Gas Mask

A gas mask is personal protective equipment that seals over the nose and mouth, and sometimes the eyes and other soft facial tissue, to protect the wearer from inhaling airborne pollutants and toxic gases, and most gas masks also function as respirators, filtering out both gaseous agents such as chlorine or mustard gas and airborne particulates such as biological agents. Modern gas masks developed during the First World War used circular lenses of glass, mica or cellulose acetate for vision, with the more durable Triplex lens, a cellulose acetate layer sandwiched between glass, becoming standard into the 1930s before stronger polycarbonate lenses were later adopted. Most combined filters last around eight hours of exposure to a biological or chemical situation, though filters built for specific chemical agents can last up to twenty hours, and the mask may use one or two small screw on filter canisters or a larger filtration container connected by hose. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/