how long does black diamond claim you can...
how long does black diamond claim you can breath thru the tube
They don't have a set length of time that it will work, because it varies according to things like the snowpack, how loose it is, how wet it is, how fast the user is breathing, and many other factors. It will help you survive, but don't count on it for a long period of time.
In the field tests for the Avalung pack the buried subject got bored after about forty minutes and they dug him out. He If you are burried in a real avalanche though the situation is likely to be a lot different. I guess if you are buried without any bodily trauma with the avalung in your mouth then you could probably last a while but every situation is different. It is best not to fully rely on any piece of avy gear and just play it as safe as possible. But on the other hand It has saved lives .