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In the 70', CJ Lambertsen discovered that, under certain circumstancies, wrong switches of breathing mixures can increase the total amount of inert gases in the body and can induce DCI, even with no change in the depth (ambient pressure). That's a DCI induced by an Isobaric Inert Gas Counterdiffusion. The experience involved argon and helium gases and the troubles were also located in the skin depending of the nature of the gas in the dry chamber (but don't worry if you have air in your drysuit during a trimix dive ...).

This ICD can also hapened when a diver switch from "a slow gas & high dissolution property" like nitrogen, to a "fast gas & low dissolution property" like helium. In this case, helium is entering faster than nitrogen is leaving and, during a while, the sum up of both inert gases is increasing, even with no change in the ambient pressure.
Usually, the switch from nitrogen to helium only hapen (in OC) during the descent. But, at this moment, the diver is "under saturated" and there is no risk. During the ascent, the diver switches from helium to nitrogen ("fast gas" to "slow gas"), there is no risk of increasing the sum up of inert gases during the deco stop. So, this kind of counterdiffusion is not a concern for the diver except if a very "brave and smart" diver is coming back from a deep air dive and has the idea to switch with an heliox mixture at the deco stop ???

However, if this kind of counterdiffusion can be dangerous (slow gas to fast gas), the opposite should be good (fast gas to slow gas). It should increase the offgasing and reduce the deco time obligations. But, it's not so safe!
Divers switching from trimix to air during the ascent often got ear troubles. The CDG article is discussing about this case of counterdiffusion. It's an interesting article but I don't agree with the conclusion.

So, there are two kind of counterdiffusion :
1- Nitrogen --> Helium : This one is dangerous for the diver. It can induce an oversaturated status even in isobaric conditions. But it should never hapen. So, we don't care about it.
2 - Helium --> Nitrogen : This one should be good for the diver (accelerate the offgasing), but it's not and we don't really know why.
So, the best is to avoid the situation where one inert gas is ongasing while another one is offgasing.
With CCR, it's easy : don't switch !
With OC, only use trimix with the same nitrogen percentage (more or less) in every mix. The best would be to keep the same PN2, but not easy to do. And do not forget that Surface is another breathing gas switch.

Erik Rådström 2010-09-14 14:26:52
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Rebreather bailout	Erik Rådström	2010-09-13 13:36
Sv: Rebreather bailout	Anders Thulin	2010-09-13 19:24
Sv: Sv: Rebreather bailout	Dmitri Gorski	2010-09-13 19:46
Sv: Sv: Sv: Rebreather bailout	Erik Rådström	2010-09-13 20:00
Sv: Sv: Sv: Sv: Rebreather bailout	Dmitri Gorski	2010-09-13 20:52
Sv: Rebreather bailout	Johan Niemi	2010-09-14 09:08
Sv: Rebreather bailout	Magnus L	2010-09-14 09:16
Sv: Sv: Rebreather bailout	Magnus L	2010-09-14 09:31
Sv: Sv: Sv: Rebreather bailout	Erik Rådström	2010-09-14 09:56
Sv: Sv: Sv: Sv: Rebreather bailout	Peter Svensson	2010-09-14 12:25
Sv: Sv: Sv: Sv: Sv: Rebreather bailout	Erik Rådström	2010-09-14 12:56
Sv: Sv: Sv: Sv: Sv: Sv: Rebreather bailout	Peter Svensson	2010-09-14 13:26
Sv: Sv: Sv: Sv: Sv: Sv: Sv: Rebreather bailout	Erik Rådström	2010-09-14 13:32
Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Rebreather bailout	Erik Rådström	2010-09-14 14:26
Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Rebreather bailout	Erik Rådström	2010-09-14 14:29
Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Rebreather bailout	Dmitri Gorski	2010-09-14 16:58
Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Rebreather bailout	Richard Lundgren	2010-09-15 20:32
Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Rebreather bailout	Erik Rådström	2010-09-16 09:37
Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Rebreather bailout	Jonas Pavletic	2010-09-18 23:08
Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Rebreather bailout	Erik Rådström	2010-09-19 22:52
Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Sv: Rebreather bailout	Jonas Pavletic	2010-09-20 23:17
Sv: Sv: Sv: Sv: Rebreather bailout	Magnus L	2010-09-14 17:30
Sv: Sv: Rebreather bailout	Jonas Pavletic	2010-09-16 00:53
Sv: Sv: Sv: Rebreather bailout	Erik Rådström	2010-09-16 11:26
Sv: Sv: Sv: Sv: Rebreather bailout	Dmitri Gorski	2010-09-16 14:13
Sv: Sv: Sv: Sv: Sv: Rebreather bailout	Erik Rådström	2010-09-16 15:02
Sv: Rebreather bailout	Mats Horngren	2010-09-15 15:45
Sv: Rebreather bailout	Nico Dolovski	2010-11-27 15:26
Sv: Sv: Rebreather bailout	Tomas Persson	2010-11-27 18:37
Sv: Rebreather bailout	Nico Dolovski	2010-11-27 23:08
Sv: Rebreather bailout	Calle Lundin	2010-11-28 09:36

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