The Online Encyclopedia and Dictionary






Chemical warfare

Chemical warfare is warfare (and associated military operations) using the toxic properties of chemical substances to kill, injure or incapacitate the enemy.

Chemical warfare is distinct from the use of conventional weapons or nuclear weapons because the destructive effects of chemical weapons are not primarily due to any explosive force. The offensive use of living organisms or their toxic products (such as anthrax or botulin toxin) is not considered chemical warfare: their use is instead labelled biological warfare.

Chemical weapons are classified as weapons of mass destruction by the United Nations, and their production and stockpiling was outlawed by the Chemical Weapons Convention of 1993.


Chemical warfare technology

Chemical Warfare Technology Timeline
Agents Disseminaton Protection Detection
1900s Chlorine
Wind dispersal Smell
1910s Lewisite Chemical shells Gas mask
Rosin oil clothing
1920s Projectiles w/ central bursters CC-2 clothing
1930s G-series nerve agents Aircraft bombs Blister agent detectors
Color change paper
1940s Missile warheads
Spray tanks
Protective ointment (mustard)
Collective protection
Gas mask w/ Whetlerite
1960s V-series nerve agents Aerodynamic Gas mask w/ water supply Nerve gas alarm
1980s Binary munitions Improved gas masks
(protection, fit, comfort)
Laser detection
1990s Novichok nerve agents

Although crude chemical warfare has been employed in many part of the world for thousands of years, "modern" chemical warfare began during World War I. Initially, methods of delivery were somewhat crude and inefficient, and only well-known commercial chemicals or variants were used, such as chlorine or phosgene gasses.

Germany, the first side to employ chemical warfare on the battlefield, simply opened canisters of chlorine upwind of the opposing side and let the prevailing winds do the dissemination. Soon after, the French modifed artillery munitions to contain phosgene – a much more effective method that became the principal means of delivery.

Since the development of modern chemical warfare in World War I, four major themes have represented the majority of the research and development of chemical weapons that nations have pursued over the years: new and more deadly chemical weapon agents, more efficient methods of delivering the agent to the target (dissemination), more reliable means of defense against chemical weapons, and more sensitive and accurate means of detecting chemical agents.

Chemical warfare agents

A chemical used in warfare is called a chemical warfare agent (CWA), and is usually gaseous at room temperature, or is a liquid that evaporates quickly and generates toxic fumes (such liquids are said to be volatile or have a high vapor pressure). The phrase "poison gas" is often used to describe a chemical weapon deployed in gaseous form.

The earliest target of chemical weapon agent research was not toxicity, but development of agents that can affect a target through the skin and clothing, rendering protective gas masks useless. In July 1917, the Germans first employed mustard gas, the first agent that circumvented gas masks. Mustard easily penetrates leather and fabric to inflicts painful burns on the skin.


All chemical weapon agents are classified according to their persistency, a measure of the length of time that a chemical agent remains effective after dissemination. Chemical agents are classified as persistent or nonpersistent.

Agents classified as non-persistent lose effectiveness after only a few minutes or hours. Purely gasseous agents such as chlorine are non-persistent, as are highly volatile agents such as sarin and most other nerve agents. Tactically, non-persistent agents are very useful against targets that are to be taken over and controlled very quickly. Generally speaking, non-persistent agents present only an inhalation hazard.

By contract, persistent agents tend to remain in the environment for as long as a week, complicating decontamination. Defense against persistent agents requires shielding for extended periods of time. Non-volatile liquid agents, such as blister agents and the oily VX nerve agent, do not easily evaporate into a gas, and therefore present primarily a contact hazard.

Classes of chemical warfare agents

Chemical warfare agents are organized into several categories according to the manner in which they affect the human body. The names and number of categories varies slightly from source to source, but in general types of chemical warfare agents are as follows:

Classes of Chemical Weapon Agents
Class of Agent Examples Symptoms Effects Rate of Action Persistency Notes
Nerve agent Sarin, VX Difficulty breathing, sweating, drooling, convulsions, dimming of vision. Inhibits the breakdown of the neurotransmitter acetylcholine in the victim's nerves. Vapors: seconds to minutes; Skin: 2 to 18 hours VX is persistent and a contact hazard; other agents are non-persistent and present mostly inhalation hazards. Nerve agents are hundreds to thousands times more lethal than blister, pulmonary or blood agents.
Blood agent Hydrogen cyanide Rapid breathing, convulsions, and coma. Prevents the normal use of oxygen by the body tissues so that vital organs cease to function within minutes. Immediate onset Non-persistent and an inhalation hazard. All based on cyanide
(Blister agent)
Mustard gas, Lewisite Burning or stinging of eyes and skin. Creates extreme burning pain; conjunctivitis; large water blisters on the skin that heal slowly and may become infected. Vapors: 4 to 6 hours, eyes and lungs affected more rapidly; Skin: 2 to 48 hours Persistent and a contact hazard. Used to incapacitate rather than kill, overloading the medical facilities.
Pulmonary agent
(Choking agent, lung toxicants)
Phosgene Difficulty breathing; tearing of the eyes. Damages and floods the respiratory system, resulting in suffocation; survivors often suffer chronic breathing problems. Immediate to 3 hours Non-persistent and an inhalation hazard. These were commonly used in World War I, but were rendered mostly obsolete by the more effective nerve agents.
Lachrymatory agent Tear gas, pepper spray Powerful eye irritation Causes severe stinging of the eyes and temporary blindness. Immediate Non-persistent and an inhalation hazard. In recent decades these agents are usually used for riot-control purposes, therefore they are also often called riot control agents.
Incapacitating agent BZ Confusion, confabulation, hallucination, and with regression to automatic "phantom" behaviors such as plucking and disrobing. Decreases effect of acetylcholine in subject. Causes peripheral nervous system effects that are the opposite of those seen in nerve agent poisoning. Inhaled: 30 minutes to 20 hours; Skin: Up to 36 hours after skin exposure to BZ. Duration is typically 72 to 96 hours. Extremely persistent in soil and water and on most surfaces; contact hazard. -

There are other chemicals used militarily that are not considered to be "chemical weapon agents," such as:

Chemical weapon designations

Most chemical weapons are assigned a one to three letter "NATO weapon designation" in addition to, or in place of, a common name. Binary munitions, in which precursors for chemical weapon agents are automatically mixed in shell to produce the agent just prior to its use, are indicated by a "-2" following the agents designation (for example, GB-2 and VX-2).

