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I know we shouldn't be fishing on CCR but...

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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greendiver

Sea fanatic
May 2, 2005
482
59
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Hi guys,
As some of you might know I am into spearfishing for a while now.
I am also a Scuba diver and lately I am diving on Closed circuit.
(that means no bubbles, no noise..almost unlimited air and depth)

I WOULD NEVER EVER USE THIS UNIT TO GO FISHING..however..
Doing an espeto at 60 meters for 2 minutes...woowww...
You wouldn't believe what will move in front of you...
I will soon post some pictures, because making pictures is not forbidden ;-)
 
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I would not go any deeper on air them 60 m if i was you cuz of the PP (particle pressure)

O2 becomes toxic
 
Correct me if i am wrong but as i understood it re-breathers monitor the pressure of oxygen in the air you breathe and adjust it according to depth? i recently went to a lecture by a guy, whos name i have forgotten, about diving to 160m and doing wreck penetrations, in the water for 8 hours at a time because of deco stops.
Greg.
 
yeah rebreathers are used for far deeper than 60m but there are rumours of umberto pelizzari spearfishing at 90m so go for it!!! (freediving)
 
I'm absolutely not an expert on rebreathers so this may be cobblers but here goes.

I think old fashion rebreathers like WWII ones had a bottle of oxygen, an inflatable bag and a filter containing soda lime. They were closed syatems and you breathed the oxyen over and over again from the bag while the filter removed the CO2. As your body used the O2 you manually squirted some more from the bottle into the bag. The bag acted as a regulator as being flexible the pressure of oxy you breathed was the same as the pressure of water at the depth you were at, as the water pressed on the outside of the bag.

Early underwater explorers such as Hass and Cousteau found that as you passed 40 foot the pressure of oxygen you breathed started to poison you. Cousteau quickly turned his interest away from rebreathers and this led to the invention of the aqualung. Hass in particular perserviered and used rebreathers for filming and spearing (although he was also a great freediving spearo as well).

Modern rebreathers are different. Although they still basically use the same principle you have a computer controlled management system, you don't use pure oxygen and the system is only semi closed.

Instead of oxygen modern rebreathers use Nitrox or oxygen enriched air. Nitrox is made by adding compressed oxy to compressed air. It is usually known by a number eg Nitrox 32. This is a gas where 32% is oxygen and the rest mostly nitrogen. Air is Nitrox 20 - got that?

As you dive deeper on air the partial pressure of the 20% oxygen contained in the air starts to become toxic. Hence one reason for the max depth rating of air. Nitrox has a lower max depth before the extra oxygen climbs past the recommended partial pressure. Different Nitrox numbers have different max depths. Higher number shallower max depth.

Modern rebreathers don't have to use Nitrox or even air but can use a range of gasses just as scuba does.

So this is like the briefest of explanations and it is a complex subject but hope this helps.

Dave.
 
jimy286 said:
I would not go any deeper on air them 60 m if i was you cuz of the PP (particle pressure)

O2 becomes toxic
Click to expand...

Hey jimy,
On CCR you have a set PPo2 setpoint, in my case PPO2 of 1.3, it keeps your PPO2 (read partial pressure), at the same level all the time.
60 meters on air is not advisable, however not a problem, PPo2 is still fine.
greets..
 

Hey Dave!!
Long time no see!
Yeps, something like that..
If you make deeper dives you just lower the O2 percentage, to 16% or so and at 70 meters you still will have an acceptable PPO2.
and if you go deeper you can lower the O2 percenatge again..
Now...all of us here..will directly understand what would happen if you go up with not enough percentage of O2 in your loop....hypoxia..some kind of SWB..:duh
 
PP = Partial Pressure: a mixture of gases, each gas has a partial pressure which is the hypothetical pressure of that gas if it alone occupied the volume of the mixture at the same temperature. The total pressure of an ideal gas mixture is the sum of the partial pressures of each individual gas in the mixture.
 
I used to dive pure O2 and Basic Mixed Gas. Have not for a long time. I have used the Emerson which was a modified Laru rig. Mk 15 mixed gas and Draeger rig. Sodasorb was the scrubber I used in my rigs.
 
The Emerson rig was prone to leakage mixing with sodasorb and creating a caustic cocktail. In my time we had to get a O2 toxicity test in a recompression chamber to see when o2 became toxic. That depth limit is different for different people Just like fingerprints.
 
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