Gas masks like this PH ( phenate hexamine ) Helmet were introduced by the British Army at the start of 1916. The fabric of these helmets were impregnated with chemicals designed to neutralise gas attacks and they featured a mouthpiece which the user could use to breathe out to prevent the build up of carbon dioxide. They were usually carried in small cotton haversacks worn over the shoulder. While users reported that they were uncomfortable to wear they provided generally adequate protection.