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Gas in The Great War

James Patton, BS
Military Historian, U.S. Army Veteran, and WW-I Feature Writer

Every war brings to the fore a new way of maiming and killing soldiers. Gun powder in the 16th and 17th centuries meant that - finally, sadly - one could eliminate many of his enemies with one agent of offensive effort, an artillery round. Ultimately, in WWII it was demonstrated that a single atomic weapon could kill more than one hundred thousand of the enemy with a single use of a single weapon. While the efficiency of maiming and killing steadily advanced from the 17th to the 20th centuries it accelerated by an order of magnitude in WWI with the use of inhaled poison gasses.

One of the enduring hallmarks of WWI was the large-scale use of chemical weapons, commonly called, simply, ‘gas’. Although chemical warfare caused less than 1% of the total deaths in this war, the ‘psy-war’ or fear factor was formidable. Thus, chemical warfare with gases was subsequently absolutely prohibited by the Geneva Protocol of 1925. It has occasionally been used since then but never in WWI quantities. Production of some of these dangerous chemicals continues to this day as they have peaceful uses – for example, phosgene (carbonyl dichloride) is an industrial reagent, a precursor of pharmaceuticals and other important organic compounds.

Masked Soldiers Charge
Masked soldiers charge through a cloud of gas.

Several chemicals were weaponized in WWI and France actually was the first to use gas - they deployed tear gas in August 1914. The agent used was either xylyl bromide, which is described as smelling ‘pleasant and aromatic’, or ethyl bromoacetate, described as ‘fruity and pungent.’ Both are colorless liquids and have to be atomized to be dispersed as weapons. As lachrymatory agents, they irritate the eyes and cause uncontrolled tearing. Large doses can cause temporary blindness. If inhaled they also make breathing difficult. Symptoms usually resolve by 30 minutes after contact. Thus, tear gas was never very effective as a weapon against groups of enemy soldiers.

The German gas warfare program was headed by Fritz Haber (1868 – 1934) whose first try for a weapon was chlorine, which he debuted at Ypres in April 1915. Chlorine is a diatomic gas, about two and a half times denser than air, pale green in color and with an odor which was described as a ‘mix of pineapple and pepper’. It can react with water in the lungs to form hydrochloric acid, which is destructive of tissue and can quickly lead to death, or, at least, permanent lung tissue damage and disability. At lower concentrations, if it does not reach the lungs, per se, it can cause coughing, vomiting, and eye irritation. Chlorine was deadly against unprotected soldiers. It is estimated over 1,100 were killed in its first use at Ypres. Ironically, the Germans weren’t prepared for how effective it would be and were unable to exploit their advantage, gaining little ground.

Chlorine’s usefulness was short-lived. Its color and odor made it easy to spot, and since chlorine is water-soluble even soldiers without gas masks could minimize its effect by placing water-soaked - even urine-soaked - rags over their mouths and noses. Additionally, releasing the gas in a cloud posed problems, as the British learnt to their detriment when they attempted to use chlorine at Loos. The wind shifted, carrying the gas back onto their own men.

Phosgene (carbonyl dichloride) was Haber’s next choice, probably used first at Ypres by the Germans in December 1915. Phosgene is a colorless gas, with an odor likened to that of ‘musty hay’, but for the odor to be detectable, the concentration had to be at 0.4 parts per million, or several times the level at which harmful effects occur. Phosgene is highly toxic, due to its ability to react with proteins in the alveoli of the lungs, disrupting the blood-air barrier, leading to suffocation.

Soldiers Pose With Masks
Allied soldiers pose for a picture while wearing their gas masks.

Phosgene was much more effective and more deadly than chlorine, though one drawback was that the symptoms could sometimes take up to 48 hours to be manifest. The minimal immediate effects are lachrymatory. However, subsequently, it causes build-up of fluid in the lungs (pulmonary edema), leading to death. It is estimated that as many as 85% of the 91,000 gas deaths in WWI were a result of phosgene or the related agent, diphosgene (trichloromethane chloroformate).

The most commonly used gas in WWI was ‘mustard gas’ [bis(2-chloroethyl) sulfide]. In pure liquid form this is colorless, but in WWI impure forms were used, which had a mustard color with an odor reminiscent of garlic or horseradish. An irritant and a strong vesicant (blister-forming agent), it causes chemical burns on contact, with blisters oozing yellow fluid. Initial exposure is symptomless, and by the time skin irritation begins, it is too late to take preventative measures. The mortality rate from mustard gas was only 2-3%, but those who suffered chemical burns and respiratory problems had long hospitalizations and if they recovered were thought to be at higher risk of developing cancers during later life.

Gas Spreads Across A Battlefield
Windswept gas spreads across a battlefield in Europe.

Chloropicrin, diphenylchlorarsine, American-developed Adamsite (diphenylaminechlorarsine), and others were irritants that could bypass gas masks and make soldiers remove their masks, thus, exposing them to phosgene or chlorine.

Gases often were used in combinations. Most gas was delivered by artillery shells. The agent(s) were in liquid form in glass bottles inside the warhead, which would break on contact and the liquid would evaporate. Shells were color coded in a system started by the Germans. Green Cross shells contained the pulmonary agents: chlorine, phosgene and diphosgene. White Cross had the tear gases. Blue Cross had the ‘mask breakers’ like chloropicrin. Gold (or Yellow) Cross had mustard gas.

John Singer Sargent's Gassed
John Singer Sargent's 'Gassed' depicts the aftermath of a mustard gas attack on British troops.

In retrospect it is sad to know that warfare by poisoning soldiers - so brutal, highly personal, and used with such little restraint by both sides in WWI - had been previously outlawed by the Hague Convention in 1899. The ironies of gas warfare are vividly focused in the life of Fritz Haber, the German chemist who invented phosgene and also the ‘Haber Process’ which allowed fixation of atmospheric nitrogen into ammonia-based fertilizer. A German Jew who converted to Christianity, he received the Nobel Prize for Chemistry in 1919 for the Haber Process. Though long dead before The Holocaust, he was one of the chemists who perfected the hydrocyanide-based insecticides Zyklon A and Zyklon B, the latter gas used to kill millions of Jews and others, including some of his relatives.

The Imperial War Museum in London is the source of some of the images, particularly the John Singer Sargent painting, ‘Gassed.’ As very useful link to the popular media about gas warfare in WWI is: ‘How deadly was the poison gas of WW1?’ (

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