An escape filter device for engagement over the head of a wearer, comprises a protective hood made of a transparent foil, such as, a plastic material. The hood has an opening in the front which aligns with the mouth of the wearer into which a mouthpiece of a filter is attached. The filter has means for...http://www.google.fr/patents/US4154235?utm_source=gb-gplus-shareBrevet US4154235 - Escape filter device having protective hood
