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Why do we use 50% and 100% as Deco Gas?

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Why do we use 50% and 100% as Deco Gas?

Post Number:#1  Postby Nizaha » Sun Dec 14, 2008 6:32 am

Something to do during winter.

Someone may ask why do we use 50% and Oxygen during our deco. We know the optimal PO2 for decompression is between 1.0 and 1.6ata. The benefit of using 50% and Oxygen is that our PO2 never drop far below 1.0ata for any stop depth between 70ft(21mtr) and the surface. These gases also allow us to get on then at their respective MOD (Maximum Operation Depth) and take advantage of the 1.6PO2. In effect this create somewhat of a vacuum to remove inert gas from your body or and Oxygen window.

The oxygen window basically loading arterial blood with Oxygen forcing inert gas in the tissues to be forced out.The oxygen window actually greatest while using Oxygen during 20ft (6mtr) stop.  It's a great different between partial pressures in arterial blood and the tissues. In addition when we make the gas switch 70ft (21mtr) we extend that stop to 4minutes to optimize this high PO2 situation. Will take few minute for High PO2 blod to circulate through the body after inhaling the gas.

I don't know but there's argument for it that are all flawed. First thinking that Oxygen is a buoyancy risk just a false. Breathing any gas at the PO2 of 1.6ata would be pose the same risk, also if you can't control your buoyancy at certain depth you should not clarified you as a Technical diver. 80% O2 also only gives you a PO2 1.5 at 3ft (10mtr), throwing the benefit right out the Window.

From an equipment point of view not only is Oxygen easy to mix but if we only ever put O2 in a tank we don't need to worry about the cleanness. Being said that most technical divers now days mark their deco bottle permanently with appropriated MOD. Proper markings are he permanent MOD is 3in letter horizontally on both sides of the cylinder as the analyzed MOD on the crown. Included me I use luxfer 40cf for 100% for Oxygen and Luxfer 80cf for 50% marked with 70ft.

Here My bottle Picture.. Clean and clear setup..
Image

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Zaha
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#2  Postby John F SeaDemon » Sun Dec 14, 2008 9:49 am

Easier to calculate too in case of lost gas...ie. lost of O2...double the time using 50%
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#3  Postby Snafu » Sun Dec 14, 2008 11:51 pm

Errrr how do u force inert gas out of the tissues by using higher % of O2 ?

Sure or not.... [-(

Do look at how inert gas were removed from tissues...fats from the body.

Do you think using from lower % of O2 being use as bottom gas & then switch to higher % O2 is good or adding risk?

:D
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#4  Postby Nizaha » Mon Dec 15, 2008 9:34 am

Hi Mr Snafu  :hello: :hello:

Gases dissolve out of our blood and into the lung alveoli (air spaces in lung).  Gases always move from high concentration to low concentration.  So if you have high concentration of nitrogen dissolved in your blood (i.e. when diving or after surfacing) and you breathe air, nitrogen still dissolves out of your blood (i.e. tissues) and into your lungs where you breathe it out.  But you get the greatest nitrogen release if you breathe 100% oxygen because the nitrogen has a big concentration gradient.

I hope this help ... ;)

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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#5  Postby Sicko » Mon Dec 15, 2008 11:13 am

John F SeaDemon wrote:Easier to calculate too in case of lost gas...ie. lost of O2...double the time using 50%

Bro, can use 40% & 80%? calculations should also be the same?(double the time)

But I prefer 50% & 100% as pure O2 allows for a greater O2 window.

:)
Anyone can do a dive to 100m or more.....
But how many will return alive???
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#6  Postby Sicko » Mon Dec 15, 2008 11:25 am

Syed K. A. wrote:Do you think using from lower % of O2 being use as bottom gas & then switch to higher % O2 is good or adding risk?

:D

It's a trade off...........one can deco fully on bottom gas, but will need plenty of it!!!

High PPO2 is always a risk.........the question is just how high a PPO2 can one tolerate?

:)
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But how many will return alive???
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#7  Postby Sicko » Mon Dec 15, 2008 11:35 am

Nizaha wrote:Hi Mr Snafu  :hello: :hello:

Gases dissolve out of our blood and into the lung alveoli (air spaces in lung).  Gases always move from high concentration to low concentration.  So if you have high concentration of nitrogen dissolved in your blood (i.e. when diving or after surfacing) and you breathe air, nitrogen still dissolves out of your blood (i.e. tissues) and into your lungs where you breathe it out.  But you get the greatest nitrogen release if you breathe 100% oxygen because the nitrogen has a big concentration gradient.

