[David Novo]

Yes, it is even less than 4 liters.

The difference should not be significant and would result from the average depth you consider.

With 3 bar for simplicity on the conservative side, it is 4.05L.

 

[Edward3c]

Your can’t over estimate the gas used under stress. I’ve done a 20m dive and drained the tank in 11min, a consumption rate of 45Lt/min. I knew I was breathing hard, but I was surprised at how quickly the gas went down. I normally have a SAC of 13Lt/min in U.K. waters.

 

[Gareth J]

Interesting that we have moved from CESA to "is there enough gas in the pony?".

CESA - a direct ascent to the surface on one / no breath.
Pony (or similar) - Redundant gas reserve, in excess of 600 litres.

On the point of increased breathing rates. When i did my CCR mixed gas training, one of the discussions was about increased breathing rates under stress. DERA did a study on Navy divers, they found that breathing rates increased beyond three times when divers where stressed during an emergency (forced equipment failure). The raised breathing rate dropped when the diver reached their perceived first point of safety. This varied from diver to diver, as a general rule, they found the first or second stop was perceived as a point of safety.

 

[halocline]

Would it be considered safe to practise CESA training from 10 then 20 and eventually 30 meters?

I'm going to apologize in advance for not reading the 12 pages of this thread, and it's possible that I'm just repeating something already said. Sorry!

I would not practice a CESA from 30 meters to the surface because it's really hard on your body, and there is a DCI risk. It is an emergency procedure. I understand you want to be prepared for all possibilities. You could try, instead, doing a 30 meter CESA from shallow depths, maybe 5 meters, just at an angle so you are actually swimming 30 meters while exhaling. That might give you the same practice benefit with far less risk of baro trauma or DCI.

If you dive correctly (and your buddy does too) you will never need to rush to the surface, unless you're being chased by a sea monster!

 

[dmaziuk]

I would not practice a CESA from 30 meters to the surface because it's really hard on your body, and there is a DCI risk.

I wouldn't practice CESA from 30 m because urge to breathe is controlled by CO2 build-up, you won't be venting enough CO2 on the way up to prevent it, and in the time it takes to do 30 m at safe ascent rate, it's going to build up enough to make the experience really suck. So if I really wanted to do that, I'd first get enough freediving training to comfortably hold my breath for a couple of minutes.

 

[halocline]

I wouldn't practice CESA from 30 m because urge to breathe is controlled by CO2 build-up, you won't be venting enough CO2 on the way up to prevent it, and in the time it takes to do 30 m at safe ascent rate, it's going to build up enough to make the experience really suck. So if I really wanted to do that, I'd first get enough freediving training to comfortably hold my breath for a couple of minutes.

That's a really good point about the CO2 build up.