Chemical agents of warfare include all gaseous, liquid or solid chemical substances which might be employed because of their direct toxic effects on man and animals. (This excludes substances whose effect is primarily physical, such as incendiary weapons, high explosives and smoke). Chemical weapons also include the chemical's precursors, the munitions and devices designed to deliver them, and any equipment specifically designed for their use in warfare.
Nerve agents (chemicals of the same family as organophosphorus insecticides) are the most lethal of the classical chemical warfare agents, killing by poisoning the nervous system and disrupting bodily functions. Blister agents (such as mustard gas) burn and blister the skin (causing more casualties than any other agent in the first world war). Vesicants are blistering and tissue-injuring agents which produce injuries similar to burns, although the mechanism behind the injury is different. Choking agents (such as phosgene) are highly volatile liquids. Toxins (such as mycotoxins and botulin toxin) are biological substances chemical substances produced biologically (although many of them have also been synthesized) which are very highly toxic. Tear gas and harassing agents are sensory irritants causing pain in the eyes, tear flow, and severe irritation of the upper respiratory tract (and have been widely used as riot control weapons); they can also cause skin irritation, nausea and vomiting. Psycho-chemicals are drug-like chemicals intended to cause temporary mental derangement, including psychosis. Cyanides (blood agents) cause headaches, weakness, disorientation and nausea in low doses; higher doses are acutely lethal causing circulatory effects, seizures and respiratory and cardiac failure. Incapacitating agents produce physiologic or mental effects, or both. They render individuals incapable of performing normal activities. DZ (3-quinuclidinyl benzilate) is the most commonly used. It is pharmacologically related to anticholinergic drugs and is present within some over-the-counter sleeping medications. Tear gases are used primarily for riot control and cause irritation to the eyes, respiratory tract, and skin. Herbicides may also be used to poison or defoliate plants.
Burning sulphur is said to have been used by the Spartans at Thermopylae, but the first use of chemical operations in modern times occurred during World War I. For example sulphur mustard (HD) gas was used against the Allies in 1917. In all, some 100 million kilograms of chemical, lethal and non-lethal gases were used by the seven parties. There were 100,000 fatalities and over one million other poison-gas casualties. Between World War I and World War II, mustard gas was used with considerable effect against Abyssinian tribesmen and troops. Other major instances of use were in the Italian invasion of Ethiopia (1935-36), and the Japanese invasion of China (1937-45). Chemical operations were not used in World War II, probably because of the high state of preparedness on both sides and because the Germans were not aware that the Allies had no nerve agent capability. Chemicals were , however, used by the Nazis during the Second World War to gas concentration camp civilians; and, although chemical weapons were not employed in combat, almost all the belligerents maintained stocks, most of which were destroyed after the war (to a large extent by dumping into the sea; where this was done in shallow waters, such as in the Baltic, it created severe problems for fishermen which still persist).
Defoliant chemicals were originally developed by the UK and used in the Malayan anti-terrorist campaign in 1948-60. During the Second Indochinese War, the USA used Agent Orange, a defoliating herbicide, and the riot-control agent CS. The USA used the same quantity of chemicals as was used by all the belligerents in the First World War, about 100 million kilograms (1965-1970).
The US Army divides chemical warfare agents according to different features including the nature of their use, their persistence in the field, and physiologic effects. They may produce incapacitation, serious injury and death. For tactical purposes, chemical warfare agents may be divided into two main categories:
(1) Persistent agents are those that remain dangerous for a considerable amount of time unless action is taken to destroy or neutralize them. They are usually liquid or solid at normal temperatures.
(2) Nonpersistent agents are those that remain in effective concentrations for only a short time. They are released as airborne particles of a solid, droplets of a liquid, or as true gases. They are affected by prevailing weather conditions and are quickly dispersed, so that the locality in which they have been released soon ceases to be contaminated.
For medical and service classification, chemical warfare agents are usually classified according to pharmacologic principles and their overall effects on combat efficiency.
Chemical weapons technology has progressed rapidly in recent years. The cheapness of materials now means that many more countries have the capacity to produce them. The intent to use chemicals in warfare is indicated by stockpiles of weapons and other military preparedness. For example, the Russian SCUD B missile can be equipped with a chemical warhead. Soviet stockpiles of chemical weapons are extensive and include the extremely toxic nerve agents sarin and soman, together with VX and the blistering agents mustard gas and lewisite. The USA halted large scale production of poison gas munitions in 1969, but have a 30,000 tonne stockpile; a multi-billion dollar budget to produce binary nerve gas weapons has been discontinued. France and the UK have been reported to be manufacturing and stocking chemical weapons, although both deny possession (the UK destroyed its then existing stock during the 1950's). Western intelligence sources claim that over twenty nations, in addition to the USA, Russia and Iraq, either possess chemical weapons or have an active programme for the development of such weapons. These nations include many in the Middle East (Libya, Egypt, Syria and Iran) as well as China, Vietnam and North Korea. Allegations that the former Soviet Union used chemical weapons in Afghanistan and Southeast Asia (1979-82) were never proven. The "yellow rain" turned out to consist, at least in part, of bee faeces, although uncertainties exist over any toxic substances. Iraq used mustard agent and nerve agents against Iran in the period 1983-88, including the nerve gas sarin, against northern Kurds in 1988. After the Gulf War in 1991, the Iraqi chemical weapons were destroyed by the United Nations.
Hundreds of Gulf War veterans have complained of severe flu-like symptoms (as many as 2,000 may be affected), but it is not know if chemical weapons were the cause. In 1993 it was alleged that Iraq had rebuilt its chemical weapons factories and had used such weapons (possibly white phosphorous) against Arabs located in the Hammar Marshes south of the Euphrates river. The Pentagon had insisted that it learned only in 1996 of an incident in which large numbers of American troops may have been exposed to chemical weapons - an event in March 1991, in which American combat engineers blew up an Iraqi ammunition bunker that was later determined to have contained tons of nerve gas and mustard agent.
Incapacitating agents produce physiologic or mental effects, or both. They render individuals incapable of performing normal activities. DZ (3-quinuclidinyl benzilate) is the most commonly used. It is pharmacologically related to anticholinergic drugs, and is present within some over-the-counter sleeping medications.
Tear gases are used primarily for riot control and cause irritation to the eyes, respiratory tract, and skin. Long-term effects of repeat exposure to these gases are not well studied.