The '''P helmet''', '''PH helmet''' and '''PHG helmet''' were early types of [[gas mask]] issued by the [[British Army]] in the [[First World War]], to protect troops against [[chlorine]], [[phosgene]] and [[tear gas]]es. Rather than having a separate filter for removing the toxic chemicals, they consisted of a gas-permeable hood worn over the head which was treated with chemicals.
The PH Helmet (Phenate Hexamine) replaced it in October 1915, and adddedadded hexamethylene tetramine, which greatly improved protection against phosgene<ref>[http://www.gutenberg.org/dirs/etext98/rrhin10.txt The Riddle of the Rhine: Chemical Strategy in Peace and War], Victor LeFebure, at Project Gutenberg</ref> and added protection against hydrocyanic acid.<ref>[http://www.eustis.army.mil/dtpmsec/NBC_School/Mask%20History.pdf History of the U.S. Army's protective mask]</ref> Around 14 million were made and it remained in service until the end of the war by which time it was relegated to second line use.
The PHG Helmet appeared in January 1916 and was similar to the PH Helmet but had a facepiece made of rubber sponge to add protection against tear gas. Around one and a half million were produced in 1916-1917.
It was finally superseded by the [[small box respirator]] in February 1916, which was much more satisfactory against high concentrations
