A head cover and safety helmet having detachable ventilating means, and removable filter collar. The head cover, or shell, is formed of rigid material, having a face opening with a primary transparent shield yieldably mounted thereon, and multiple secondary transparent shields yieldably mounted on the...http://www.google.es/patents/US4455687?utm_source=gb-gplus-sharePatente US4455687 - Head cover and safety helmet
