Apparatus for forming an aperture, upon the occurrence of a predetermined event, in a resilient membrane such as a breathing hose, which is attached to a breathing mask worn by a person and which is partially filled with water due to immersion in the water followed emergence of a portion of the hose...http://www.google.co.uk/patents/US5156146?utm_source=gb-gplus-sharePatent US5156146 - Water-activated anti-suffocation protection apparatus
