N2 rising when flying

Hello,

anyone that could have an explenation for this?
As I am wearing my Descent Mk1 when flying, the N2 percentage in the widget rise up to about 40% (the cabin preasure corresponds to about 2000m). That is without diving before the flight, so the N2 starts at 0%.
I understand that the N2% rise when descemnding in a dive and then slowly decline over time when ascended again...
But why does the N2% rise when flying and the air presure decreases? When going down and landing, the N2% decrease to 0% again.

I have asked garmin about this but did not get any good explenation...

Top Replies

atj777 over 6 years ago +1

I suspect it is showing you your N2% relative to the current pressure. At the surface your tissues are saturated with N2 at 1 ATM. When the cabin of the plane depressurises your tissues are now supersaturated…

All Replies

0 atj777 over 6 years ago

I suspect it is showing you your N2% relative to the current pressure. At the surface your tissues are saturated with N2 at 1 ATM. When the cabin of the plane depressurises your tissues are now supersaturated with N2. When the cabin repressurises, you will actually be less than saturated as you will have off-gassed during the flight but I suspect it doesn't show negative percentages so it just shows zero.

What I mean here is that 0% is "normal" saturated with N2. 100% would be the tipping point where N2 could bubble out. Anywhere in between means your tissues are more than saturated.

0 Milosherman over 6 years ago

Thank you atj777,

yes, I guess this explains it.
But does it make sense...? Perhaps it does. If I would have a saturation let´s say 20% after a dive and then went flying, it would add the 40% due to the depressurizing of the cabin ending up with 60% N2?

0 atj777 over 6 years ago

Which is why you shouldn't fly straight after diving.

0 JonathonBellman over 6 years ago

I was curious as to the pressure in the cabin during a flight, so i googled it. this link turned out to be an interesting read:

https://www.quora.com/How-does-cabin-pressure-in-a-plane-change-with-altitude-before-it-reaches-10-000-feet-is-the-plane-pressurized-to-4000-feet-at-4000-feet-ASL

It does make sense though. In flight the air is at a higher pressure than sea level, therefore you are experiencing some N2 loading, just as you would whilst diving.

0 atj777 over 6 years ago

n flight the air is at a higher pressure than sea level, therefore you are experiencing some N2 loading, just as you would whilst diving.

The pressure in the aircraft is LOWER than the air pressure at sea level but HIGHER than the air pressure outside the aircraft. That's why you need to wait 12-24 hours after diving before you fly or you risk DCS from the LOWER pressure. You experience (some) N2 offgassing while flying not loading.

0 scarboroughjohn over 3 years ago in reply to atj777

I have been watching this for a few years the watch thinks you have been diving at sea level for several months and now you have "surfaced to cabin pressure" (much higher on boeings than airbus incidentaly). So all tissues are saturated at , in my case, 46%. The next fun think is you get the "no flytime" screen ... while you are flying. Awesome technology!