Chemical agents may also be classified as lethal or nonlethal. Lethal agents are those that result in a 10 percent or greater death rate among casualties. They may further be classified as persistent or nonpersistent, depending on the length of time they retain their effectiveness after dissemination.
NERVE AGENTS
Physically, nerve agents are odorless, almost colorless liquids varying greatly in viscosity and volatility. They are moderately soluble in water and fairly stable unless strong alkali or chlorinating compounds are added. They are very effective solvents readily penetrating cloth either as a liquid or vapor. Other materials, including leather and wood, are fairly well penetrated. Butyl rubber and synthetics, such as polyesters, are much more resistant.
Pharmacologically, the nerve agents are cholinesterase inhibitors. Their reaction with cholinesterases is irreversible; consequently, the effects of inhibition are prolonged until the body synthesizes new cholinesterases.
Signs and Symptoms of Exposure
Nerve agent intoxication can be readily identified by its characteristic signs and symptoms. If a vapor exposure has occurred, the pupils will constrict, usually to a pinpoint; if the exposure has been through the skin, characteristic local muscular twitching will occur.
Other symptoms will include rhinorrhea, dyspnea, diarrhea and vomiting, convulsions, hypersalivation, drowsiness, coma, and unconsciousness.
Treatment
Specific therapy for nerve agent casualties is atropine, an acetylcholine blocker. For immediate self-aid or first aid, each individual is issued three automatic injectors containing 2 mg of atropine sulfate for intramuscular injection or two autoinjectors containing the Nerve Agent Antidote. These injectors are designed to be used by individuals on themselves when symptoms appear. After the first injection, if the symptoms have not disappeared within 10 to 15 minutes, another injection should be given. If the symptoms still persist after an additional 15 minutes, a third injection may be given by nonmedical personnel.
For medical personnel, the required therapy is to continue to administer atropine at 15-minute intervals until a mild atropinization occurs. This can be noted by tachycardia and a dry mouth. Atropine alone will not relieve any respiratory muscle failure. Prolonged artificial respiration may be necessary to sustain life.
Oxime therapy, using pralidoxime chloride, or 2-PAM Cl, may also be used for regeneration of the blocked cholinesterase. For individuals treated initially with the new autoinjector, additional oxime therapy is generally not medically indicated; it is already included in the autoinjector.
VESICANTS
Blister agents or vesicants exert their primary action on the skin, producing large and painful blisters that are incapacitating. Although vesicants are classed as nonlethal, high doses can cause death.
Common blister agents include mustard (HD), nitrogen mustard (HN), and Lewisite (L). Although each is chemically different and will cause significant specific symptoms, they are all sufficiently similar in their physical characteristics and toxicology to be considered as a group. Mustards are particularly insidious because they do not manifest their symptoms for several hours after exposure. They attack the eyes and respiratory tract as well as the skin. Further, there is no effective therapy for mustard once its effects become visible. Treatment is largely supportive, to relieve itching and pain and to prevent infection.
Mustard (HD) and Nitrogen Mustard (HN)
HD and HN are oily, colorless or pale yellow liquids, sparingly soluble in water. HN is less volatile and more persistent than HD and has the same blistering qualities.
SYMPTOMS.— The part of the body most vulnerable to mustard gas is the eyes. Contamination insufficient to cause injury elsewhere may produce eye inflammation. Vapor or liquid may burn any area of the skin, but the burns will be most severe in the warm, sweaty areas of the body; that is, the armpits, groin, and on the face and neck. Blistering begins in about 12 hours but may be delayed for up to 48 hours. Inhalation of the gas
