A gas mask may be the most important survival item you ever buy, and an essential item for your Bug Out Bag. A gas mask is a mask that one can put on over the face to help protect the user from inhaling airborne pollutants and toxic gasses. The mask forms a sealed cover over the nose and mouth, but may also cover the eyes and other vulnerable soft tissues of the face.
Some gas masks are also respirators, though the word gas mask is often used to refer to military equipment (e.g. Field Protective Mask, etc.) Click the link below to see the full, amazing article on this subject
(Picture Credit: science.howstuffworks.com)