Posted by Ueli (22.214.171.124) on September 19, 1999 at 17:02:55:
In Reply to: o2 masks posted by steve on September 18, 1999 at 23:51:37:
What do you mean with Co? Cobalt or carbon monoxide CO? I wouldn't go near a place where either of these were in more than the smallest trace amount. Or do you mean CO2 (carbon dioxide)? Yes, that's the waste product that we exhale, it makes up less than 1% of our 'exhaust'; but breathing a gas mixture with more carbon dioxide then oxygen, you would drop dead within 5 minutes. In fact, breathing in a closed room where the CO2 concentration approaches 1% (and oxygen still above 20%) would make you extremely dizzy and prone to faint.
With a standard mask, it is possible to suck in outside air through the exhaust holes and this must be counteracted by a high O2 flow rate. Mask of 'geriatric' type are even designed to suck in air with the O2 jet and are quite useless for our purpose.
Non-rebreather masks have a one way flap over the exhaust and while breathing in, O2 is supplied from the reservoir bag.Therefore, as Michelle C states absolute correctly, it is possible to use this type of mask at a lower flow rate. I've gone down to 5 l/min on weekends when in danger of running out of O2 before Monday, without noticeable reduction of effectiveness.
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