Maskful

That maskful of sleeping gas was worse than the poison, worse than death itself.

The snorkels have automatic closing devices that usually work by gravity — which means little when a diver is upside down. A maskful of water isn't uncommon with these, but perhaps experience will show that you prefer one.

And there he was, some thirty minutes later, being placed on a stretcher by a muscular young paramedic, getting treated to a maskful of delicious oxygen that made breathing downright fun, if a gent can have fun under these kinds of circumstances.