a. Nerve agents are primarily organophosphorus esters similar to insecticides. Those of military importance are combined under this term. Although some have been given names, they are usually known by their code letters: GA; GB; GD; and VX. They are all liquids, varying in volatility that is in a range between gasoline and heavy lubricating oil. Their freezing points are -40 degrees Celsius or lower.

(1) Liquid nerve agents are pale yellow to colorless and are almost odorless. They are moderately soluble in water and highly soluble in lipids (oil). They are rapidly destroyed by strong alkalies and chlorinating compounds. Normal clothing is readily penetrated by liquid or vapor agents. Butyl rubber and synthetic material are more resistant than natural fibers. Agents can penetrate into nonabsorbent material such as web belts and can continue to present a hazard by desorption (off-gassing) of the vapor. Although local sweating and twitching may occur, usually there is no local irritant change after cutaneous exposure. Toxicity depends upon the route of entry and physical characteristics.

(2) Nerve agents strongly inhibit the cholinesterase enzymes. When acetylcholine is released by the nerve junction, it is hydrolyzed by the enzyme. Acetylcholine is the chemical mediator for transmission of the nerve impulses in numerous synapses of the central nervous system (CNS) and the autonomic nervous system and at the endings of the cholinergic nerves (for example: affecting the smooth muscles of the iris, ciliary, bronchial tree, and gastrointestinal tract). The inhibition of cholinesterase by nerve agents is almost irreversible, so the effects are prolonged. Until the cholinesterase level is restored to normal, there is an increased susceptibility to nerve agent exposure. During this time, the effects of repeated exposure are cumulative and the patient may feel "subpar" (for example: tired, fatigue easily, poor appetite, impaired concentration) until recovery is complete.

(3) Nerve agent poisoning is easily identified by the characteristic signs and symptoms as follows:

(a) MILD symptoms (self-aid). Casualties with MILD symptoms may experience most or all of the following:

(b) Casualties with MODERATE symptoms (buddy aid) will experience an increase in the severity of most or all of the MILD symptoms. Especially prominent will be an increase in fatigue, weakness, and muscle fasciculations. The progress of symptoms from MILD to MODERATE indicates either inadequate atropine treatment or continuing exposure to agent.

(c) SEVERE symptoms (buddy aid). Casualties with SEVERE symptoms may experience most or all of the MILD symptoms, plus most or all of the following:

b. There are three major families of blister agents (vesicants); HD and HN, L, and CX. Most vesicants (except CX) are relatively persistent. Mustards can modify the structure of nucleic acids, cellular membranes, and proteins by combining with certain functional groups (particularly the sulfhydryl-containing enzymes) for which they have an affinity.