I did some hostile environment training a while back, one of the medical courses was about "sucking chest wounds", where someone gets shot (or stabbed), and the action of breathing fills the chest cavity and thus means the lung can't work.

It's been a long time since I did the course as I went a few years without having to travel to the kinds of places where it's likely I'd need to apply it, but I do remember a plastic bag and vasseline was recommended if you didn't have a magic sucking chest wound plastic cover thing with a valve on (our med kits contain things like that and tourniquets as well as the usual stuff - including packs of sterile needles etc).