10. A PROTECTIVE HELMET COMPRISING AN OUTER SHELL OF AT LEAST TWO PIECES, GENERALLY SHAPED TO FIT THE HUMAN HEAD, SAID SHELL PIECES BEING HINGED TOGETHER SO THAT SAID PIECES MAY BE OPENED FOR ENTRY OF THE WEARER''S HEAD, ONE OF SAID SHELL PIECES INCLUDING A FACE OPENING, A TRANSPARENT VISOR THEREOVER AND A FLEXIBLE FACE SEAL FORMING AN ORAL-NASAL CAVITY THEREBETWEEN, MEANS FOR SUPPLYING OXYGEN TO SAID ORAL-NASAL CAVITY. AN EXHALATION VALVE IN COMMUNICATION WITH SAID ORALNASAL CAVITY, SAID HELMET INCLUDING A MOVABLE MEANS FOR MOVING THE WEARER''S HEAD FORWARD IN THE HELMET INTO ENGAGEMENT WITH THE FACE SEAL, SAID FLEXIBLE FACE SEAL BEING PRESSED POSITION TO MAKE SEALING CONTACT WITH THE WEARER''S FACE THEREBY MAXIMIZING HIS VISUAL FIELD, IMPROVING THE FACE SEAL AND ASSISTING IN PREVENTING AN INCREASED IN CO2 CONCENTRATION IN SAID ORAL-NASALL CAVITY.