The Hypo helmet, or British Smoke Hood (its official name), was an early British

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 gas mask

Gas mask

A gas mask is a mask put on over the face 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. Some gas masks are also respirators, though the word...

 in World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

.

The first use of poison gas on the Western Front

Western Front (World War I)

Following the outbreak of World War I in 1914, the German Army opened the Western Front by first invading Luxembourg and Belgium, then gaining military control of important industrial regions in France. The tide of the advance was dramatically turned with the Battle of the Marne...

 was on 22 April 1915, by the Germans at Ypres

Second Battle of Ypres

The Second Battle of Ypres was the first time Germany used poison gas on a large scale on the Western Front in the First World War and the first time a former colonial force pushed back a major European power on European soil, which occurred in the battle of St...

, against Canadian

Canadian Expeditionary Force

The Canadian Expeditionary Force was the designation of the field force created by Canada for service overseas in the First World War. Units of the C.E.F. were divided into field formation in France, where they were organized first into separate divisions and later joined together into a single...

 and French colonial

French colonial empire

The French colonial empire was the set of territories outside Europe that were under French rule primarily from the 17th century to the late 1960s. In the 19th and 20th centuries, the colonial empire of France was the second-largest in the world behind the British Empire. The French colonial empire...

 troops. The initial response was to equip troops with cotton mouth pads for protection. Soon afterwards the British added a long cloth which was used to tie chemical-soaked mouth pads into place, and which was called the Black Veil Respirator. Dr. Cluny MacPherson of Royal Newfoundland Regiment brought the idea of a mask made of chemical absorbing fabric and which fitted over the entire head to England, and this was developed into the Hypo helmet or the British Smoke Hood in June 1915. This primitive type of mask went through several stages of development before being superseded in 1916 by the canister gas mask of 1916.

The Hypo Helmet was the replacement, and was developed after Dr. MacPhersorn saw a German putting a bag over his head after a gas attack.

It was simply a khaki-coloured flannel bag soaked in hypo solution (glycerin and sodium thiosulphate); it protected against chlorine

Chlorine

Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

. The soldier placed it over his head and tucked the bottom into his tunic. No inlet or exhaust valve was provided, and the wearer's lungs forced the air through the material making up the bag. A fragile rectangular mica

Mica

The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition...

 or celluloid

Celluloid

Celluloid is the name of a class of compounds created from nitrocellulose and camphor, plus dyes and other agents. Generally regarded to be the first thermoplastic, it was first created as Parkesine in 1862 and as Xylonite in 1869, before being registered as Celluloid in 1870. Celluloid is...

 window provided visibility.

The first version was tested in May 1915; manufacture began in June and lasted until September, by which time 2.5 million had been made and the hood had been superseded by the P Helmet, which provided improved protection against chlorine and added protection against phosgene

Phosgene

Phosgene is the chemical compound with the formula COCl2. This colorless gas gained infamy as a chemical weapon during World War I. It is also a valued industrial reagent and building block in synthesis of pharmaceuticals and other organic compounds. In low concentrations, its odor resembles...

.