I hope this help ... ;)

Safe Diving
Zaha

I don't know about concentration gradient but my view is that you are no longer introducing N2 into your body when breathing O2. Therefore allowing for more N2 to be off loaded.

:)
Anyone can do a dive to 100m or more.....
But how many will return alive???
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#8  Postby Sicko » Mon Dec 15, 2008 11:36 am

BTW, anyone tried deco at 10m using O2?
Anyone can do a dive to 100m or more.....
But how many will return alive???
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#9  Postby Nizaha » Mon Dec 15, 2008 8:46 pm

Sicko wrote:
Nizaha wrote:Hi Mr Snafu  :hello: :hello:

Gases dissolve out of our blood and into the lung alveoli (air spaces in lung).  Gases always move from high concentration to low concentration.  So if you have high concentration of nitrogen dissolved in your blood (i.e. when diving or after surfacing) and you breathe air, nitrogen still dissolves out of your blood (i.e. tissues) and into your lungs where you breathe it out.  But you get the greatest nitrogen release if you breathe 100% oxygen because the nitrogen has a big concentration gradient.

I hope this help ... ;)

Safe Diving
Zaha

I don't know about concentration gradient but my view is that you are no longer introducing N2 into your body when breathing O2. Therefore allowing for more N2 to be off loaded.

:)
[/
Sicko wrote:
John F SeaDemon wrote:Easier to calculate too in case of lost gas...ie. lost of O2...double the time using 50%

Bro, can use 40% & 80%? calculations should also be the same?(double the time)

But I prefer 50% & 100% as pure O2 allows for a greater O2 window.
:)


Hi Sicko


PPO2's far lower than 1.6 or 1.4 are still toxic given enough time and PPO2's well above 1.6 can be tolerated for short times. Short term problems with high PPO2 also include central nervous system problems up to and convulsions might appears, normally he diver is likely to lose his reg and then drown.The specific times are where it gets interesting as they can vary from diver to diver, from day to day and work loads.

Safe Diving
Zaha
Last edited by Nizaha on Mon Dec 15, 2008 8:51 pm, edited 1 time in total.
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#10  Postby Nizaha » Mon Dec 15, 2008 8:48 pm

Sicko wrote:BTW, anyone tried deco at 10m using O2?


I would say NO for myself.

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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#11  Postby Nizaha » Mon Dec 15, 2008 8:52 pm

Sicko wrote:
Nizaha wrote:Hi Mr Snafu  :hello: :hello:

Gases dissolve out of our blood and into the lung alveoli (air spaces in lung).  Gases always move from high concentration to low concentration.  So if you have high concentration of nitrogen dissolved in your blood (i.e. when diving or after surfacing) and you breathe air, nitrogen still dissolves out of your blood (i.e. tissues) and into your lungs where you breathe it out.  But you get the greatest nitrogen release if you breathe 100% oxygen because the nitrogen has a big concentration gradient.

I hope this help ... ;)

Safe Diving
Zaha

I don't know about concentration gradient but my view is that you are no longer introducing N2 into your body when breathing O2. Therefore allowing for more N2 to be off loaded.

:)


correct!

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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#12  Postby John F SeaDemon » Tue Dec 16, 2008 2:01 am

Sicko wrote:
John F SeaDemon wrote:Easier to calculate too in case of lost gas...ie. lost of O2...double the time using 50%

Bro, can use 40% & 80%? calculations should also be the same?(double the time)

But I prefer 50% & 100% as pure O2 allows for a greater O2 window.

:)


Bro, I love going through the trouble to O2-clean my reg.  If I want to use 40% I'll stick to looking at Nemos.  And I don't like the number 40.  :D :D :D :D :D
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#13  Postby John F SeaDemon » Tue Dec 16, 2008 2:04 am

Sicko wrote:BTW, anyone tried deco at 10m using O2?


Urrgh...that's high PPO2. Unless you plan to do IWR. But you should go down to 18m then :P :D :D :D :D
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#14  Postby Sicko » Tue Dec 16, 2008 8:19 am

John F SeaDemon wrote:
Sicko wrote:
John F SeaDemon wrote:Easier to calculate too in case of lost gas...ie. lost of O2...double the time using 50%

Bro, can use 40% & 80%? calculations should also be the same?(double the time)

But I prefer 50% & 100% as pure O2 allows for a greater O2 window.

