???Future of Open Circuit Mixed Gas and Rebreather Diving???

[ahereng]

After getting my ccr eight years ago I have done a LOT more diving in the 50-65m range. These dives were just not worth it on OC(especially with current helium-prices), but is easily affordable on a ccr.
So don't just use current dive-patterns for the "calculation"..

 

[Celt]

After getting my ccr eight years ago I have done a LOT more diving in the 50-65m range. These dives were just not worth it on OC(especially with current helium-prices), but is easily affordable on a ccr.
So don't just use current dive-patterns for the "calculation"..

What people are doing at those depths now is using less helium not buying rebreathers
Edit: or none

 

[Tribal]

HeliAir, you’re only adding helium after 57m PPO2 of 1.4 very simple and little helium.

If I can only afford a race car but I can’t afford the right tires to ride on the track, I’ll be smart and don’t race that day.

 

[Wibble]

HeliAir, you’re only adding helium after 57m PPO2 of 1.4 very simple and little helium.

You appear to have a massively greater tolerance for narcosis than most people. I -- and many others -- consider helium as a requirement for dives beyond ~35m/115ft. Beyond 40m/130ft helium is essential; doing 45m/150ft plus on nitrox is something I did years ago but not something I'll do now.

Narcosis is completely avoidable on CCR; just add a little helium to the mix. As posted earlier, CCR gently sips helium and it becomes affordable. Even buying a spare trimix 3 litre cylinder would cost less than an OC helium fill.

For deeper dives, narcosis is just plain dangerous as you nee your wits about you. Not least when narked, you don't remember much of the dive; just becomes a "went down, mooched around, came up" dive.

Also: could you clarify your definition of heliair please.

My understanding is heliair is 10/50: fill to 110bar of helium and top off with air from the compressor. Benefit is it's really simple to mix and doesn't require O2 clean equipment. Drawback is it's hypoxic and has a low PPO2 for 60m through 110m (0.7 to 1.2), but still not enough helium to clear your narcosis or have a low enough gas density. 10/50 slightly makes sense on a rebreather because it will add oxygen to increase the PPO2, but is still too hypoxic in the shallows, so requires an alert diver.

 

[Celt]

You appear to have a massively greater tolerance for narcosis than most people. I -- and many others -- consider helium as a requirement for dives beyond ~35m/115ft. Beyond 40m/130ft helium is essential; doing 45m/150ft plus on nitrox is something I did years ago but not something I'll do now.

Narcosis is completely avoidable on CCR; just add a little helium to the mix. As posted earlier, CCR gently sips helium and it becomes affordable. Even buying a spare trimix 3 litre cylinder would cost less than an OC helium fill.

For deeper dives, narcosis is just plain dangerous as you nee your wits about you. Not least when narked, you don't remember much of the dive; just becomes a "went down, mooched around, came up" dive.

Also: could you clarify your definition of heliair please.

My understanding is heliair is 10/50: fill to 110bar of helium and top off with air from the compressor. Benefit is it's really simple to mix and doesn't require O2 clean equipment. Drawback is it's hypoxic and has a low PPO2 for 60m through 110m (0.7 to 1.2), but still not enough helium to clear your narcosis or have a low enough gas density. 10/50 slightly makes sense on a rebreather because it will add oxygen to increase the PPO2, but is still too hypoxic in the shallows, so requires an alert diver.

Just saying there’s more than 1 way to skin a cat, people should look at all the options.

 

[Celt]

If I can only afford a race car but I can’t afford the right tires to ride on the track, I’ll be smart and don’t race that day.

But some will just use the Volkswagen

 

[Celt]

Also: could you clarify your definition of heliair please

That would depend on the user, for a diver who is happy enough on air at 50m would only need to use helium to maintain the PPO2 of 1.25 max depth ie. 18% O2 at 60m. You only have to test for O2. He could drop it a little more if wanted to keep the nitrogen partial pressure down.

 

[Wibble]

Just saying there’s more than 1 way to skin a cat, people should look at all the options.

Absolutely.

I can use helium and have access to it. With the rebreather, I will use very little so it makes financial sense to dive the right gas for the dive.

OC is out of the question for mainly deep diving. Just for a moment say helium cost nothing. Open Circuit deep diving is still a logistical nightmare as you need access to a compressor, booster and large volumes of helium and oxygen every night. A week's diving in Malin would need an entire 'J' cylinder*** for each diver, e.g. a whole one for helium and another one for oxygen. A boat load of 10 OC divers needing the best part of 20 'J' cylinders.

For CCR one J would last weeks as the volumes of both helium and oxygen are so low.


*** A 6ft/1m85 high 50 litre J cylinder at 200 bar contains 10,000 litres of helium (ignoring that you can't scavenge the last dregs of the cylinder). With a twinset containing 5,280 litres (2x12 at 220 bar), 45% of which is 2,376 litres of helium. For a laugh (although the gas monkey won't be laughing), call that 4 fills (as there'll be some residual gas in the twinsets). Thus one J feeds one diver for 4 or 5 days. Ten divers means ten J's.

And then there's oxygen. 50% and 80% for the deco gasses... Oxygen's getting expensive too.

Weekly deliveries of circa 20 J cylinders of gas to run a single Open Circuit dive boat!

 

[Tribal]

But some will just use the Volkswagen

And there is nothing wrong with that, just don’t drive it like it’s a Porsche.

You might have a lot of xp with being narced at depth and you probably handle yourself ok in a situation like that.
The problem starts when all rec divers think it’s fine to go deep on air, more accidents will happen and dive sites will be closed/stronger regulated.

 

[Celt]

Absolutely.

I can use helium and have access to it. With the rebreather, I will use very little so it makes financial sense to dive the right gas for the dive.

OC is out of the question for mainly deep diving. Just for a moment say helium cost nothing. Open Circuit deep diving is still a logistical nightmare as you need access to a compressor, booster and large volumes of helium and oxygen every night. A week's diving in Malin would need an entire 'J' cylinder*** for each diver, e.g. a whole one for helium and another one for oxygen. A boat load of 10 OC divers needing the best part of 20 'J' cylinders.

For CCR one J would last weeks as the volumes of both helium and oxygen are so low.


*** A 6ft/1m85 high 50 litre J cylinder at 200 bar contains 10,000 litres of helium (ignoring that you can't scavenge the last dregs of the cylinder). With a twinset containing 5,280 litres (2x12 at 220 bar), 45% of which is 2,376 litres of helium. For a laugh (although the gas monkey won't be laughing), call that 4 fills (as there'll be some residual gas in the twinsets). Thus one J feeds one diver for 4 or 5 days. Ten divers means ten J's.

And then there's oxygen. 50% and 80% for the deco gasses... Oxygen's getting expensive too.

Weekly deliveries of circa 20 J cylinders of gas to run a single Open Circuit dive boat!

Since you mentioned Malin head, let’s say a diver wished to dive a favourite wreck for Malin boats SS Justicia at 68m. If they wanted to maintain an END of 50m they would have to use 170 euro of helium to get 25 min bottom time. 16/23 An END of 60m would cost 70 euros. 10% helium But that’s one of the deeper Wrecks that people like to go to.