The disclosed air filtration system filters both entering and exiting air. A primary structural element of the air filtration system is the unitary helmet member, which fits over the user's head. The unitary helmet member includes both a front aperture near the user's forehead and a rear aperture near...http://www.google.es/patents/US5592936?utm_source=gb-gplus-sharePatente US5592936 - Surgical helmet
