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>By using the partial mask , which has one of the one way valves removed, if
>the oxygen supply becomes depleted the patient will still be able to breathe
>through the open port

I think you've got the partial rebreather confused with the modified non-
rebreathers that seem to be all you can buy these days. The difference
between a non-rebreather and a partial rebreather is that the non- has a
one way valve between the reservoir and the mask, so none of the exhalation
goes back into the reservoir. A partial rebreather doesn't and can't
provide more than 60% no matter what the flow.

Unfortunately, for the reasons you mention, the non-rebreather masks
available have been modified by putting the air vent in place of one of the
two exhalation valves they used to have

This is probably a good idea in general, but not for dive/DCS treatment,
where achieving a high PO2 is more important than it is in most other
emergency situations.

The other problem with the vent is that, along with making it impossible to
obtain FO2's over 90% or so, it requires really cranking up the flow to get
even that. Once again, not a problem for med/EMT types, who have unlimted
O2 on hand, but a drag with a single D tank and an hour from shore.

 The OXY HACKER suggests pirating a valve from another mask and fitting it
to the  non-rebreather mask in your dive O2 kit, taping over the air hole,
or covering it with a finger in order to get the highest possible FO2.

 If anyone knows of a source of the old style masks without the hole, let
us know - I'd really like to get some. It's too bad DAN won't address this,
considering how they are always going on about how critical that last 5-10%
of O2 is.


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