“I wish those people who talk about going on with this war whatever it costs could see the soldiers suffering from mustard gas poisoning.”
Vera Brittain, First World War nurse
“The use in war of asphyxiating, poisonous or other gases has been justly condemned by the general opinion of the civilized world.”
OF ALL THE grim legacies of the First World War, none achieved the infamy of poison gas.
Despite prohibitions under the 1899 Hague Declaration Concerning Asphyxiating Gases and the 1907 Hague Convention of Land Warfare, both the Allies and Central Powers introduced chemical weapons early on in the conflict. In short order, lethal agents like chlorine, phosgene and others were commonplace on the battlefield. By 1918, more than 1.2 million gas casualties were recorded, with 90,000 killed. Although this figure represented a small fraction of the war’s total 10 million military fatalities, the threat of chemical attack terrified soldiers in the trenches. 
“If someone yelled ‘Gas’, everyone in France would put on a mask,” wrote American combat veteran Harvey Allen in his 1934 wartime memoir Towards the Flame. “Gas shock was as frequent as shell shock.” 
In all, more than 20 different chemical agents were weaponized during the four-year conflict. And each gas had its own uniquely horrifying characteristics. Here’s a rundown of some of the most feared and hated toxins used in the Great War along with their terrible effects on the human body.
Other names: Xylyl bromide
Type: Lachrymatory agent
Detection: A pale white cloud that gives off a faint smell of fly paper. Produces a strong metallic taste.
Effects: Intense and immediate irritation to the mucous membranes, chest tightness, coughing, sneezing, runny nose, shortness of breath, and temporary incapacitation. Exposure is rarely fatal.
Treatment: No treatment. Effects usually wear off within 24 hours.
Tear gas was the first chemical weapon used in World War One, making its appearance during the opening days of the fighting. As early as August of 1914, French artillery bombarded German positions with it. Two months later, the Kaiser’s troops responded in kind with sneezing gas at Neuve Chapelle. In these early incidents, the agents typically dispersed without effect. During the January, 1915 Battle of Bolimów, the Central Powers fired 18,000 shells containing concentrated doses of xylyl bromide into the Russian lines. The extreme cold rendered it inert. The legality of tear gas was debated at the time. But since it was considered neither poison nor an asphyxiating substance, few were certain if its use even violated international law. Such discussions soon became moot however as more dangerous toxins made their combat debuts.
Other names: n/a
Type: Choking agent
Detection: A pale greenish yellow cloud with a powerful odour similar to bleach.
Effects: When inhaled or mixed with body moisture, chlorine produces hydrochloric acid. Victims experience burning pain in the eyes and throat, blurred vision, coughing, difficulty breathing and pulmonary endema (fluid in the lungs). Chlorine is fatal with prolonged exposure.
Treatment: According to the U.S. Centers for Disease Control, there is no antidote for the agent. Treatment is limited to “supportive care”.
The first large scale use of chlorine occurred on April 22, 1915. German troops released more than 150 tons from 5,000 canisters along a five mile segment of the line near Ypres. The attack created 7,000 casualties among Canadian and French colonial units in the area and created widespread panic among the Allies. “Dusk was falling when from the German trenches in front of the French line rose that strange green cloud of death,” recalled one eyewitness. “Hundreds fell and died; others lay helpless, froth upon their agonized lips and their racked bodies powerfully sick with tearing nausea. The whole air was tainted with the acrid smell of chlorine that caught at the back of men’s throats and filled their mouths with its metallic taste.”  Despite their moral indignation, the British soon began releasing chlorine gas on the Western Front too. It was the single most widely used chemical weapon of the war.
Other names: CG
Type: Choking and blistering agent
Detection: Phosgene appears as a white or pale yellow cloud and features an odour similar to damp hay or corn.
Effects: Slow acting but highly toxic, phosgene produces a burning sensation in the throat and eyes. Incapacitating coughing fits and asphyxiation are accompanied by watery eyes and temporary blindness. Symptoms appear within 24 hours of initial exposure. By 48 hours, victims produce a white, yellow or pink-tinged fluid from their lungs. Some may experience low blood pressure and heart failure. Contact with the skin leads to sores similar to frostbite or heat burns.
