I am still very new to cannula delivered O2 and, frankly, still a little confused.
I have an eight place cabin class aircraft, so cannot individually supervise the health and sats of every passenger.
We have three O2D2s, one for P1 and P2, and one each side for the pax in rows 2 and 3. (We decided that we would never be eight-up in a cruise, so we haven’t equipped the rearmost two seats.)
Flying for the first time with my wife using O2, we decided that she would sit in P2 so I could supervise her. (She usually sits in Row 2, without headphones, and reads).
Many times on the outbound journey we got the rapid de-de-de-de alarm, and I looked in the manual and interpreted it as low input pressure, so turned the cylinder up to the maximum permitted by MH, 1.7 bar. I also gave her a flared cannula, which seemed to work better for her.
This seemed to make things a little better, but we still got the alarm from time to time, and my wife was getting anxious*, so I limited our altitude to 150 and very regularly checked both our sats. I was solid at 92 and she at 98 (sic, 98).
Before the return journey, I carefully checked that none of the pipes was crushed or kinked and the pressure right up at 1.7 bar, and we flew back at 130 to reassure her that there was no possibility of conking out (she has flown hundreds of times at 130 without O2). This was to remove any panic-induced effects.
On the way back we still got a few alarms and I did some experimenting:
Now, the reason I am going to such lengths to describe all this is that I am concerned that cannulas are not a reliable way to deliver O2 to passengers who are not in close contact with the pilot, and not having their sats checked. I am sure that it’s fine with two or three people in an SEP, but I am worried about a cabin class aircraft where the pax are distant and out of contact.
I don’t really know the question(s) I am asking here. Please look on it all as “unknown unknowns” and advise! 
* (she is still alarmed by the “approaching altitude” sound on the Aspen, even though I have explained it many times – she is a very nervous passenger (which will surprise those of you who know her on the ground, where she is the picture of poise and self confidence.))
From what you write, it doesn‘t sound like you are having problems with cannulas; it sounds more like you are having problems with the O2D2.
Btw, if you are new to cannulas, what have you been using before that?
boscomantico wrote:
if you are new to cannulas, what have you been using before that?
Normally aspirated air.
I’ve never used a O2D2 but sounds like you have the apnea alarm rather than the low input pressure alarm.
Xtophe wrote:
you have the apnea alarm rather than the low input pressure alarm
Yes, that is the conclusion I came to on the return journey.
FWIW i had to return an MH device for the same reason. No alarm with the very setting.
Normal breathing controlled flows → alarm.
Got a new MH and all works fine now.
The canulas are fine at my levels (max F150 so far), above MH recommends the small masks.
Dont like them, though
I use O2D2 almost 5 years without any problem. I have 3 units, keeping one as a spare and rotating them to be sure everything is in working order. The average consumption is 30-40 psi per person per hour at FL160-180 (DA42 – 50 cuft cylinder).
I think you simply have to learn to breathe differently if using a cannula. Essentially, you need to breathe in AND out through your nose. Took me a couple of flights after I got my O2 system to figure it out (I’m not using MH, but a similar Oxymiser system). That your wife’s O2 level drops when she speaks doesn’t surprise me – exhaling and/or breathing through the mouth circumvents the system. It just takes a little while to fine tune both the system and your breathing. That said, I’m not familiar with the O2D2, so there may, as others have said, also be an issue there.
ch.ess wrote:
(max F150 so far), above MH recommends the small masks.
180?
Sorry Timothy, confusing abbreviation on my part. The TB20 has a ceiling of 18000ft, i have taken it to max FL150 (slowly ….) .
And MH recommends masks from FL180, indeed – so I will not need them ;-)
172Driver, as far as I can tell after testing and checking with a MH rep., breathing has no relevance for the O2D2. It is a momentary drop of the pressure that triggers the o2 release.
If you have shallow breathers as passengers, you have to tell them to take deep breaths – or fly in a way that they do ;-)
