Mailing List Archive

Mailing List: techdiver

Message Display

At 4:29 AM 9/27/69, Richard Pyle wrote:
>On Thu, 9 Mar 1995, Scott Cherf wrote:

>First of all, I *don't* think semi-closed units are safer (that was the
>point of my message).  Yes, I was assuming the diver would not deliberately
>venture outside the range allowable with gases used.  I *COMPLETELY* agree
>with you that operator error is FAR more likely a problem than rig
>malfunction, both for fully closed and for semi-closed (I think this is the
>*main* problem rebreathers have had all along). However, I was only
>comparing rig designs, not considering operator variables.  I think both
>semi-closed and fully-closed are about equally complicated operationally
>(I actually think semi-closed are a little more complicated to
>operate...but since I have very little experience with semi-closed, I
>can't say for sure).

Right, I'm sorry about asserting your position was that semi-closed was
safer.  I should have said 'with respect to the potential for hypo/hyperoxia.
I got carried away because I've been carefully researching this issue
as I begin my rebreather training.  I agree that the semi-closed systems
appear to be more complicated, and that's the reason I believe the fully
closed systems will be safer in most operational scenarios.

>The reason for my stating that fully-closed had a higher *potential* for
>hypoxia/hyperoxia than semi-closed is because the replacement of
>metabolized O2 on a fully closed rig is usually almost entirely dependant
>on electronics (electronic sensors, solenoid, etc.), whereas the addition
>of oxygen in semi-closed systems is mechanical.

And this is the source of my concern over semi-closed systems.  The
mechanical systems used in constant mass semi-closed rebreathers absolutely
depend on the operator *not* going outside the depth envelope for the
mix, because they will *not* compensate and hyperoxia is virtually
certain if the diver goes to deep w/o adjusting the gas mix.  Add to
that the changes in O2 metabolism that come with variable workloads,
and it would seem that the semi-closed approach is more likely to lead
to hypo/hyperoxic conditions during use.

I suspect we are in violent agreement.

Scott.

Navigate by Author: [Previous] [Next] [Author Search Index]
Navigate by Subject: [Previous] [Next] [Subject Search Index]

[Send Reply] [Send Message with New Topic]

[Search Selection] [Mailing List Home] [Home]