A gas mask is a mask used to protect the wearer from inhaling airborne pollutants and toxic gases. 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. Most gas masks are also respirators, though the word gas mask is often used to refer to military equipment, the scope used in this article. The gas mask only protects the user from digesting, inhaling and contact through the eyes. Most combined gas mask filters will last around 8 hours in a nuclear biological chemical (NBC) situation. Chemical specific filters can last up to 20 hours in an NBC situation.