caver95(Offline)

I was told divers of the RB80 are tought to come off the loop for accent. Is this true and if so why is that? Thanks. Nick Leone

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Little Pete(Offline)

It might be something to do with the ascent reducing the O2 pp in the loop and by going open circuit it prevents this affecting the diver.

However, I've never dived a rebreather and have no proper understanding of the RB-80 so I might be (read probably am) wrong.

If you're interested then get on a course for the unit

Richard Lundgren(Offline)

Its refered to as FiO drop and there are several ways of dealing with this. One way is to flip to OC while ascending (this being the safets way). If you know what you are doing you could clear the loop and ascend and repeate this untill the gas cant be used, due to the FiO drop, or you hit your gas switch depth.

Take care,
Richard Lundgren

caver95(Offline)

I dive a rebreather. I know that the po2 will drop, but there is no need to come off the loop on my unit or even a dreager.

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EBT(Offline)

Kev,

Thats because you're planning your deco differently, that and the RB80 vents a lot less than something like a Drager (i seem to recalls is 1:8 or 1:10 ratios).

No doubt Richard can tell me just how wrong I am


/Zak

caver95(Offline)

i know they vent differently, why would you plan your deco diffently??? calc your Fio2 and figure it out from there? do your gas switchs and stay on the loop, why would you want to get off the loop?

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davy(Offline)

I'm not a RB-80 diver, but if I recall correctly there used to be 2 RB-80 courses.

The first being a somewhat "recreational" course that used only one single gas, thus no switch block.
The other "full" course implemented everything like switching gasses.
(this might be changed in the new standards)

Then for the "first" course they would teach to ascent and descent on OC mode...
Seems logical because if you were using a mix like 21/35 it would be essential to do this in OC mode since with a 1:10 ratio it would become hypoxic above 10-12m
Even a 32% nitrox mix would become hypoxic on the surface with about 5-7% O2 left...

So with these standard gas mixes you either have to switch gasses on ascent or go to OC; and since the first course doesn't teach gas switches OC on ascent if the safest option.

correct me if I'm wrong

anders(Offline)

Not an RB diver, nor having intentions of becoming one but:
Couldn´t you just vent the thing by blowing gas out your nose, and there by triggering inspiration of "fresh" gas?

lizardland(Offline)

The RB80 has a massive drop in ppO2 in the loop on ascent. The RB80 maintains the ppO2 by dumping a certain amount of gas which causes the loop volume to reduce which causes the ADV to fire and inject fresh gas. On the ascent the gas in the loop is expanding so the loop volume never reduces to cause the ADV to fire. That combined with physics (the pO2 will drop on its own anyway) can make the gas hypoxic. It is not uncommon for the diver to be in a position where he cannot safely ascend on the drive gas, even relatively simple dives need two gases if the loop is to be stayed on.

There are procedures that avoid this, you can switch gases (hassle), you can do flushes manually (wasteful) or you can switch to OC.

The simplest procedure is to buy another rebreather.

There are two problems with this, one you have to remember to do it. If there are a million other things going on then you are in trouble. Second, there is a hell of a lot of gas to exhale in an expanding loop.

caver95(Offline)

Switching to oc is not wasteful?

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