Soeben fand ich auf Facebook diesen Text eines Tauchlehrers auf den Malediven (Insel Gan) zu dieser Vollgesichtsmaske. Sehr interessant! Sorry, leider auf Englisch.
"Snorkeling can be safe if you are fit, know the envirionment where you go snorkeling and if you use the right equipment, like mask, snorkel and fins.
One hype at the moment are those full face masks, those are promoted as easy to use but as a diving professional I prefer to say easy to die!! I will mention one important reason why I say this.
1 - like the most people know we breathing air, air has about 21% oxygen and 78% nitrogen 1% rest gas. Everytime we breath in we breath 21% oxygen but when we breath out we breath out about 17% oxygen and 4% carbon dioxide. The problem with those full face mask is the 4% carbon dioxide will not be breath out in the open air but will be kept inside your mask and snorkel.
This means the next breath you take, you will breath in the "old" air with the 4% carbon dioxide and 17% oxygen, this can and / or will create serious problems and can even cause a blackout, drowning as an result.
If you want go for snorkeling, go to a professional dive shop. Ask advice, buy safe equipment, be fit and know your snorkel envirionment."
Der dargestellte Problemkreis entspricht dem Atmen in einer über den Kopf gezogenen Mülltüte.