Chlorine
Of the 70,552 American soldiers poisoned with gasses during World War I, 1,842 were exposed to chlorine gas. First used as a chemical weapon at Ypres, France in 1915, chlorine gas acts a pulmonary irritant that causes acute damage in the upper and lower respiratory tract. By the end of World War I, Germany, France and the United Kingdom had all used chlorine gas. Not very efficient and in low concentrations, it was observed that even rudimentary protection would prevent a soldier from succumbing to its full effects. Its use, however, was still enough to cause "gas hysteria" during an attack. Chlorine is a greenish-yellow, noncombustible gas at room temperature and atmospheric pressure. The intermediate water solubility may not cause upper airway symptoms for several minutes. In addition, the density of the gas is greater than that of air, causing it to remain near ground level and increasing exposure time. Chlorine can be detected by odor at 0.3 to 0.5 parts per million, but distinguishing toxic air levels would be difficult until irritative symptoms are present.

Frequent exposure to chlorine gas can degrade an individual's sense of smell; workers with occupational exposure to the gas are at greater risk of inhalational damage in later years. Low concentrations of chlorine gas irritate the nasal passages and constrict the chest. In larger amounts, chlorine gas causes death by asphyxiation. Approximately 19,000mg·min/m3 is lethal dose to 50 percent of exposed adults. Though not currently considered a battlefield weapon, there have been reports of its use in recent times. In the late 1990s, media sources quoted Bosnian soldiers as bragging they possessed gas grenades and other mortar weapons against Serbian forces. Croatia's UN mission issued a press statement confirming that the Bosnian Muslim forces were using gasses and that the agent was most likely chlorine gas. Chlorine is not listed as a Scheduled Chemical in the CWC.    

Chloropicrin (PS)
John Stenhouse, a Scottish chemist and inventor synthesized chloropicrin in 1848. Chloropicrin is currently used as a soil fumigant used for its broad biocidal and fungicidal properties. As a CW agent, chlorpicrin was first used by Russia during World War I, and was eventually delivered in artillery shell sand cylinders by all sides. Known to the British as "vomiting gas," the French as "Aquinite," and "Klop" by the Germans, chloropicrin has an intense odor, which is a distinctive warning property. During World War I, its use was often coupled with other agents because the agent often broke through gas mask filters, making soldiers vulnerable to other gasses. Chloropicrin is a colorless-to-light green oily liquid that is an irritant to all body surfaces. At 1 part per million (ppm), the victim experiences irritation with pain in the eyes; at 4 ppm exposed individuals are incapacitated; and at 20 ppm the victim has definite bronchial or pulmonary lesions. Overexposure leads to irritation of the nose and throat leading to coughing, labored breathing, sore throat, dizziness, bluish skin, vomiting and in some instances chemical pneumonitis and pulmonary edema. Skin contact can lead to chemical burns-exposure through damaged skin causes similar symptoms as those resulting from inhalation and prolonged eye exposure can result in blindness. Because of its strong odor, wide use in commercial applications and being one-fourth less toxic than phosgene, chloropicrin has not received the same attention as more potent CW agents. Although not flammable, chloropicrin presents a significant explosion hazard if involved in a fire and bulk containers are shock sensitive and can detonate. Chloropicrin decomposes in the environment.    

Diphosgene (DP)
Liquid at room temperature, diphosgene is easier to handle than phosgene and is more persistent than chlorine or phosgene. The German army first used diphosgene during World War I in May 1916. Diphosgene is a colorless liquid that emits an odor similar to green corn or new mown hay. A lethal dose is 3,000mg·min/m3 for 50 percent of resting adults exposed to the gas. Symptoms can be delayed three hours or more, though immediate symptoms may appear after exposure to high concentrations of diphosgene. Essentially, the body turns diphosgene into phosgene, producing the same results as if the victim were exposed to phosgene gas. Because diphosgene has a strong tearing effect, it has less surprise value than phosgene when used on troops. In addition, it's lower volatility makes it more difficult to set up an effective surprise concentration.    

Perfluoroisobutylene (PFIB)
Perfluoroisobutylene is an industrial gas that is a byproduct of the overheating and during the production of Teflon®. PFIB has the potential to be an asphyxiating weapon, causing pulmonary edema even in low concentrations. The effects of exposure of PFIB, called "polymer fume fever," begin to appear one to two hours after exposure and is often mistaken for influenza. Like phosgene, however, severe symptoms appear suddenly over 24 to 48 hours after exposure. Exposure to PFIB can result in pulmonary edema. Because of its high toxicity the United Kingdom brought PFIB to the attention of the Conference on Disarmament in 1989 and it was entered as a restricted chemical under the CWC.   

Phosgene (CG)
Phosgene-also called collognite or D—Stoff—was first used in the dye industry before it was used as a battlefield weapon. The first recorded use of phosgene was in the early hours of 19 December 1915, when the Germans released phosgene gas against British positions in Ypres, France. The attack resulted in 1,069 casualties, of which 116 were fatal. Within a year of the first attack with phosgene, the British were manufacturing supplies of phosgene gas at Porton Down. It was filled into artillery shells for British gunners for use in the Second Battle of the Somme in June 1916. By some estimates, over 80 percent of chemical agent fatalities in World War I were caused by phosgene. Phosgene gas will incapacitate a man within a few seconds if exposed to 100 parts per 10 million. Fatalities occur if he is exposed to concentrations of 200 parts per 10 million for one or two minutes. Phosgene kills any breathing thing by attacking the lung capillaries and then the membranes of the lung sacs, causing them to flood with watery fluids. Following exposure, death may follow within hours or up to a day. Phosgene is particularly dangerous because it does not detoxify naturally, has a cumulative effect on its victims and may persist in sheltered areas and buildings. Britain unilaterally destroyed its phosgene stocks after World War II. Phosgene was also produced and stockpiled by the Soviet Union and the United States. Egypt used Soviet-supplied phosgene stocks in the Yemeni civil war between 1963 and 1969.