Some examples are given below:

Blood agents: Vesicants:
Pulmonary agents: Incapacitating agents:
Lachrymatory agents: Nerve agents:

Chemical agent delivery

The single most important factor in the effectiveness of chemical weapons is the efficiency of its delivery to a target. The technical term for this process of delivery is dissemination. The most common techniques include munitions (such as bombs, projectiles, warheads) that allow dissemination at a distance and spray tanks allowing dissemination from low-flying aircraft. Developments in the techniques of filling and storage of munitions have also been important.

Although a there have been many advances in chemical weapon delivery over the past 90 years, it is still difficult to achieve effective dispersion and dissemination, primarily because dissemination is very dependent on atmospheric conditions. For this reason, weather observation and forecasting are essential for maximizing the probability of effective weapon dissemination and reducing the risk of injuring friendly forces.


Dispersion is the simplest technique of delivering an agent to its target. It consists of placing the chemical agent upon or adjacent to a target immediately before dissemination, so that the material is most efficiently used.

World War I saw the earliest implementation of this technique, when German forces simply opened canisters of chlorine and allowed the wind to carry the gas across enemy lines. While simple and easy, this technique had numerous disadvantages. First and foremost, delivery depended greatly on wind speed and direction. If the wind was fickle, as was the case at Loos, the gas could blow back, causing friendly casualties. Gas clouds gave plenty of warning, allowing the enemy time to protect themselves, though many soldiers found the sight of a creeping gas cloud unnerving. Also gas clouds had limited penetration, only capable of affecting the front-line trenches before dissipating. Although it produced limited results in World War I, this technique shows how simple chemical weapon dissemination can be.

Shortly after the German employment of "open canister" dissemination, French forces developed a technique for delivery of phosgene in a non-explosive artillery shell. This new technique overcame many of the risks of dealing with gas in cylinders. First, gas shells were independent of the wind and increased the effective range of gas, making anywhere within reach of the guns vulnerable. Second, gas shells could be delivered without warning, especially the clear, nearly odorless phosgene — there are numerous accounts of gas shells, landing with a "plop" rather than exploding, being initially dismissed as dud high explosive or shrapnel shells, giving the gas time to work before the soldiers were alerted and took precautions.

The major drawback of artillery delivery was the difficulty of achieving a killing concentration. Each shell had a small gas payload and an area would have to be subjected to a saturation bombardment to produce a cloud to match cylinder delivery.

Over the years, there were some refinements in this technique. For example, chemical artillery rockets of the 1950s and early 1960s contained a multitude of submunitions, so that a large number of small clouds of the chemical agent would form directly on the target.

Thermal dissemination

Thermal dissemination is the use of explosives or pyrotechnics to deliver chemical agents to a target. This technique, developed in the 1920s, was a major improvement over earlier dispersal techniques, in that it allowed significant quantities of an agents to be disseminated over a considerable distance. Thermal dissemination remains the principal method of disseminating chemical agents today.

Most thermal dissemination devices consist of a bomb or projectile shell that contain a chemical agent and a central "burster" charge; when the burster detonates, the agent is expelled laterally (to the sides).

Thermal dissemination devices, though common, are not particularly efficient. First, a percentage of the agent is lost by incineration in the initial blast and by being forced onto the ground. Second, the sizes of the particles vary greatly because explosive dissemination produces a mixture of liquid droplets of a variable and difficult to control size.

The efficacy of thermal detonation is greatly limited by the flammability of some agents. For flammable aerosols, the cloud is sometimes totally or partially ignited by the disseminating explosion in a phenomenon called flashing. For example, explosively disseminated VX will ignite roughly one third of the time. Despite a great deal of study, flashing is still not fully understood, and a solution would represent a major technological advance.

Despite the limitations of central bursters, most nations will use this method in the early stages of chemical weapon development in part because their standard munitions can be adapted to carry the agents.

Aerodynamic dissemination

Aerodynamic dissemination is the non-explosive delivery of a chemical weapon agent from an aircraft, allowing aerodynamic stress to disseminate the agent. This technique is the most recent major development in chemical agent dissemination, originating in the mid-1960s.

This technique eliminates many of the limitations of thermal dissemination by eliminating the flashing effect and theoretically allowing a very precise control of particle size. In actuality, however, the altitude of dissemination, wind direction and velocity, and the direction and velocity of the aircraft influence the particle size a great deal. There are other drawbacks also: ideal deployment requires a precise knowledge of aerodynamics and fluid dynamics, and because the agent must usually be dispersed within the boundary layer (less than 200–300 ft above the ground), it also puts pilots at risk.

Significant research is still being applied toward this technique. For example, by modifying the properties of the liquid, its breakup when subjected to aerodynamic stress can be controlled and an idealized particle distribution achieved, even at supersonic speed. Additionally, advances in fluid dynamics, computer modeling, and weather forecasting allow an ideal direction, speed and altitude to be calculated, such that weapon agent of a predetermined particle size can predictably and reliably hit a target.

Protection from chemical agents