Treatment: No antidote, “supportive care”
Developed by the French military in 1915, phosgene was by far the deadliest of all chemical weapons used in the First World War. Of the estimated 90,000 to 100,000 poison gas fatalities recorded, a full 85 percent were killed by phosgene. Difficult to detect, victims often had no idea they were breathing the agent in until they had suffered a near-fatal dose. One veteran recalled seeing terminal phosgene casualties in a dressing station coughing up pints of fluid from their lungs before finally succumbing.
Other names: Trichloromethyl chloroformate, DP
Type: Choking and blistering agent
Detection: Colourless, odourless.
Effects: Exposure produces a burning sensation, tightness in the chest, sore throat, cough, and suffocation.
Treatment: No antidote, “supportive care”.
Diphosgene was developed in Germany after the introduction of phosgene. It first appearing on the Western Front in May of 1916. DP was particularly feared because its vapours could pass through the filters used in many of the gas masks at the time.
Other names: PS
Detection: Colourless with a faint smell of flypaper.
Effects: Chlorpicrin burns the eyes, nasal passages, mouth, esophagus, and stomach of victims. Exposure causes nausea, vomiting, temporary blindness and shortness of breath.
Treatment: No antidote.
Engineered into a weapon in 1917, chlorpicrin wasn’t as deadly as other agents found on the battlefield. However, it could seep through filters on respirators of the time. It was particularly effective when mixed with other gases. Exposure created intense sneezing, discomfort and nausea in victims. Soldiers gassed with chlorpicrin would reflexively remove their gas masks to throw up and then be poisoned by accompanying toxins.
Other names: Sulphur mustard, LOST, Yellow Cross, Mustard T, and H
Type: Blistering agent
Detection: A thick, oily, brown liquid that produces a pale yellow vapour with a weak garlic, horseradish, onion or mustard odour when released.
Effects: Sulphur mustard burns its victims both inside and out attacking and destroying any tissue it comes in contact with. The first sign of exposure can take hours to appear and usually comes in the form of a mild skin irritation. Affected areas gradually turn yellow and eventually agonizing blisters form on the skin. Eyes become red, sore and runny. Extreme pain and blindness follow. Other symptoms include nasal congestion, sinus pain, hoarseness, coughing and in some cases respiratory failure. Sustained exposure will produce nausea, diarrhea and abdominal pain. Fatalities typically occur within a few days,
Treatment: No antidote, “supportive care”.
Mustard gas made its debut on July 12, 1917 when German units near the Ypres salient lobbed 50,000 shells laden with the agent into British lines. Undetected at first, within hours aid stations in the area were overwhelmed with up to 2,000 casualties. Over the month that followed, more than a million mustard gas shells were fired at Ypres. Not as deadly as other gasses, the painful and disfiguring effects of sulphur mustard shocked the world.
Other names: G-34, L, “dew of death”
Type: Blistering and choking agent
Detection: A colourless gas with a faint smell similar to geraniums.
Effects: Lewsite was produced by mixing arsenic trichloride and acetylene. Engineered to penetrate protective clothing (even rubber), it causes almost immediate pain and irritation to the skin, followed by expanding blisters. Victims also experience a burning sensation and swelling of the eyes. When lewsite comes in contact with the respiratory tract, it causes nose bleeds, sinus pain, shortness of breath, coughing and eventually suffocation. Diarrhea, nausea, and vomiting also occur. Prolonged exposure results in “lewisite shock” which is characterized by low blood pressure and then death.
Developed in the United States in 1918 as a top secret weapon, lewsite went into production just 10 days before the Armistice and subsequently was never used in the First World War. Nevertheless, the U.S. military stockpiled 20,000 tons of lewsite immediately following the peace and tested it extensively through the 1920s.
OF COURSE the poisons listed above weren’t the only chemical weapons to come out of the First World War. Here are some others:
• Chloromethyl chloroformate, developed in 1915 by the Central Powers, irritated the lungs and caused temporary blindness.
• Stannic chloride was an Allied gas first used in 1916. While not as deadly as other poisons, it produced a thick acrid smoke that choked its victims.
• Made from essential oils produced from a species of Pacific Ocean seaweed, Bromoacetone, known as BA or B-Stoff, was an extremely potent tear gas type agent. Used by both the Allies and the Central Powers, It first appeared on battlefields in 1916.
• Adamsite or DM is a vomiting agent/sneeze gas that can incapacitate victims in five to 10 minutes. It was produced by both sides during the war.
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