:)


Bro, I love going through the trouble to O2-clean my reg.  If I want to use 40% I'll stick to looking at Nemos.  And I don't like the number 40.  :D :D :D :D :D

:D :D
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But how many will return alive???
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#15  Postby putradiver » Mon Feb 16, 2009 8:30 pm

Don't be to excited to use O2.  Remember to calculate the OTUs also.  Depends on the dives, time and logistics, rather use the 80% coz u may cut down the OTUs while giving almost the same benefits as the O2.

The Army Assault Swimmers SOPs on Lar V, max 10m.  (hope they change it soon).

Take care guys
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#16  Postby Sicko » Tue Feb 17, 2009 12:48 pm

putradiver wrote:Don't be to excited to use O2.  Remember to calculate the OTUs also.  Depends on the dives, time and logistics, rather use the 80% coz u may cut down the OTUs while giving almost the same benefits as the O2.

The Army Assault Swimmers SOPs on Lar V, max 10m.  (hope they change it soon).

Take care guys

Hi bro,
For recrational tec diving that only last a few days at most, you will most proberbly not even go near the recommended OTU prescribed.

IMHO, 80% will not be a better deco gas as N2 is not minimised.

A better way to deco on O2 may be to use air breaks to minimise O2 tox proberbility.

:)
Last edited by Sicko on Tue Feb 17, 2009 12:52 pm, edited 1 time in total.
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But how many will return alive???
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#17  Postby putradiver » Tue Feb 17, 2009 9:06 pm

Bro, as i said, Depends on the dives, time and logistics.  ;)
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#18  Postby Scooter » Wed Feb 18, 2009 1:58 pm

Are you guys actually go technical diving or only write about it?

At the end of the day beside your pros and cons regarding off-gasing choosing 80% instead of oxygen is just not practical.
For example if you are on a LOB 3 days at the Repulse 50% & 100% is the way to go. Every 2-3 dives you blend a new 50%. You carry a 7 liter O2 as standby which you don’t have to touch during the entire trip unless you drift. For 6 m and above you use the surface supplied oxygen at the deco bar.
But if you choose 50% and 80% you end up blending most of the time during the intervals. In addition on commercial LOBs the surface supplied O2 is normally FOC whereby 80% blends cost you most of the time extra.

Just some practical thoughts!
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#19  Postby Snafu » Wed Feb 18, 2009 4:32 pm

I would go for EAN60 n 100% O2 for my choice of gas.

EAN60 is what I would use for deco & 100% for emergency....but in the end of the day I would look into the water condition n max depth I plan to go + deco PPO2 I be using, I dont really do 1.6Bar PPO2 for deco.

Anyway is all theory except for BENDs.

Tolerance of O2 toxicity from each person are different....but for sure U will get HIT if U push the limit, so be conservative.... 5..10...15mins slower in getting out of the water are always safer then being the 1st on deck  :laughing11: after all u only doing the dive for FUN so why take the risk.

Just my own opinion without doing the dives.

:D
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#20  Postby Sicko » Wed Feb 18, 2009 8:57 pm

Scooter wrote:Are you guys actually go technical diving or only write about it?

Can't dive now.........so the next best thing is to write something about it!!!  ;)
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Re: Why do we use 50% and 100% as Deco Gas?

Post Number:#21  Postby Nizaha » Thu Apr 16, 2009 12:28 am

Scooter wrote:Are you guys actually go technical diving or only write about it?

At the end of the day beside your pros and cons regarding off-gasing choosing 80% instead of oxygen is just not practical.
For example if you are on a LOB 3 days at the Repulse 50% & 100% is the way to go. Every 2-3 dives you blend a new 50%. You carry a 7 liter O2 as standby which you don’t have to touch during the entire trip unless you drift. For 6 m and above you use the surface supplied oxygen at the deco bar.
But if you choose 50% and 80% you end up blending most of the time during the intervals. In addition on commercial LOBs the surface supplied O2 is normally FOC whereby 80% blends cost you most of the time extra.

Just some practical thoughts!




I just a normal diver. I log 35 dives last year in technical diving around Canada depth between 40mtr to 60mtr, mostly normoxic or trimix. Not many Technical liveaboard has O2 Bar. To have O2 Bar is a dream to every Tech divers. I rather carry O2 bottle in case I lost the main line or anchor line during the dives( Worst case scenario). Current, Low visibility which is apply in my diving condition. I don't mind carry 3 stage on me rather reliable on O2 Bar. My Deco gas will be 50% and O2.. for sure.

Doesn't hurt to anyone wrote something here, I am sure they know what they doing here.We'll learn here.

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Zaha
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