Nerve gases were first developed (but not used) by Germany during World War II. These agents are hundreds of times more poisonous than the poison gases of World War I; they kill when they are inhaled or when they are deposited as liquid droplets on the skin. The term "nerve gas" derives from the fact that these agents operated by interfering with the transmission of nerve impulses across synapses. They do so by inactivating the enzyme cholinesterase, which normally functions to terminate the transmission of a nerve impulse. In the presence of a nerve agent, nerve impulses continue without control, causing a breakdown of respiration and other functions. Death caused by nerve-gas poisoning results from asphyxiation. It is preceded by blurring of vision, intense salivation and convulsions.
The nerve agents used as chemical weapons - sarin (GB), soman, tabun (GA) and VX - are members of a large family of chemicals called "organophosphate cholinesterase inhibitors". When a person is poisoned with organophosphates, the pupils constrict, muscles twitch, the person salivates, sweats and sometimes wheezes. Often there is nausea, vomiting and involuntary defecation. At higher doses, or with longer exposure, people have convulsions, lapse into unconsciousness, develop profoundly low blood pressure and stop breathing. Organophosphates are the most commonly used pesticides in the world, with hundreds of tons used every year by everyone from household exterminators to crop dusters. Unlike pesticides, however, the compounds designed as chemical weapons kill people and animals at extremely low doses.
The stockpile of nerve gases in the USA (at 1970) included two kinds. One is GB, a code name for isopropylmethylphosphonofluoridate. It is also known as sarin and was produced in limited amounts by Germany during World War II. Weapons containing sarin release it as a spray, which then evaporates into a colourless and odourless gas. Within the central target area of the weapon, a lethal dose can be taken in as short as 10 minutes. Since the hazard posed by sarin in mainly respiratory, a gas mask provides good protection. The second kind of nerve agent in the US stockpile is VX. The chemical formula of VX is a secret, although the WHO suggests that the agent is ethyl S-dimethylaminoethylmethylphosphonothiolate. It, like sarin, was the outcome of insecticide research. Also a liquid, but seven times more toxic than sarin and much less volatile, VX is lethal either when inhaled or deposited on the skin. VX kills in a matter of minutes, and by contaminating the ground and objects on which it is deposited it can make an entire area hazardous for many days. (Leaking VX was responsible for killing sheep in Utah.) Since contact with even a small droplet of VX can be fatal, adequate protection requires the wearing of a special suit as well as a gas mask.