The thing that kills most people who are "simply" buried in an avalanche (and not pulped as they're carried through the tries or into a rock) is actually the CO₂ concentration in the snow around their nose and mouth building up over time.

I have a piece of avalanche survival kit made for skiers/snowboarders called the "AvaLung" in my off-piste bag. It draws air in from around the face, and vents your exhalations out behind you. People have survived being buried an hour or more wearing one of those.