In March 1984, an Iranian soldier attacking Iraq during the conflict between those two States came under fire from artillery shells that emitted a heavy smoke smelling of garlic. Within a few minutes, the soldier’s eyes burned and his skin began to itch, redden, and blister. Five days later the skin on his neck, chest, and shoulders began to peel off. Shortly afterward, the soldier died.

A UN investigation of several such instances concluded that chemical weapons, including mustard gas and the nerve agent known as Tabun, had been used. By the end of the war, Iran claimed tens of thousands of chemical weapons’ casualties. There was no doubt that Iraq had broken the 1925 Geneva Protocol for the Prohibition of the Use of Asphyxiating, Poisonous, or other Gases, and of Bacteriological Methods of Warfare, nor that Iran had retaliated in kind, albeit briefly and less effectively.

Since then, Saddam Hussein has apparently stockpiled chemical and biological weapons, and there have been uncorroborated allegations of the use of such weapons by other States: the use of gas by South African-backed forces in Mozambique, by contestants in the conflict between Azerbaijan and Armenia, by Turks against Kurds, and in the Sudan civil war. More recently, there have been unverified claims by a Soviet-era defector that the Russians may have developed super-strains of germ weapons, and some of these may still exist in the Russian arsenal.

For the observer at the front line, accusations of the use of chemical and biological weapons are almost impossible to verify on the spot. Only after a prolonged investigation that involves examining the corpses of the victims, interviewing survivors, and searching for residues of the weapons ingredients and products of chemical reactions involving such ingredients, can the truth be known—and sometimes not even then.

One of the lingering military mysteries of the Cold War was Moscow’s alleged use of so-called yellow rain against Hmong tribesmen in Laos. Yellow rain was said by the United States to be a deadly chemical and biological weapon that was sprayed from light aircraft and fell “like a yellow rain,” but an independent inquiry by American and British scientists suggested a perfectly natural explanation: the defecation of honey bees. When bees defecate they leave the hive in a swarm, and the result, for anyone standing underneath the flight path, can be something like a yellow rain. The waste matter contains toxins that can make people ill. However, the U.S. government has not officially accepted the bee theory, nor dropped its charges of yellow rain.

Put together over the years, these reports of the use of banned weapons underscored the urgency of tightening international controls. The 1925 Geneva Protocol, eventually ratified by 149 states, prohibited only the “first use” of chemical and biological weapons. Countries were allowed to develop and stockpile chemical weapons for “defensive” purposes: the law did not prohibit reprisals with chemical weapons. The ban did not apply against a country’s own nationals, nor tear gases, including CS gas. The 1972 Biological Weapons Convention renounced germ weapons totally, including their development and stockpiling. In 1993, the new Chemical Weapons Convention was opened for signature in Paris. It entered into force on April 29, 1997, and 111 states have ratified it, including the U.S. and Russia.

The essence of the fifty-thousand-word treaty is that each State party undertakes never, in any circumstances, to develop, produce, otherwise acquire, stockpile, or retain chemical weapons, or transfer them directly or indirectly to anyone; never to use chemical weapons or engage in any preparations for doing so; and never to assist, encourage, or induce, in any way, anyone to engage in any activity prohibited by the treaty.

By “chemical weapons” the treaty means munitions or other devices using toxic chemicals to cause death, temporary incapacitation, or permanent harm to humans or animals. The treaty does not prohibit the development of toxic chemicals for industrial, agricultural, research, medical, pharmaceutical, or other peaceful purposes, or purposes related to protection against chemical weapons, and law enforcement including domestic riot control. Riot control agents, such as CS gas, cannot be used as a method of warfare, a distinction not always easy to make. (In a move to which no other party to the convention took exception, President Bill Clinton pledged to Congress that the United States will not be restricted in the use of riot control agents in two circumstances: conflicts to which the United States is not a party but is playing a peacekeeping role, or locations where U.S. troops are stationed with the approval of the host State.)

Each State undertakes to destroy, within ten years, its chemical stockpiles and production facilities that can produce more than one ton of chemical weapons per year.

The treaty set up a new international body, the Organization for the Prohibition of Chemical Weapons, headquartered in The Hague. It will oversee treaty compliance and investigate any claims of violation by treaty-member States. The Secretary-General of the United Nations is empowered by UN resolution to investigate any claims of violations by nonmember States.